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Since at least 1865, when Congress voted to set up the 's Bureau, Americans have debated how and whether to compensate former slaves. In 2020, when Donald Trump had reawoken the left and , an unarmed African-American man, was murdered by a policeman, the idea of —paying money to the descendants of slaves—became almost mainstream. Some Democratic , under pressure from activists and eager to be on the right side of history, agreed to set up commissions to study the idea. A few years later, those commissions are coming back with recommendations. Cash reparations for are . Only 30% of Americans support the policy. Most of those alive today played no role in Jim Crow; none can reasonably be blamed for slavery. Nor are black Americans the only disadvantaged group: try telling an unemployed Appalachian coalminer why finite tax dollars should go on reparations rather than, say, better schools or public health. Still, unpopular policies are sometimes right. Are cash reparations for African-Americans one such case? Not long after slavery ended, the Freedmen's Bureau collapsed. Few freedmen received compensation and many ended up working as sharecroppers for their former masters in something close to indentured servitude. Emancipation was followed by the creation of a two-tier version of citizenship that lasted for a century. Until the 1960s, many black Americans lived in fear of terrorism, were shut out of many neighbourhoods and could not vote. Many were also excluded from supposedly universal programmes like the GI Bill. Plenty of the people who suffered directly from this system are still alive today. And in many cases their children and grandchildren have inherited disadvantages that have their in state-sanctioned discrimination. How much present racial inequality is due to that inheritance is impossible to quantify. But it is not zero and it is not 100%. The moral sentiment about reparations rests on these centuries of unfairness. Yet the cruelty of history is not the main argument. If the past were the same but there were no present-day racial gaps in income or life expectancy, the case for reparations would be weak. The main policy question, then, is how to help those who have been left behind. California shows how, in practice, it is impossible to create an actuarial table of injustice that can be consulted to determine how much cash is owed and to whom. California outlawed slavery when it joined the union in 1850, so its commission concentrated on making amends for current racial disparities. These are considerable, as they are nationwide. African-Americans die four years earlier than white Americans on average. (Perhaps less noticed is that black Americans have enjoyed the fastest gains in life expectancy over the past 20 years.) For the purpose of its calculations, the commission assumed that a life is worth $10m and, speciously, that all racial disparities in outcomes are due to , current or historical. It then calculated how much African-American Californians are owed. The maximum payout per person came to $1.2m. San Francisco, naturally, created its own commission, which put the figure higher, at $5m. The bill for the statewide scheme could exceed $800bn, though the commission deems even that sum to be merely a down payment. This comes as California faces a $32bn budget shortfall on an overall annual budget of $300bn. Then there is the difficulty of determining who is eligible for reparations. America, happily, is more racially fluid than when the Jim Crow era ended, which makes that hard. The commission's answer is to set up another body to determine individual claims, which is just to pose the question again. If the aim of the policy is to ease disadvantage, that can be done with race-neutral anti-poverty programmes. The expanded child-tax credit, which was part of Congress's response to covid-19, cut child poverty nationwide. It did the most for African-American children, narrowing disparities, and was popular. This is a route to the same end that is achievable. For Democrats, whose task is to build as big a coalition as possible to defeat Mr Trump's movement, it is hard to think of a policy better designed to set different groups of supporters against each other than cash reparations. Or one easier to lampoon in attack ads: "Californian liberals vote to give Hollywood star $1m!" Gavin Newsom, the governor, appears to be looking for ways to quietly ignore the state commission. London Breed, San Francisco's mayor, has not endorsed the city council's proposal. Both should say clearly that they oppose cash reparations, and then propose policies to narrow disparities which most Americans would happily support.

IV. REPARATIONS WILL NOT ALLEVIATE THE PROBLEMS FACING BLACKS TODAY: Reparations advocates fail to realize that reparation handouts will never cure the ills Blacks face today as individuals and as a community.' 0' Reparations will not give Blacks self-worth. It will not lower poverty, the crime rates or out of wedlock birth rates, even though proponents try to use these statistics to justify their claim that the government should pay reparations. These problems are engrained within our culture. They are a mindset that cannot be changed by any proposed reparations. Instead, proponents should devote their time and energy to alleviate theses problems by proposing viable solutions that will truly impact Blacks in a positive way. Reparations supporters should preach self-reliance to the black community rather than advocating for an unreasonable and unrealistic fix to current social ills. When people are not forced to take responsibility for their lives, this attitude actually reinforces the perpetual cycle of problems facing the black community.' 0 2 Blacks should stop treating themselves as victims and take responsibility for their lives.'0 3 But reason has been the first casualty in the Victimhood Sweepstakes, from which the reparations movement gets it casus belli. Will the reparations issue rear its head again if paid to black Americans? It certainly will. Many other ethnic groups will ask for handouts until our country is bankrupt, which ultimately harms everyone. Therefore, Blacks in this country would better reach their goals by relying on themselves to attain the American Dream. As such, the focus should be on strengthening the economic base of the black community. One theory on how to do this is through cooperative economics, which promotes the reinvigoration of a community by encouraging community residents to financially patron local businesses. In turn, these businesses will reinvest their resources into community development enterprises.' 0 4 Black Cooperative Economics is an attempt to reinvigorate the black community by establishing a system of economic self sufficiency within the community. 0 5 Black residents support black businesses while these same businesses provide the capital base for the community, thus a creating a beneficial cyclical effect. 10 6 The premise behind black cooperative economics is that Blacks should not depend upon anyone, especially the government, to invest money into black communities in order to strengthen the black community. The result of this cyclical economic structure and the element of exclusivity yield a self-sufficient economic system that is durable and permanent. In addition to encouraging responsibility of black businesses to reinvest within the black community, black middle-class professionals are encouraged to prime the capital pump by investing within black communities. 1° 8 Consequently, a self-sufficient enterprise is born and sustained by the black community for its own benefit. These ideas would be a healthier and more productive way to address the problems of black today instead of wasting time and energy on the reparationists' lost cause.

