究竟什么是物质?

究竟什么是物质,哲学上又指什么?

原道童子 作答:

物质的定义是极其困难的,目前尚无精准的物质定义。定义是科学研究的灵魂,有了精准的定义,其它一切问题皆迎刃而解。

以下是我对物质的探讨。我的思路是:物质的语义学定义→物质的唯物论定义→物质的物理学定义。显然,物质的物理学定义是关键。

一,物质的语义学定义。

汉语的物质是联合词组。物,即物像,是感觉的外在形象,是形式或外延。质,是直觉的内在结构,是内容或内涵。因此,物质的意思可引申为:①形式与内容的统一体,②外延与内涵的统一体,③结构与功能的统一体,④存在与意识的统一体。

英语的物质有两个词。一是matter,本意是麻烦,说不清道不明。二是substance,源于拉丁语汇。sub是under,意思是低下而潜在的。stance是站立的姿态,引申为形式。由此可见,物质是一种非意识的存在形式。

二,物质的马哲学定义。

马哲物质论这样陈述:物质是不依赖人们意志但可被人的意识所反映的客观实在。世界是物质的,物质是运动的。运动是物质的存在方式,物质世界是可以被认知的。

我理解,马哲物质论:①物质是无处不在的,进而真空也是物质的;②物质是有形的,进而是有质量的;③物质是运动的,进而是有能量的;④物质是可知的,进而是可测量的。

我认为,马哲物质论:具有高度的逻辑性与科学性,可以指导自然科学研究,可以作为识别伪科学的判断依据,也可知道物理学对物质做出精准的科学定义。

我请问:狭义相对论分出静质量与动质量,意味着物质有静止态,这个命题可信么?广义相对论的引力场方程,否定宇宙真空场,意味着真空的物质性不存在,这个方程可信么?

三,物质的物理学定义。

迄今为止,我们从未见识物理学对物质有一个明明白白的精准定义,导致恣意数学的非物质学说,这不能不说是物理学的一个瑕疵。

我们批判与反思现有物理学的乱象,目的是要建立一套足以逻辑自洽的深度解读物质的物理新思维。

相对论与量子论各执一词,各有弊端。相对论的致命瑕疵是否定漩涡真空场,而仅凭卡什米尔效应(Casimir Effect),就足以证否相对论。

量子论的纠缠超距说,用臆断的波函数塌陷搪塞,仅凭其以否定因果律为代价,就足以证伪量子纠缠理论,薛定谔的猫论可以休矣。

我认为,物质的物理学定义,可以这么定义:物质是①在绝对时空参照系下②基于真空漩涡场的③既有自旋又有绕旋之谐振子的④或独立自由或叠加约束的⑤既有质量又有能量的⑥或直接测量或间接测量的⑦客观存在形式。

我以为,这个定义复杂而严谨,可称物质的七要素定义,以下分别说明七要素的理由。

①物质的认知必须以绝对时空作为参照系。

旨在奠基一个最为简洁的测量基准与零点坐标。经典动力学体系的物理公理集,创造了人类有史以来极其辉煌的物质技术装备成就,这得归功于笛卡尔直角坐标系,即三维空间参照系。

可以理解:空间的无限延伸性与绝对静止性,参照系的任意可选择性,最符合人择原理。

狭义相对论搞了一个移动空间参照系,广义相对论搞了一个弯曲时空参照系,纯属多此一举。宇宙大爆炸广受诟病,就是把无限延伸的宇宙,看成一个弯曲膨胀的球。

②物质是基于真空漩涡场的(色空亦空)。

无数事实,尤其是真空吸尘器与Casimir效应证明,真空是一个最为普遍的客观实在。因为气流旋转龙卷风有了真空漩涡场。因为凸面绕旋,机翼上方有了真空漩涡场。因为涵洞漩涡,有了垂直下凹的真空场。因为离心泵旋转,泵腔有了真空漩涡场。

③物质来自既有自旋又有绕旋的基本粒子。

电子以光速自旋,同时有了电子的真空漩涡场,有了电偶极子、电子磁矩、电子电荷、电子质量、电子自旋角动量、电子势能、电子引力场、电子半径(2.82e-15m)、电子椭球体、电子进动、电子绕旋、电子的自我存在形式。

质子以光速自旋,同时有了质子的真空漩涡场,有了电偶极子、质子电荷、质子质量、质子自旋角动量、质子势能、质子引力场、质子半径(2.21e-16m),质子进动、质子椭球体、质子震荡、质子的自我存在形式。