The contemporary paradigm for African-American reparations fundamentally fails to address what should be its most vital component. Of the three essential elements of a successful reparations campaign-apology, award, and nonrepetition through reconciliation-the most vital is nonrepetition. In past "successful" reparations campaigns, the offending parties have issued apologies and awards, but have neither challenged nor dismantled the attitudes or infrastructures from which wrongful acts emerged, leaving open the likelihood of wrongful acts occurring again. Any campaign that neglects the nonrepetition element runs the risk of strengthening the status quo. In this Article, Professor Burkett argues that in order for a reparations campaign to be a true success for African-Americans, it must include a nonrepetition element. To do so, the reparations movement must embrace a reconciliation model that is forward looking, and concerned with the methods of deterring future bad acts for ultimate, complete, and successful repair. In the current discourse on African-American reparations, Professor Burkett argues, nonrepetition through reconciliation is woefully underemphasized. The incorporation of the nonrepetition element is particularly important in the American context. From the nation's earliest days, the American political and economic landscape has evolved in a particularly pernicious manner, creating and entrenching a racial and economic hierarchy that persistently subjugates African-Americans and other of-color and lowincome communities. Professor Burkett argues that in this context, a multiracial, multiethnic, and cross-class reconciliation model is vital to the success of the African-American campaign. This broad-based approach, the author maintains, is the only way to ensure nonrepetition. The contemporary paradigm for African-American reparations for slavery and its legacy fundamentally fails to address what should be its most vital component. Any successful reparations must contain three critical elements. The first element on the path to repair is an apology. The second element is a monetary or other award that gives actual or symbolic weight to that apology. However, the true weight of an apology and redress is felt in the commitment by the perpetrator not to repeat the act. It follows the simple lesson taught to children- "sorry" is limited in its effect. One must promise to try, vigilantly, not to commit the act again. An apology and remuneration alone are, therefore, insufficient. The third and most vital element of a reparations campaign is the guarantee of nonrepetition. The current movement for reparations, however, fails to demand and secure this most important element of repair. The movement for African-American reparations thus seeks remedies that fall short of forcing structural change that will produce true social transformation. It makes an impossible request in a hostile arena, and at the same time does little to dissipate the very cloud of hostility that makes the social, legal, and political space so inhospitable. In short, the current movement for African-American reparations simply asks for too little. In the current discourse on African-American reparations for slavery and its legacy, the focus on monetary reparations for injuries suffered by African-Americans is misguided.' The emphasis on reparations with respect to actual monetary losses, as well as psychological and community damages, pulls energy away from efforts to address larger systemic changes that need to occur in a race-riddled society. Furthermore, in accepting traditional forms of reparations, African-Americans aid in perpetuating the very system that allows for their persistent subjugation and the subjugation of other of-color communities. Although a number of proposed remedies focus on building programs, arguments demanding monetary liability are often said and heard most loudly, and, to be sure, money transfers are integral to erecting necessary programs. This focus on money transfers or payments is based largely on the belief that American society is so riddled with racism and its permanency that monetary awards are the only true means of change for which African-Americans can hope. Closing the economic gap between black and white Americans is a vital component in remedying the plight of African-Americans. It is impossible, however, for money allotments to have substantive and lasting meaning beyond temporary currency in the marketplace. Rather than risking reinforcement of the status quo with respect to widening class divides and the formidable power of monied groups, challenging the economic structure and the manner in which economic and political power exists in America is the conceptual core around which reparationists must frame their argument and the ensuing debate. Thus, I contend that the reparations movement should focus on the larger goal of transformation by meeting the demands of the nonrepetition prong. I fully acknowledge that this is a far-reaching task, but it is necessary to repair the damage done. Realization of any number of alternative futures that may pull American society out of its current loop requires an adequate response to centuries of legalized subjugation followed by extralegal oppression, individual and systemic. This may well demand a fundamental shift in America's economic, political, and social structures. While crafting and implementing differing structures may be a daunting task, African-Americans must begin the long march toward realizing these alternative futures. The reparations debate itself provides an incomparably valuable opportunity for all Americans to come to terms with the truth of their history. It is an historic moment that offers a chance to rediscover, or perhaps introduce, compassion in and for all Americans. This debate provides unparalleled potential to explore the racial and economic hierarchies that have defined American social construction for over three centuries. Yet the dangers of pursuing reparations without faithfully pursuing the third element of repair are great, as African-Americans risk perpetuating American social hierarchy by reshuffling the players without dismantling the game. To be clear, I am not the familiar dissenter in reparations debates.3 I do not believe that reparations claims are without basis. In fact, in light of the centuries of indignities suffered by African-Americans, reparations are absolutely warranted.4 I instead seek something qualitatively different from what many of the most enthusiastic reparations proponents advocate. I am seeking reconciliation-and a concomitant guarantee of nonrepetition-through profound social change. In Part I, I briefly survey the history and contemporary claims of the African-American reparations movement. I then evaluate the viability of the current reparations paradigm, foregrounding the peculiarly individualistic and historically prejudicial American context within which those claims are brought. I seek to highlight the characteristics of the American political economy on which current claims rely, but which are themselves vital targets for effective reparations. In Part II, I argue for a redefining of the African-American reparations movement, focusing on a restructuring that can meet the mandates of nonrepetition. I look to the Japanese-American reparations campaign and argue that the Japanese-American experience provides not a model for emulation, but a crucial cautionary tale. The failure to address nonrepetition in obtaining reparations reinforces the political, social, and economic status quo. In Part III, I expand upon the potential dangers of reparations pursued within the current paradigm and argue that the most important failing of the contemporary reparations struggle is its limited scope. A limit in scope indicates dwindled optimism about fashioning an alternative future. This diminished optimism has serious consequences: as John Torpey poignantly declares, "[w]hen the future collapses, the past rushes in.",5 I conclude by arguing for the infusion of a grander vision of social justice in African-American claims, and by advocating for an alternative reparations campaign focusing on structural change. My purpose here is not to prescribe a particular roadmap for meeting the mandates of nonrepetition, although I do offer some suggestions. Instead, my aim is to initiate a discussion among African-American reparationists that will shift the focus to the vital need for a movement centered on nonrepetition. Indeed, a fundamental ideological shift in the movement is essential to repair the very brokenness inextricably interwoven in the American cultural machine-a brokenness that produces and reproduces the economic and racial subjugation on which this country has historically depended for its prosperity.

This brings us to what we take to be the real disagreement between Atkinson and ourselves: the politics of PI. In our 2007 article we stipulated that in the trilemma we can avoid only two of three horns—that is, reverting to soft workfare or by contrast, fully embracing an unconditional BI—by accepting a third, the need for intrusive and costly ‘iron-clad administration’. In his second response to our trilemma, Atkinson claims that faced with this trilemma, he would accept the need for more administration, something which he contends is desirable more generally. Reiterating a major theme outlined earlier in Inequality, he insists ‘the state should invest in better social administration, recognising that this requires a higher labour input, and emphasising the quality of service rather than merely measuring cost efficiency.’ 11 Furthermore, he argues that since PI does not involve means-testing, its introduction would free up considerable administrative resources that could be reassigned elsewhere in the system. In our view, it is unlikely that policy would take this turn in the short run, given current governments’ focus on budget restraint and cost-containment following the 2008 Great Recession. If political feasibility is one of the criteria for accepting a particular choice, then embracing iron-clad administration is, for the time being, a non-starter.2

However, our disagreement with Atkinson is grounded in a deeper concern. We share Atkinson’s personal preference for investing in administrative capability to accommodate PI implementation challenges. But it is in fact precisely that—a personal preference. What Atkinson fails to appreciate when responding to our trilemma in this manner are the administrative challenges to instituting PI —and the hard choice of how to accommodate them at the level of implementation. All of these are bound up with the coalitional politics of trading-off competing policy goals in a political environment where deep disagreement persists about both the goals and the instruments of income support. The point is not whether Atkinson—or we—have good reason to opt for one or other way out of the trilemma; rather, the issue is that in the political climate in which PI is presented as a solution to the challenges of instituting an unconditional BI, the trilemma drives a wedge between different political factions, each of which supports PI for different reasons.

Twenty years ago, Tony Atkinson suggested that because ‘it will be difficult to secure political support for a Citizen’s Income while it remains unconditional on labour market or other activity’, a compromise might be required. He thought that political support would be easier to achieve if receipt of an otherwise unconditional and nonwithdrawable income were to be conditional on some kind of participation in society.Footnote15 As Tony Fitzpatrick has put it: such a ‘Participation Income’ would require participation in society, which might be more acceptable to the public and to policymakers than an income that simply invited it.Footnote16

The ‘Participation Income’ would be given to people who were ill, disabled, retired, or looking for work, without their having to ‘participate’ in any other way, but otherwise at least one of a number of participation conditions would need to be met. Employment, self-employment, education, training, voluntary work, and caring for the young, older people, or disabled dependents would all count as participation in society.