④物质是或独立自由或叠加约束的。

费米子,诸如中微子、电子、质子、中子,都是一种自旋与绕旋的统一体,因自旋产生转动惯量不均衡的椭球体。同时因惯量不均衡产生进动或绕旋的椭圆轨道。

玻色子,诸如引力子、光子、胶子,都是能密不同的真空漩涡场的场量子。引力子是是一个真空涟漪,是质密与能密最小的物质单元。

光子是数亿引力子环环相扣的簇合体,光子的自旋半径:R=λ/2π。原子核内空间的胶子或介子,是高能密的玻色子,也是环环相扣的数亿引力子的簇合体。

⑤物质是既有质量又有能量的。

质量与能量是物质不可分割的内在属性。所有费米子与玻色子的质密参数与能密参数,皆以绝对时空为参照系。核子的光速自旋,对应自旋势能。例如,质子的内秉质量m=1.73e-27kg,对应质子自旋势能Ep=mc²=938MeV。

如果不是粉碎了电子或质子的存在形式,即如果不是粉碎了电子或质子的自旋势能,那么能量守恒的本质就是动能守恒,质量守恒的本质是电子与质子永远保持内秉的自旋势能。

通常情况下,即便粉碎了中子,中子也只是主要衰变为质子与电子。正负电子湮灭变成正负光子,但光子依然有物理新思维下质量与能量,只是电子的自旋势能变成了光子的自旋势能。为简便起见,不妨说一个基态光子的质量,等同于一个基态电子的质量。

⑥或直接测量或间接测量。

毫无疑问,任何物理学说的物理参量,必须以获得测量数值为依据,否则就是胡说八道。例如,宇宙大爆炸达到的普朗克温度,没有测量依据,纯属臆断。黑洞的质密能密参数,没有测量依据,纯属胡扯。

然而,本文特别重视的真空漩涡场,是可以通过测量与逻辑类比,间接测量与直接推理的。

⑦物质是客观存在形式,而非数学臆断。

有一种流行的谬论说:宇宙那么大有无限的变数,只要有数学推演的结果,就一定在宇宙中存在,尤其毕达哥拉斯断言,宇宙的本质就是数。这些脱离物理测量与客观实际,纯凭数学臆造,是极为有害的数学唯心主义。

最典型的莫过狄拉克基于数学轴对称的反物质猜想。事实上,自然界不存在绝对对称的玩意。一切都是不均衡的:没有相同的两个基因,没有相同的地球绕日轨道,没有相同的电子绕核轨道。量子论中的全同粒子,只是忽略了次要因素的近似手段,而已。

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龚学理论评注:

龚学可以用一个方程表示空间、物质、时间:

DS =(i^n1,i^n2,i^n3)* C * DT =N * C * DT……(方程0)

i是虚数,i^n1是i 的n1幂次,同样i^ n2和i^n3;

{n1, n2, n3}自然数取值范围(0,1,2,3)或(1,2,3,4);

DS是一个空间单元,DT一个时间单元;C是光速。

N是一个虚-实数域,而N方有四个可能的值。

N^ 2 = { + / – 1 ,+ / – 3 } ………….(方程0’)

方程0以精确的方式连接时间、空间和物质。虚-实数域的N产生64个子空间。“方程0’  ”是一个选择规则。当一个子空间有N ^2 = + / – 3,那么这个子空间是一个真正的实空间,相当于广义相对论的3维纯真空实空间(X,Y,Z),与3维虚空间(iX, i Y, i Z)。当N ^2= + / – 1,这是一个子空间,事实上,是一个基本粒子。方程0包含48个这样的子空间,因此,给出48个基本粒子(费米子物质)。

物质就是由时间驱动光子在真实三维和虚三维空间光速旋转的子空间,包括可见物质和暗物质。

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INNOVATIONS IN

doi: 10.1038/d41586-018-05096-y

This article is part of Innovations In The Biggest Questions In Science, an editorially independent supplement produced with the financial support of third parties. About this content.

What Is Dark Matter?

An elusive substance that permeates the universe exerts many detectable gravitational influences yet eludes direct detection.

Illustration by Chris Gash

Physicists and astronomers have determined that most of the material in the universe is “dark matter”—whose existence we infer from its gravitational effects but not through electromagnetic influences such as we find with ordinary, familiar matter. One of the simplest concepts in physics, dark matter can nonetheless be mystifying because of our human perspective. Each of us has five senses, all of which originate in electromagnetic interactions. Vision, for example, is based on our sensitivity to light: electromagnetic waves that lie within a specific range of frequencies. We can see the matter with which we are familiar because the atoms that make it up emit or absorb light. The electric charges carried by the electrons and protons in atoms are the reason we can see.

Matter is not necessarily composed of atoms, however. Most of it can be made of something entirely distinct. Matter is any material that interacts with gravity as normal matter does—becoming clumped into galaxies and galaxy clusters, for example.

There is no reason that matter must always consist of charged particles. But matter that has no electromagnetic interactions will be invisible to our eyes. So-called dark matter carries no (or as yet undetectably little) electromagnetic charge. No one has seen it directly with his or her eyes or even with sensitive optical instruments. Yet we believe it is out there because of its manifold gravitational influences. These include dark matter’s impact on the stars in our galaxy (which revolve at speeds too great for ordinary matter’s gravitational force to rein in) and the motions of galaxies in galaxy clusters (again, too fast to be accounted for only by matter that we see); its imprint on the cosmic microwave background radiation left over from the time of the big bang; its influence on the trajectories of visible matter from supernova expansions; the bending of light known as gravitational lensing; and the observation that the visible and invisible matter gets separated in merged galaxy clusters.

Perhaps the most significant sign of the existence of dark matter, however, is our very existence. Despite its invisibility, dark matter has been critical to the evolution of our universe and to the emergence of stars, planets and even life. That is because dark matter carries five times the mass of ordinary matter and, furthermore, does not directly interact with light. Both these properties were critical to the creation of structures such as galaxies—within the (relatively short) time span we know to be a typical galaxy lifetime—and, in particular, to the formation of a galaxy the size of the Milky Way. Without dark matter, radiation would have prevented clumping of the galactic structure for too long, in essence wiping it out and keeping the universe smooth and homogeneous. The galaxy essential to our solar system and our life was formed in the time since the big bang only because of the existence of dark matter.

Some people, on first hearing about dark matter, feel dismayed. How can something we do not see exist? At least since the Copernican revolution, humans should be prepared to admit their noncentrality to the makeup of the universe. Yet each time people learn about it in a new context, many get confused or surprised. There is no reason that the matter we see should be the only type of matter there is. The existence of dark matter might be expected and is compatible with everything we know.

Perhaps some confusion lies in the name. Dark matter should really be called transparent matter because, as with all transparent things, light just passes through it. Nevertheless, its nature is far from transparent. Physicists and astronomers would like to understand, at a more fundamental level, what exactly dark matter is. Is it made up of a new type of fundamental particle, or does it consist of some invisible, compact object, such as a black hole? If it is a particle, does it have any (albeit very weak) interaction with familiar matter, aside from gravity? Does that particle have any interactions with itself that would be invisible to our senses? Is there more than one type of such a particle? Do any of these particles have interactions of any sort?

My theoretical colleagues and I have thought about a number of interesting possibilities. Ultimately, however, we will learn about the true nature of dark matter only with the help of further observations to guide us. Those observations might consist of more detailed measurements of dark matter’s gravitational influence. Or—if we are very lucky and dark matter does have some tiny, nongravitational interaction with ordinary matter we have so far failed to observe—big underground detectors, satellites in space or the Large Hadron Collider at CERN near Geneva might in the future detect dark matter particles. Even without such interactions with ordinary matter, dark matter’s self-interactions might have observable consequences. For example, the internal structure of galaxies at small scales will be different if dark matter’s interactions with itself rearrange matter at galactic centers. Compact or other structures akin to the Milky Way, such as the bright gas clouds and stars we see when we look at the night sky, could indicate one or more distinct species of dark matter particles that interact with one another. Or hypothesized particles called axions that interact with magnetic fields might be detected in laboratories or in space.

For a theorist, an observer or an experimentalist, dark matter is a promising target for research. We know it exists, but we do not yet know what it is at a fundamental level. The reason we do not know might be obvious by now: it is just not interacting enough to tell us, at least so far. As humans, we can only do so much if ordinary matter is essentially oblivious to anything but dark matter’s very existence. But if dark matter has some more interesting properties, researchers are poised to find them—and, in the process, to help us more completely address this wonderful mystery.

Nature 557, S6-S7 (2018)

doi: 10.1038/d41586-018-05096-y

This article is part of Innovations In The Biggest Questions In Science, an editorially independent supplement produced with the financial support of third parties. About this content.