Critics might be tempted to conclude that debating PI has become redundant at a time when a fully unconditional basic income appears to be gaining ground with decision makers and the general public alike. If, two decades ago, interest in PI was justified primarily by an urgent need to reform meanstested benefits at a time when unconditionality was deemed an insurmountable political barrier, many would argue it has become obsolete now that governments across Europe are on the verge of experimenting with schemes to make the basic level of unemployment assistance unconditional. To be sure, this is merely a first step, but an important one nonetheless: it opens up the possibility of introducing basic income at very modest levels rather than taking the roundabout way of the PI approach.

Leaving aside the question of whether existing levels of support for basic income are sufficient to build a robust coalition, we want to focus briefly on the idea of basic income as a complement to existing social security schemes. In his 1996 article, Atkinson wrote:

Atkinson’s first response to our trilemma amounts to denying the scale of the difficulties we identified. His main reason for this lies in the supposition that PI could piggyback on existing welfare administration. For example, Jobseeker’s Allowance (JSA) currently allows claimants to restrict their hours of work availability due to caring responsibilities. Similarly, certain types of voluntary work allow them to postpone taking up a job offer. PI would thus rely on categorical distinctions that are already familiar and widely used in current social protection schemes. While Atkinson is very alive to the complex and stigmatising administration of means-testing, he appears, in contrast, to believe that eligibility testing for programmes that only require category decisions is relatively straightforward— and would reap the administrative savings of avoiding the more challenging task of means-testing.Atkinson’s first response to our trilemma amounts to denying the scale of the difficulties we identified. His main reason for this lies in the supposition that PI could piggyback on existing welfare administration. For example, Jobseeker’s Allowance (JSA) currently allows claimants to restrict their hours of work availability due to caring responsibilities. Similarly, certain types of voluntary work allow them to postpone taking up a job offer. PI would thus rely on categorical distinctions that are already familiar and widely used in current social protection schemes. While Atkinson is very alive to the complex and stigmatising administration of means-testing, he appears, in contrast, to believe that eligibility testing for programmes that only require category decisions is relatively straightforward— and would reap the administrative savings of avoiding the more challenging task of means-testing.

However, this ignores the many ways in which current benefit administration already fails—often disastrously so, at least viewed from the perspective of the claimant encountering refusal, delay or sanctions. Consider, for example, the increased manifestation of ‘hidden conditionality’ in the recent reform of disability benefits in the UK, which has a debilitating and stigmatising impact on disabled claimants and in many cases pushes them further into poverty and dependency.8

The first horn of the trilemma consists of the requirement that PI must remain substantively inclusive if it is to satisfy the concerns of basic income advocates. The second horn is represented by the equally important requirement, insisted upon this time by reciprocity theorists and soft workfare proponents, that recipients must satisfy a genuine participation requirement. Such a requirement in turn demands that any PI scheme must be capable of differentiating between those who fulfil their social obligations, however defined, and those who do not. Finally, the third horn is made up of the ... concerns that pertain to the economic and human costs associated with administrability. The trilemma arises because PI can only avoid two of three horns simultaneously. The scheme inevitably gets pinned on a third.3

In developing our response to Atkinson, we must first recall why the trilemma arises. Our claims are grounded in the essential features of a control system as elaborated in the administrative cybernetics literature, namely setting standards, gathering information on compliance with those standards, and modifying behaviour.4

To be sure, simply removing the participation requirement and moving from a modest PI to a modest UBI might not on its own have much effect on the distribution of care work, although any relative increase in the economic resources of carers compared to workers should increase carers’ bargaining power in negotiations over the division of labour within the family or household. But in addition to implementing a selective reciprocity, the PI implements a selective conditionality as well. The ‘participation’ requirement disadvantages those with comparatively little income or wealth, for whom declining to ‘participate’ has much more serious consequences than it does for those with comparatively more: those with sufficient capital are free from the need to document the social utility of their daily activities while those without capital must do so in order to survive. This selective conditionality implicitly endorses the basic legitimacy of the status quo distribution of income and wealth as being based on merit.

In contrast, the principle of unconditionality recognises that many of us are free-riding ‘surfers’ in any number of ways: as direct or indirect beneficiaries of the unpaid care and other voluntary work that sustains and reproduces our families and communities, or as individual beneficiaries of our collectively enforced rights to private property ownership and inheritance, or as recipients of unearned ‘rents’ we collect through protected first-tier employment, luck-driven endowments at birth, or our places in economic and political power structures. Because our relative incomes and wealth are due at least in part to these forms of free-riding, a ‘participation’ requirement that is not universal, but selectively imposed on those who require cash assistance to meet their basic needs, improperly implies that high income and wealth is a proxy for ‘participation’ that obviates the need for any further monitoring.13 Once again, a gender perspective makes this problem clear: women are disproportionately represented at the lower end of the income and wealth distributions,14 and thus disproportionately subject to the conditionality of the PI. Can it really be the case that women as a class contribute less to society than men do and thus require more monitoring of their social contributions than men?

Dark matter is one of the biggest mysteries in all of modern science. Everywhere we look on large cosmic scales — from low-mass galaxies to the largest galaxy clusters, from the cosmic microwave background to the cosmic web that traces the Universe's structure — we can see the imprints and effects of its presence. For every proton's mass worth of normal matter, there's five times as much dark matter, out-massing and out-gravitating the conventional stuff that makes up everything we've ever directly detected. Even though we have yet to directly detect it, and even though we aren't sure exactly what its true properties are, dark matter holds a tremendous promise for the future of humanity. Ubiquitously located all throughout the galaxy and far beyond, dark matter could be the perfect fuel that makes our interstellar dreams come true. Here's the story of how. A logarithmic chart of distances, showing the Voyager spacecraft, our Solar System and our nearest... [+] star, for comparison. If we ever hope to travel across the great interstellar distances, it will require a technology that's superior to chemical-based rockets, and hopefully that will include the discovery of a fuel that can be replenished as we traverse our path through the galaxy. Whenever humanity sets our sights on exploring the depths of space, there are constraints we can't avoid: the laws of physics. In order to accelerate a spacecraft — or any mass — you have to impart an impulse to it in order to change its momentum. The larger the impulse, the more you can change an object's speed. All that determines the magnitude of an impulse is how much force you apply and how long you apply it for. In a conventional rocket, that impulse is provided by rocket fuel that undergoes a combustion reaction, which produces impulse in the form of thrust. Although this is the best method humanity has come up with for space travel so far, it's incredibly limiting. All of our past and current rockets are chemical-based, unfortunately, and that places tremendous constraints on how far we've been able to go. This 2015 engine test shows the firing of SpaceX's Raptor engine, which relies on an extremely... [+] powerful and fuel-efficient reaction. Unfortunately, it's still a chemical-based reaction, and converts only about one-millionth of the fuel's mass into energy. We will have to do better if we want to achieve our interstellar dreams on timescales of a human lifetime. The reason for this is simple: in order to produce thrust — i.e., in order to impart an impulse to your spacecraft — you have to convert that stored chemical energy in the fuel into kinetic energy that pushes your spacecraft. In order to generate that energy, however, you have to use up some of that fuel you're carrying with you. The key to getting lots of thrust, and therefore lots of acceleration, is fuel efficiency. Certain types of fuel are more energy-efficient than others, meaning that we can get more energy (and thrust, and acceleration) out of, say, 1 kilogram of some types of fuel. An easy way to think about this is through Einstein's most famous equation: E = mc2. If you had a perfect, ideal fuel, it would convert 100% of your fuel's mass into energy, enabling you to make the most efficient fuel imaginable. The launch of Cassini, on October 15, 1997. This spectacular streak shot was taken from Hangar AF on... [+] Cape Canaveral Air Force Station, with a solid rocket booster retrieval ship in the foreground. For all of our history on Earth, the only way we've ever reached space is through the use of chemical-based fuels. At most, though, chemical-based reactions are somewhere around 0.0001% efficient. The reason is as follows: chemical reactions rely on electron transitions between atoms and molecules. Most of an atom's mass is in the form of protons and neutrons, each of which have a mass that contains around 109 eV worth of energy. Electron transitions, however, are on the order of a few (typically 1-10) eV of energy. Even with all the chemical-based tricks we can perform, there are no known reactions that allow us to improve on this. Sure, we can go for some type of nuclear fuel, but that's only marginally better, achieving efficiencies of around 0.1%. It's a huge improvement, if we can realize it, but there's still a fundamental problem with accelerating to speeds that will carry you interstellar distances on reasonable timescales. The Tsiolkovsky rocket equation is required to describe how fast a spacecraft that burns through a... [+] portion of its fuel to create thrust can wind up traveling through the Universe. Having to bring your own fuel on board is a severely limiting factor as far as the speed at which we are capable of traveling through intergalactic space. Skorkmaz at English Wikipedia The key problem is as follows: whenever you burn fuel, you have to accelerate the entire mass of your spacecraft, including any fuel that's still on board. Read that again: including any fuel that's still on board. In other words, let's imagine you can shoot exhaust out of your vehicle at an incredible rate: 100,000 mph (about 160,000 kph), relative to the rocket itself. If you start off with a rocket where 99% of your initial mass is fuel, and you assume that your fuel is perfectly 100% efficient (as though it were pure matter-antimatter annihilation), you'd wind up with a final speed of 460,000 mph (740,000 kph). Even at this record-setting rate, it would still take thousands of years to reach the nearest star. All rockets ever envisioned require some type of fuel, but if a dark matter engine were created, new... [+] fuel is always to be found simply by traveling through the galaxy. Because dark matter doesn't interact with normal matter (mostly) but passes right through it, you wouldn't have any difficulty collecting it in a specific volume of space; it would always be there as you moved through the galaxy. On the other hand, there's another approach to interstellar travel that could — in principle — make our science-fiction dreams come true. Instead of bringing your fuel with you, what if you collected it as you went? Typically, ideas like this involve enormous magnetic fields that funnel charged particles into some sort of "trap" in your spaceship, allowing you to put nuclei and electrons together where you can then extract energy and perform further reactions with them. But dark matter offers a tremendous advantage over normal matter in this regard. Why? Because you don't have to do anything special to collect it. It's literally everywhere, distributed in an enormous halo surrounding and encompassing every large galaxy we know of, including the Milky Way. If we find ourselves anywhere in the galaxy, there's bound to be dark matter lying around. While stars might cluster in the disk and the normal matter might be restricted to a nearby region... [+] around the stars, dark matter extends in a halo more than 10 times the extent of the luminous portion. It is truly found everywhere humanity has dreamed of traveling in our own galaxy, and in many places beyond. The second tremendous advantage comes from the progression away from chemical-based rockets and towards the idea of a perfect fuel. For chemical-based rockets, 0.0001% energy efficiency is the best we can hope for. For nuclear-based rockets, fission power might get us up to 0.1% efficiency, and nuclear fusion might get us a little further: perhaps up to 0.7%. The ideal configuration would be to use matter-antimatter annihilation, which is 100% energy efficient. The downside of matter-antimatter annihilation comes with a terrible cost, though: it takes a tremendous amount of work, energy, and effort to create an extraordinarily small amount of antimatter. If you took all the particle physics laboratories ever constructed on Earth and added up all the antimatter humanity has ever created, from Fermilab to CERN, you'd wind up with less than a microgram of antimatter. A portion of the antimatter factory at CERN, where charged antimatter particles are brought together... [+] and can form either positive ions, neutral atoms, or negative ions, depending on the number of positrons that bind with an antiproton. If we can successfully capture and store antimatter, it would represent a 100% efficient fuel source, but many tons of antimatter, as opposed to the tiny fractions of a gram we've created, would be required for an interstellar journey. Sure, E = mc2 might be the most efficient way to extract energy from mass in the entire Universe, as it represents perfect efficiency. But even if you manage to contain and store your antimatter successfully and annihilate it only at the proper moment, you'll still have a finite supply of fuel that required an incredible amount of energy to collect. Once you use up this perfect fuel, you're all out, and all you can do is travel at a constant velocity through space for an indefinite duration of time. Even if we could generate an arbitrary amount, we'd still be fundamentally limited with an antimatter rocket. That's why the promise of a dark matter fuel source is so alluring. Not only might dark matter be an unlimited fuel source (in terms of abundance) that we don't have to carry on board with us, but it might have that perfect, 100% efficient matter-to-energy conversion potential we so strongly desire. Our galaxy is thought to be embedded in an enormous, diffuse dark matter halo, indicating that there... [+] must be dark matter flowing through the solar system. Although we have yet to detect dark matter directly, its abundant presence throughout our galaxy and beyond might provide a perfect recipe for the perfect rocket fuel imaginable. Robert Caldwell & Marc Kamionkowski Nature 458, 587-589 (2009) There are a multitude of experiments looking for the collisions of dark matter with both normal matter and itself. In general, there are two types of particles in the Universe: fermions (with half-integer spins) and bosons (with integer spins). If dark matter is a bosonic particle with no electric, color, or weak charge, that would mean it behaves as its own antiparticle. If you can collect two dark matter particles and make them interact with one another, there's a finite probability that they'll annihilate. When an annihilation occurs, they'll produce pure energy in a 100% efficient fashion: via Einstein's E = mc2. In other words, if we understand dark matter correctly, there's a free, unlimited source of energy everywhere humanity dreams of going. The XENON experiment located underground in the Italian LNGS laboratory. The detector is installed... [+] inside a large water shield; the building next to it accommodates its various auxiliary subsystems. If we can understand and measure the particle properties of dark matter, we may be able to create conditions that coax it into annihilating with itself, leading to the release of energy via Einstein's E=mc^2, and the discovery of a perfect spacecraft fuel. Because dark matter is everywhere, we wouldn't even need to carry it with us as we traversed the Universe. As far as we understand it — and admittedly, we need to understand it a lot farther — dark matter could truly deliver our dream of the ultimate fuel. It's abundant all throughout our galaxy and beyond; it should have a non-zero annihilation cross-section with itself; and when it does annihilate, it should produce energy with 100% efficiency. Perhaps, then, most of us have been thinking about experiments seeking to directly detect dark matter all wrong. Yes, we want to know what makes up the Universe, and what the physical properties of its various abundant components truly are. But there's a science-fiction dream that could come true if nature is kind to us: unlimited, free energy just waiting there for us to harness, no matter where in the galaxy we go. Mastering dark matter is the endeavor that just might make it so.