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INNOVATIONS IN

What Is Spacetime?

Physicists believe that at the tiniest scales, space emerges from quanta. What might these building blocks look like?

Illustration by Chris Gash

People have always taken space for granted. It is just emptiness, after all—a backdrop to everything else. Time, likewise, simply ticks on incessantly. But if physicists have learned anything from the long slog to unify their theories, it is that space and time form a system of such staggering complexity that it may defy our most ardent efforts to understand.

Albert Einstein saw what was coming as early as November 1916. A year earlier he had formulated his general theory of relativity, which postulates that gravity is not a force that propagates through space but a feature of spacetime itself. When you throw a ball high into the air, it arcs back to the ground because Earth distorts the spacetime around it, so that the paths of the ball and the ground intersect again. In a letter to a friend, Einstein contemplated the challenge of merging general relativity with his other brainchild, the nascent theory of quantum mechanics. That would not merely distort space but dismantle it. Mathematically, he hardly knew where to begin. “How much have I already plagued myself in this way!” he wrote.

Einstein never got very far. Even today there are almost as many contending ideas for a quantum theory of gravity as scientists working on the topic. The disputes obscure an important truth: the competing approaches all say space is derived from something deeper—an idea that breaks with 2,500 years of scientific and philosophical understanding.

Down the Black Hole

A kitchen magnet neatly demonstrates the problem that physicists face. It can grip a paper clip against the gravity of the entire Earth. Gravity is weaker than magnetism or than electric or nuclear forces. Whatever quantum effects it has are weaker still. The only tangible evidence that these processes occur at all is the mottled pattern of matter in the very early universe—thought to be caused, in part, by quantum fluctuations of the gravitational field.

Black holes are the best test case for quantum gravity. “It’s the closest thing we have to experiments,” says Ted Jacobson of the University of Maryland, College Park. He and other theorists study black holes as theoretical fulcrums. What happens when you take equations that work perfectly well under laboratory conditions and extrapolate them to the most extreme conceivable situation? Will some subtle flaw manifest itself?

General relativity predicts that matter falling into a black hole becomes compressed without limit as it approaches the center—a mathematical cul-de-sac called a singularity. Theorists cannot extrapolate the trajectory of an object beyond the singularity; its time line ends there. Even to speak of “there” is problematic because the very spacetime that would define the location of the singularity ceases to exist. Researchers hope that quantum theory could focus a microscope on that point and track what becomes of the material that falls in.

Out at the boundary of the hole, matter is not so compressed, gravity is weaker and, by all rights, the known laws of physics should still hold. Thus, it is all the more perplexing that they do not. The black hole is demarcated by an event horizon, a point of no return: matter that falls in cannot get back out. The descent is irreversible. That is a problem because all known laws of fundamental physics, including those of quantum mechanics as generally understood, are reversible. At least in principle, you should be able to reverse the motion of all the particles and recover what you had.

A very similar conundrum confronted physicists in the late 1800s, when they contemplated the mathematics of a “black body,” idealized as a cavity full of electromagnetic radiation. James Clerk Maxwell’s theory of electromagnetism predicted that such an object would absorb all the radiation that impinges on it and that it could never come to equilibrium with surrounding matter. “It would absorb an infinite amount of heat from a reservoir maintained at a fixed temperature,” explains Rafael Sorkin of the Perimeter Institute for Theoretical Physics in Ontario. In thermal terms, it would effectively have a temperature of absolute zero. This conclusion contradicted observations of real-life black bodies (such as an oven). Following up on work by Max Planck, Einstein showed that a black body can reach thermal equilibrium if radiative energy comes in discrete units, or quanta.

Theoretical physicists have been trying for nearly half a century to achieve an equivalent resolution for black holes. The late Stephen Hawking of the University of Cambridge took a huge step in the mid-1970s, when he applied quantum theory to the radiation field around black holes and showed they have a nonzero temperature. As such, they can not only absorb but also emit energy. Although his analysis brought black holes within the fold of thermodynamics, it deepened the problem of irreversibility. The outgoing radiation emerges from just outside the boundary of the hole and carries no information about the interior. It is random heat energy. If you reversed the process and fed the energy back in, the stuff that had fallen in would not pop out; you would just get more heat. And you cannot imagine that the original stuff is still there, merely trapped inside the hole, because as the hole emits radiation, it shrinks and, according to Hawking’s analysis, ultimately disappears.