The study of time is a somewhat barren field. It became the focus of many scientists after Einstein bound the concept of time to the concept of space (creating spacetime). However, physicists have found it challenging to probe further into how time works. But one physics professor is stating his mind when it comes to time. Professor Richard Muller of UC Berkeley has published NOW: The Physics of Time, which explains his view of how and why time flows. It all started with one question: Why does the arrow of time flow inexorably toward the future, constantly creating new “nows”? Muller's theory on the flow of time merges two ideas: the expansion of the universe, and the concept of spacetime. The universe is expanding, but not because the stars are flying away from each other. Instead, the fabric of spacetime is expanding, while the stars stay put. Just let that sink in a moment. Space has been expanding ever since the Big Bang. Muller theorized that, as space is expanding in the universe, so is time. “Every moment, the universe gets a little bigger, and there is a little more time, and it is this leading edge of time that we refer to as now,” he writes. STUCK IN THE PRESENT This concept has some interesting consequences. First, it invalidates travel to the future, since there is actually no future yet to travel to. Travel to the past is also next to impossible, since you would have to destroy some space in order to turn back time. This does occur when a black hole evaporates or a star explodes, but the impact is so small that it wouldn't matter. Essentially, Muller is killing all of your childhood science fiction dreams. Muller's theory even led to a collaboration with Caltech theoretician Shaun Maguire and a paper that proposes a way to test the theory using LIGO. If the scientists are right, then when two black holes merge and create new space, they should also create new time (one millisecond, to be exact) which would delay the gravitational wave signal LIGO observes from Earth. Muller is optimistic that in the next few years LIGO will verify or falsify his theory. “I think my theory is going to have an impact on calculations of the very early universe,” Muller said. “I don’t see any way that it affects our everyday lives. But it is fascinating.”

The team at the University of Cambridge, however, monitors energy on a more extreme level as they try to approach absolute zero—the coldest temperature allowed by the laws of thermodynamics. Absolute zero, technically known as zero kelvins, equals −273.15 degrees Celsius, or -459.67 Fahrenheit, and marks the spot on the thermometer where a system reaches its lowest possible energy, or thermal motion. There’s a catch, though: absolute zero is impossible to reach. The reason has to do with the amount of work necessary to remove heat from a substance, which increases substantially the colder you try to go. To reach zero kelvins, you would require an infinite amount of work. And even if you could get there, quantum mechanics dictates that the atoms and molecules would still have some irreducible motion. Quantum mechanics also means that the closer these researchers creep toward absolute zero, the weirder a substance’s properties become. At low enough temperatures, liquid helium, for example, morphs into a superfluid—a liquid that flows without the resistance of friction. As a result, it can spontaneously flow upwards and out of a container; seep through molecule-thin cracks; remain perfectly still while spinning at high speeds; and—most surprising to physicists—coalesce into one “super-atom,” known as a Bose-Einstein condensate. Working at around just 1 to 10 millikelvins, or thousandths of a kelvin, the Cavendish team is in the process of surveying a variety of other materials that also show funky quantum behavior. And the technology that the group uses to reach such frigid temperatures is almost as complicated as the behavior it’s trying to induce.

BROOKS: People always want us to fight, but we don't really. I think, although I agree with the general themes that Andy talks about, I think it's very easy for people who are not deep in the technology itself to make generalizations, which may be a little dangerous. And we've certainly seen that recently with Elon Musk, Bill Gates, Stephen Hawking, all saying AI is just taking off and it's going to take over the world very quickly. And the thing that they share is none of them work in this technological field. So let me explain why—and they're all smart people, but I think they're making a fundamental error and it gets to NEIL, actually. THOMPSON: After taking down Bill Gates, Elon Musk and Stephen Hawking, he's going to take down the Dalai Lama. Please continue, Rodney. BROOKS: So let's go back to an example from the '90s, when IBM's Deep Blue beat Kasparov, beat the world chess champion. And Kasparov got up and said, well, at least it didn't enjoy beating me. That was his—holding on to his humanity. And now, today, you can get programs that run on—and that was on a supercomputer and now you can get programs that run on laptops. There's about twelve of them that have a better chess rating than any human being has ever had. So people see that -- MCAFEE: It's so bad now—let me underscore what Rod is saying. It's so bad now that they asked human grand master a couple years ago how he would prepare for a match against a computer and he said, I'd bring a hammer. BROOKS: So they can play chess really, really well. And I think people generalize that in the way that if a person can do some task really, really well, they can do adjacent tasks quite well. But none of those chess programs can play tic-tac-toe. Imagine a chess grand master who couldn't play tic-tac-toe. It doesn't make sense. None of those chess programs can give advice to an aspiring human on how to play better. All they can be is a sparring partner. MCAFEE: That program couldn't play tic-tac-toe without being substantially redirected, right? BROOKS: Right. So people, I think, are seeing some of the image labeling that's going on, for instance. Google came out with image labeling, which is a great commercial problem for them. They want to be able to label images. And one of the examples was, that Jeff Hinton shows, one of the chief scientists, is, it's a picture and it says there's a baby holding a teddy bear or doll in there. You look at it, it's a baby holding a teddy—a doll. But then if you ask the program, where is the baby? All it can say is, well, this pixel has 10 percent probability of being a baby, this pixel has 80 percent. And people have done experiments. You have a mashup of, you know, a grotesque mashup of baby parts and it says it's a baby. It's a baby. It's got all the parts. But a person says, no, that's a grotesque mashup of baby parts in the image. THOMPSON: But Abhinav, you've solved this, right? GUPTA: No, no, no. BROOKS: Well, he's working towards-- GUPTA: So, can I-- BROOKS: He's working towards it because it's such a hard problem. GUPTA: Yeah, OK. Thank you. So since we are talking about images, I think I should chime in a little bit and tell you that—so what Andrew is talking about, that we have made big advances, again, they're very, very specific tasks. Given an image, tell me what label can you put on that image? We have gotten really good at this task. Some people claim even better than humans. I don't buy that, but let's assume that even better than humans. But that doesn't mean we can do anything else apart from that exact task. And that's what Rodney was talking about. They have no idea that—what does baby mean? What does having a baby mean in those images? No idea. You, as a human, would know, OK, if I'm saying there's a baby, it has a lot of meaning inside. You get a lot of meaning out of that thing. So while we have made significant advances in the last two years, I want to boil it down a little bit and say we still are a long, long way to go but Elon Musk or Bill Gates, everyone is talking about, we still have a long way to go. But there's hope, and that's what I think we have to see here. Two years ago, if you asked me can computers take an image and solve this problem, I would say I have invested seven years of my life but if you give me a random image, it will not work. And now, given a random image, it will work. So all it -- MCAFEE: This was the guy who was doing this for a living and if you asked him two years ago would this happen, he would say, no. This progress is weirdly fast and is surprising insiders in the field. GUPTA: Yeah. I agree. And I'm an insider in the field and I'm very surprised, I have to say. Now, at this point of time, I am like living in an awe of myself, in some sense, that—but it was like Rodney told—Rodney told us that in thirty-five years he never thought he'd do this all. I also thought some of it, like that, for thirty-five years, I will not solve—see this kind of classification performance. But as I'm saying this, still a long, long way to go and much harder way to go. What—where all the kind of gains have come from is the data. And I think—so technology, this like deep-learning technology has been there from '70s and '80s. Don't misunderstand that this technology came two years ago and everything's changed. This has been there for thirty years. It's just that for the first time in our technological advances we have data for this deep-learning technology to learn. MCAFEE: Let me jump on this because I think the three of us are really agreeing, instead of disagreeing. I chose my adjective pretty carefully. I said these advances are going to be economically significant. I completely agree with Rod that they're not going to be existentially significant on any timeframe that we really need to worry about, for exactly the reasons that you're bringing up. One way to think about this, the way I try to get my mind around it, is there are, from what I've been able to take in, there are something like between ten and twenty really fundamental challenges that these guys and their discipline have been working on. Common sense is a really great example of that. As I've looked around, these breakthroughs that we're seeing seem to be—kind of indicate that we're making real progress on one of those challenges, the challenges of learning in a pretty unstructured environment. That's a big deal. There are lots of other fundamental challenges in the discipline where the progress has not been as fast, and these are the ones that you're working on.

There are ways to mitigate the actual dangers//// Given that most objects that will be manipulated into crawling, flying, and replicating machines will be at or above the nanoscale (and not atomic in scale, or even remotely close), there are definitely going to be numerous people working to deal with the threat of "runaway" nanotech. Nanobots would need to be self replicating in order to be effective on any massive scale, and as such, nano-factories will have to be contained, protected, and have an external computer and power source. An external power source would limit the potential for "swarms" to escape into the real world. Further, the alarm bells have been raised by Hollywood and the popular press. It's highly unlikely that any sort of large scale nanotech design will slip past media scrutiny.//// In addition (and perhaps most importantly), nature has its own built-in self regulation mechanism. Here's Mike://// "Simple: Bacteria will eat them. Microbes are nanobots with a billion years of refinement. They are very good at eating things made of graphene and nanotubes, and working with the limited energy and resources available in their environment. This is why nanobots work best in a controlled environment - they're very useful, but couldn't survive in the wild." Special shout to daelyte on reddit for the original idea of bacteria as nature's defense mechanism, too.//// If extremely small scale, self-replicating robots indeed prove to be feasible, cosmic rays from space, simple terrestrial wind, organic bacteria, and other naturally occurring evolutionary defense mechanisms on planet earth (including Brownian motion!) will be fully capable of tearing apart "nanobots" at the atomic scale all on their own.//// Conclusion//// The bottom line: the amazing things we can do with nanotechnology - from hidden sources of energy, to very small devices in our bloodstream capable of policing our immune system, to Drexler's "factory in a box" idea - will far outstrip the potential risks, particularly with nature's built in mitigation system, and with a tremendous amount of care and concern. The media tends to play on our darkest (and most unlikely) fears becoming a certain reality, and nanotech is no exception.//// Here's Mike to wrap things up:."

In 2004, the Royal Society and Royal Academy of Engineering (RS-RAE) in the UK published the report Nanoscience and Nanotechnologies: Opportunities and Uncertainties1. At the time it was widely speculated that the report arose from concerns expressed by Prince Charles over the possibility that nanotechnology could lead to a ‘grey goo’ scenario where self-replicating ‘nanobots’ destroy life as we know it2. Outlandish as the alleged motivation was (and Prince Charles was quick to downplay reports of his grey goo concerns3), the resulting report set the pace for the next decade of global research into the potential impacts of nanotechnology — and how to avoid them. //// Around the time the report was commissioned, concerns over the potential unanticipated consequences of nanotechnology were beginning to gain wider traction4. Essays like Bill Joy’s ‘Why the future doesn’t need us’5 were raising concerns in the public domain, and professional interest in possible human health and environmental impacts of nanoscale science and engineering had been growing steadily for the previous decade. As far back as 1992, for example, the journal Nature published a Correspondence raising the issue of possible asbestos-like behaviour of carbon nanotubes6 — less than a year after Sumio Iijima published his seminal work on the structures7. And during the 1990s, particle toxicologists began revealing increasingly unusual biological interactions associated with certain nanoscale particles8. //// During this period, the US and other countries were beginning to invest heavily in nanoscale science and engineering as an engine of economic growth9. Alert to a potential public backlash against the technology that could undermine this public investment (nanotechnology at this point was riding hot on the heels of a widespread European rejection of genetically modified foods), research agencies began investing in the possible implications of nanotechnology10. In the US, the National Nanotechnology Initiative pulled together expertise on the possible impacts and benefits of the new technology11, and health and environmental impacts were integrated into the country’s national research and development strategy12. It was, nevertheless, the RS-RAE report that emerged as the defining document for research into the potential impact of the field. //// The report was ostensibly focused on evaluating both the opportunities and uncertainties of nanotechnology. Under the leadership of Professor Dame Ann Dowling — head of the Department of Engineering at the University of Cambridge — a select working group of experts from multiple fields set out to define what is meant by nanoscience and nanotechnologies; to summarize the current state of knowledge; to identify specific applications; to carry out a forward-look to see how the technologies might be used in the future; to identify what health and safety, environmental, ethical and societal implications and uncertainties might arise; and to identify areas where additional regulation needed to be considered. The working group received input from over 200 experts in nanotechnology development, use, safety, ethics and governance from around the world. Based on this input, and their own expertise, the group produced arguably the most comprehensive and accessible assessment of nanoscale science and technology at the time. //// Despite their broad remit, however, the working group skipped over the many potential benefits of nanotechnologies in their recommendations, and focused almost exclusively on the potential risks and uncertainties. Of the 21 recommendations arising from the report, 19 of them addressed potential implications of the emerging science and technologies. Some of the recommendations were specific to UK investment in nanotechnology at the time, but others responded directly to the global dearth of knowledge on potential risks alongside hints of potentially harmful behaviour. The message was clear: whatever you might think about the economic and societal benefits of this new suite of technologies, extensive further investment into possible applications would be foolish without direct investment in research and action on potential implications. //// Since 2004, peer-reviewed publications addressing the health and environmental impact of engineered nanomaterials have skyrocketed. A search of the nanoEHS Virtual Journal13 (a database of articles related to the environmental and health impacts of nanotechnology that have been published in different journals) returns 139 peer-reviewed papers related to nanomaterial risk published in 2003; the same search returns 1,326 papers published in 2013, with a rapid increase in the rate of publication occurring in 2006 — just two years after the RS-RAE report (Fig. 1). Although it would be disingenuous to suggest that this increase was solely due to the report, the document clearly stimulated global movement towards investing more heavily in research around potential health and environmental implications of engineered nanomaterials. //// The result of this investment is an understanding of the impacts of nanotechnology that extends further than anyone might have imagined in 2004 14. An extensive body of published data on the human and environmental impacts of mainstream metal and metal oxide nanomaterials now exists, and recent research has shed important light on the potential health effects of carbon nanotubes15,16 — a field that was all but ignored between 1993 and 2004. Global-risk-research approaches for nanoscale materials have been addressed by a number of organizations, including the Organisation for Economic Co-operation and Development17. And chemical safety regulations in the US, the EU and Australia have been evaluated with respect to their applicability to engineered nanomaterials18. //// Although this has been a global effort, there is no doubt that the RS-RAE report was a catalyst for action: a voice of scientific reason and social concern at a time when speculation could have scuppered the nanotechnology enterprise or, worse, led to materials and products that showed a blatant disregard for health and environmental risks. But the report’s legacy is more complex than this. As research into the health, environmental and societal implications of nanotechnologies has grown, the relevance of this research has become less clear. Spurred on by fears of novel and unique behaviour, millions of dollars have been invested into the risk research of materials that — although they show toxicity at high exposures — don’t always seem to hold the dramatic risk surprises that some thought they would. This isn’t always the case — carbon nanotubes again stand out as a material that needs to be used with caution. Yet substances like silver, titanium dioxide and cerium oxide nanoparticles are failing to show unambiguous indications of substantial and unusual health and environmental impacts, encouraging researchers to dig ever-deeper to discover the assumed-to-exist evidence of novel risk. //// This is the darker side of the RS-RAE legacy — and one that probably could not have been anticipated. Legitimate questions were asked by the RS-RAE working group over what could possibly go wrong with these new, and esoteric, materials. But this set the global risk research and regulation community on a path that has, over time, worn a rut that is proving hard to get out of. The speculation of possible risk has developed into an assumption of as-yet-to-be-discovered risk. //// This is not to say that there are not significant risks associated with nanoscale materials — as research continues to show, nanoscale materials can and do interact with biological systems in unusual ways. Yet by focusing on only a small group of materials that grabbed headlines early on, researchers run the danger of missing emerging materials and products that may present greater challenges than those initial nanoscale materials. //// Ten years ago, the RS-RAE working group admirably turned speculation over grey goo into a solid foundation of an evidence-based approach to plausible nanoscale material risks and realistic risk avoidance strategies. Today, amidst the undeniably important progress that has been made following the report, it has to be wondered whether researchers have created a new, metaphorical grey goo in their quest to respond to speculative nanomaterial fears. If so, maybe it’s time to once again use speculation as a lever to shift research and action on risks and benefits towards evidence-based approaches to the next generation of advanced materials and products emerging from nanoscale design and engineering.

The creation of black holes at the Large Hadron Collider is very unlikely. However, some theories suggest that the formation of tiny 'quantum' black holes may be possible. The observation of such an event would be thrilling in terms of our understanding of the Universe; it would also be perfectly safe. Two types of black hole Black holes form in space when certain stars, much larger than our Sun, collapse on themselves at the end of their lives. They concentrate a very large amount of matter in a very small space. They are so dense that the gravity they exert is such that not even light can travel out of them. Speculations about black holes at the LHC refer to particles produced in the collisions of pairs of protons. These are microscopic - or quantum - black holes. Scientists are not at all sure that quantum black holes exist. Nature's experiment A computer-generated image showing the detection of a microscopic black hole A simulation of a quantum black hole detected by the ATLAS experiment, before it decays via a process known as Hawking radiation. » see larger version on the CERN Document Server The physical part of the LHC experiments - colliding particles - happens in nature all the time. We know, for example, that the Earth is constantly bombarded by cosmic rays: when cosmic rays hit the atmosphere, particles are colliding with one another in much the same way as in the collisions planned at the LHC. Just as we know that the Earth is safe under the natural bombardment from cosmic rays, so we know that recreating these collisions poses no threat to the Earth. Nature’s collisions also reach much higher energies than those at the LHC. What if collisions at the LHC produced a black hole? The creation of a quantum black hole at the LHC would be very surprising, but very exciting indeed. It would allow physicists to learn about nature’s most elusive force – gravity. Remember: particle collisions happen all the time in nature, and we're all still here. If you would like to read up more on the safety of the LHC, there is more information here. What would be the significance of the creation of a black hole at the LHC? The creation of a black hole at the LHC would confirm theories that our universe is not 4 dimensional (3 space plus 1 time dimensions), but indeed hosts other dimensions. It would be quite a spectacular philosophical outcome! In the same way that the theory of relativity or of quantum mechanics revolutionized our way of thinking, discovering the existence of extra dimensions would be a major new milestone in our understanding of the Universe. There is no obvious application for knowing this. Many people will start speculating about using these extra dimensions for space and time travel, or as a source of clean energy, and who knows what else. It is rather tempting to compare it to the discovery of magnetism by the Phoenicians who could not foresee that electricity and magnetism would completely reshape modern life...

Another way of revealing extra dimensions would be through the production of “microscopic black holes”. What exactly we would detect would depend on the number of extra dimensions, the mass of the black hole, the size of the dimensions and the energy at which the black hole occurs. If micro black holes do appear in the collisions created by the LHC, they would disintegrate rapidly, in around 10-27 seconds. They would decay into Standard Model or supersymmetric particles, creating events containing an exceptional number of tracks in our detectors, which we would easily spot. Finding more on any of these subjects would open the door to yet unknown possibilities.

One of the places that personifies all of this is the Large Hadron Collider (LHC) at CERN, where in the next few months, we’ll begin colliding protons at the highest energies ever achieved in a particle accelerator. A few years ago, we broke the old record — 2 TeV (tera-electron-Volts, or 10^12 eV), which was set at Fermilab — by accelerating each particle up to 3.5 TeV and smashing them into one another, achieving 7 TeV of total energy.//// This discovery enabled us to not only create huge numbers of a great many elusive, fundamental particles (like the top quark, as well as the W-and-Z bosons), but enabled us to discover a brand new fundamental particle and last undiscovered particle in the standard model: the Higgs boson. //// Later this year, upgrades to the LHC will enable us to reach somewhere between (depending on whom you ask) 13-and-14 TeV of total energy. If we’re really lucky, the sheer number of collisions at these tremendous energies, combined with the incredible detectors we have in place, may allow us to create and discover never-before-seen particles in this laboratory. //// Of course, that hasn’t stopped the usual suspects from making incredible (and completely non-credible) claims, such as: //// , , and That may . While the first two are just bad science reporting, the third one is a common fear that’s reared its ugly head time and time again, and has no basis in reality. //// So what’s the big idea, and how do we know it’s wrong? Let’s find out. //// There are a number of theories that predict the existence of extra dimensions. Not merely the three spatial and one time dimension we know to be present in our four-dimensional spacetime, but at least one additional spatial dimension that exists in our Universe. While we can’t quite access those dimensions at the energies we’ve probed, it’s conceivable that at scales that are smaller than those we’ve examined — which corresponds to higher energies — these extra dimensions exist. //// And if these extra dimensions exist, one theoretical possibility is that it might be possible to create tiny, miniature, microscopic black holes! //// If we could do this, this would be an incredible feat of technology, of science, and an amazing piece of evidence that would change our understanding of the Universe forever. Of course, however, you say the words “black holes” and people immediately get this catastrophic picture of something sucking in all sorts of matter, progressively eating the protons, neutrons and electrons that make up our world, and eventually destroying the entire thing. //// This is not possible. In fact, there are three reasons we know this is not possible. Let’s go over them one at a time. //// 1.) If these miniature black holes exist, the Earth has been getting hit by them for billions of years, and it’s still here. //// Sure, we’ve never created particles of this energy in a laboratory setting before. But at the very highest of energies — energies more than a hundred million (100,000,000) times greater than what we create at the LHC — particles smack into Earth constantly: the great cosmic rays that bombard us from all directions in space. //// These black holes, if they exist, would have been bombarding Earth (and all the planets) for the entire history of our Solar System, as well as the Sun, and there is absolutely no evidence that any body in our Solar System ever became a black hole or got eaten by one. //// But maybe, you’ll object, these objects were moving too quickly, and so they’ll simply pass through the Earth, eating too little matter to remain inside, and pass through to intergalactic space. Well, if that’s your objection, perhaps this second reason-why-this-is-impossible will help you out. //// 2.) If you do create a miniature black hole, they will decay, via Hawking Radiation, on ridiculously small timescales. //// If there are extra dimensions, it is conceivable that they could be of a specific type allowing the (again, very rare, but plausible) formation of a microscopic black hole. This black hole will have, at most, a mass equal to the energy of the proton-proton collision, or up to 13-to-14 TeV. That corresponds, via E=mc^2, to a mass of just 5 x 10^-20 grams, and most likely less. //// But, even if you have extra dimensions of the right scale, and of the right type,and you make this black hole, you still have a problem: it’s unstable. Due to the laws of quantum mechanics, this black hole is going to decay by a process known as . For a black hole of mass 5 x 10^-20 grams, the decay time in three dimensions would be about 10^-83 seconds, which is not even enough time For physics to be meaningful, we need a time of about 10^-43 seconds or longer. Translated into black hole mass, we’d need it to be at least 0.00002 grams to have even a chance of existing. //// In four dimensions, however, especially if the “extra” one is large, the decay time goes all the way up to 10^-23 seconds. Oh, joy. To overcome the expected decay of this miniature black hole, you have to throw out the known laws of physics. These laws are so well-established that it’s inconceivable that they’d be wrong — it would be like waking up tomorrow and seeing the Sun rise in the West. //// But, for argument’s sake, let’s assume there are some new laws of physics that we haven’t conceived of yet that could make these black holes stable. So you make a black hole — a tiny one — at rest with respect to Earth’s center, and it doesn’t decay. Could it eat the Earth? And if so, how fast would that happen? This brings us to our third and final objection, and remember: we’ve already allowed you to throw out the known laws of physics twice to get to this point. //// 3.) You can compute the rate at which a black hole eats matter, and it’s not even close to being as small as the lifetime of our planet. //// We like to think of black holes as “sucking” in matter, but the truth of the matter is, they can only interact with it gravitationally. At a mass of ~5 x 10^-20 grams, that gravitational force it exerts is incredibly weak: all it can manage to do is pass into the Earth’s center and out again, hoping for a collision with an elementary particle as it does so. While the black hole’s cross-section is tiny, the cross-section of a proton (or neutron) is pretty large, and so we can assume — for the sake of argument — that every time the black hole strikes a proton or neutron, it absorbs it. //// Assuming it eats every proton, neutron, or electron that it comes in contact with — and also taking into account its gravity, to see what it attracts — it will eat about 66,000 protons and neutrons per second. Of course, 66,000 protons-and-neutrons is a tiny amount in terms of mass: 1.1 x 10^-25 grams. That rate-of-growth will be constant until the black hole becomes quite large; only at about one billion metric tonnes will the black hole will start to grow faster than this rate, as it takes that long for its cross-section to increase. Capturing 66,000 nucleons per second, how long will it take to get the black hole up to even one kilogram? Three trillion years, which is much longer than the lifetime of the Sun or even the age of the Universe. //// So even if you make a black hole, and even if the laws of physics that we know are wrong and it lives forever, it is still harmless. No matter how many of the laws of physics you throw out, revise or tweak, the Earth will still be okay. //// So take heart! We’re all set to probe the frontiers of physics, to increase our knowledge and understanding of the Universe, and to do it in a totally safe way. Any fears you may have concerning our planet getting eaten by a black hole are completely irrational, and now — armed with the scientific knowledge of why — you can rest easy. //// The world is safe. At least, from physics.

Has Anyone Created a Black Hole on Earth? Credit: Jennifer Lamberth/EyeEm/Getty Images In the popular imagination, black holes are voracious monstrosities gulping down anything in their vicinity. That is why there are occasional worries that physicists might accidentally or intentionally create one, perhaps inside a particle accelerator such as the Large Hadron Collider (LHC) at CERN near Geneva. Would such a dark behemoth swallow up Earth itself? Not quite. No one has ever created a black hole on our planet before. But even if someone did, it likely wouldn’t pose a huge threat. Real-world black holes are only scary in the sense that if you get too close to one, you won’t be able to escape. But even if someone generated a black hole in a laboratory on Earth, the limits of human technology would prevent us from whipping up anything particularly dangerous. “It would likely be so low-mass that its gravitational influence would be relatively small,” says Eliot Quataert, a theoretical astrophysicist at Princeton University. “It wouldn’t actually gobble up that much matter.” In fact, the possibility of creating a black hole in a lab is a goal that scientists are actively pursuing—one that could allow researchers to answer many fundamental questions about quantum mechanics and the nature of gravity. ADVERTISEMENT A black hole typically forms when a star much more massive than our sun dies. While the outer layers of such a star explode outward in a spectacular supernova, its core crumples inward, pressing down toward its central point with so much power that no known force in the universe can stop it. This results in a subatomic spot of unimaginable mass and density whose gravity is so strong that even something traveling at the speed of light couldn’t move fast enough to escape its clutches. These kinds of black holes are common throughout the universe. Of course, as long as something doesn’t get too near a black hole, it’s safe. Only within a spherical boundary surrounding the black hole known as the event horizon would a person or object get pulled inexorably inward. Enormous black holes have a big event horizon—with a diameter of millions of kilometers—whereas smaller ones have more minute event horizons, extending just tens of kilometers across. If you could make a black hole in a lab that weighed only half a kilogram, it would have an event horizon one trillion times smaller than a proton. Fears about the LHC creating a black hole originated with the fact that in Einstein’s special theory of relativity, mass (m) and energy (E) are interchangeable—hence the famous equation E = mc2, where “c” is the speed of light. Because a supercollider slams together protons at unbelievable velocities (nearing the speed of light) and energies, all sorts of strange and exotic particles can pop out, potentially including a black hole. But creating a black hole with even a microscopic event horizon would require billions of times more energy than the LHC is able to produce. And even if it could produce such a black hole, that object would quickly lose energy and dissipate in the blink of an eye. Before the facility turned on in 2008, some researchers had postulated that, if the fabric of spacetime had extra dimensions such as those hypothesized under string theory—a possible way to combine quantum physics and gravity into a single theory—a black hole could appear. That’s because in our four-dimensional universe (with three dimensions of space and one of time), gravity is too weak to pound matter into a black hole. If other dimensions exist, however, gravity may not be the weakling it seems to us, because some of its force could be leaking into these other strange dimensions. In such a universe, a black hole appearing inside an atom smasher becomes much more feasible, potentially revealing insights into the very nature of gravity. This discovery would have been “among the most weird and surprising physics you could see in the LHC,” says Juan Maldacena, a theoretical physicist at the Institute for Advanced Study in Princeton, N.J. ADVERTISEMENT The idea was picked up by the media, producing a large splash. A German chemist even filed a lawsuit against CERN in the European Court of Human Rights. A special committee of physicists had already started looking into the matter in 2003, concluding that because particles from space crash into the atmosphere with energies far greater than those at the supercollider without producing black holes, the possibility appeared to be remote. The committee’s report was reviewed and reissued in 2008 with more information to calm public fears. To date, no black holes have been seen at the LHC. Confirming the predictions of string theory “would have been nice,” Maldacena says, “but it’s not what happened.” More recently, a team announced that it had formed a simulation of a baby wormhole—a type of bridge through reality created from two black holes—using a quantum computer. Though the result was covered widely in the press, it wasn’t exactly the breakthrough that many imagined. newsletter promo Sign up for Scientific American’s free newsletters. Sign Up “What has been created is more like some weird quantum mechanical property of matter that has mathematical properties related to wormholes,” Quataert says. “It’s more of a conceptual connection than a literal connection.” Nevertheless, the research is promising, Maldacena says, and more powerful quantum computers in the future could someday generate objects that simulate black holes using Albert Einstein’s equations, allowing physicists to study their behavior in detail.

--timescale is super distant – 10^8 years – making prediction impossible and making it tactically useless

--indicts Torres