This problem is called the information paradox because the black hole destroys the information about the infalling particles that would let you rewind their motion. If black hole physics really is reversible, something must carry information back out, and our conception of spacetime may need to change to allow for that.

Atoms of Spacetime

Heat is the random motion of microscopic parts, such as the molecules of a gas. Because black holes can warm up and cool down, it stands to reason that they have parts—or, more generally, a microscopic structure. And because a black hole is just empty space (according to general relativity, infalling matter passes through the horizon but cannot linger), the parts of the black hole must be the parts of space itself. As plain as an expanse of empty space may look, it has enormous latent complexity.

Even theories that set out to preserve a conventional notion of spacetime end up concluding that something lurks behind the featureless facade. For instance, in the late 1970s Steven Weinberg, now at the University of Texas at Austin, sought to describe gravity in much the same way as the other forces of nature. He still found that spacetime is radically modified on its finest scales.

Physicists initially visualized microscopic space as a mosaic of little chunks of space. If you zoomed in to the Planck scale, an almost inconceivably small size of 10–35 meter, they thought you would see something like a chessboard. But that cannot be quite right. For one thing, the grid lines of a chessboard space would privilege some directions over others, creating asymmetries that contradict the special theory of relativity. For example, light of different colors might travel at different speeds—just as in a glass prism, which refracts light into its constituent colors. Whereas effects on small scales are usually hard to see, violations of relativity would actually be fairly obvious.

The thermodynamics of black holes casts further doubt on picturing space as a simple mosaic. By measuring the thermal behavior of any system, you can count its parts, at least in principle. Dump in energy and watch the thermometer. If it shoots up, that energy must be spread out over comparatively few molecules. In effect, you are measuring the entropy of the system, which represents its microscopic complexity.

If you go through this exercise for an ordinary substance, the number of molecules increases with the volume of material. That is as it should be: If you increase the radius of a beach ball by a factor of 10, you will have 1,000 times as many molecules inside it. But if you increase the radius of a black hole by a factor of 10, the inferred number of molecules goes up by only a factor of 100. The number of “molecules” that it is made up of must be proportional not to its volume but to its surface area. The black hole may look three-dimensional, but it behaves as if it were two-dimensional.

This weird effect goes under the name of the holographic principle because it is reminiscent of a hologram, which presents itself to us as a three-dimensional object. On closer examination, however, it turns out to be an image produced by a two-dimensional sheet of film. If the holographic principle counts the microscopic constituents of space and its contents—as physicists widely, though not universally, accept—it must take more to build space than splicing together little pieces of it.

The relation of part to whole is seldom so straightforward, anyway. An H2O molecule is not just a little piece of water. Consider what liquid water does: it flows, forms droplets, carries ripples and waves, and freezes and boils. An individual H2O molecule does none of that: those are collective behaviors. Likewise, the building blocks of space need not be spatial. “The atoms of space are not the smallest portions of space,” says Daniele Oriti of the Max Planck Institute for Gravitational Physics in Potsdam, Germany. “They are the constituents of space. The geometric properties of space are new, collective, approximate properties of a system made of many such atoms.”

What exactly those building blocks are depends on the theory. In loop quantum gravity, they are quanta of volume aggregated by applying quantum principles. In string theory, they are fields akin to those of electromagnetism that live on the surface traced out by a moving strand or loop of energy—the namesake string. In M-theory, which is related to string theory and may underlie it, they are a special type of particle: a membrane shrunk to a point. In causal set theory, they are events related by a web of cause and effect. In the amplituhedron theory and some other approaches, there are no building blocks at all—at least not in any conventional sense.

Although the organizing principles of these theories vary, all strive to uphold some version of the so-called relationalism of 17th- and 18th-century German philosopher Gottfried Leibniz. In broad terms, relationalism holds that space arises from a certain pattern of correlations among objects. In this view, space is a jigsaw puzzle. You start with a big pile of pieces, see how they connect and place them accordingly. If two pieces have similar properties, such as color, they are likely to be nearby; if they differ strongly, you tentatively put them far apart. Physicists commonly express these relations as a network with a certain pattern of connectivity. The relations are dictated by quantum theory or other principles, and the spatial arrangement follows.

Phase transitions are another common theme. If space is assembled, it might be disassembled, too; then its building blocks could organize into something that looks nothing like space. “Just like you have different phases of matter, like ice, water and water vapor, the atoms of space can also reconfigure themselves in different phases,” says Thanu Padmanabhan of the Inter-University Center for Astronomy and Astrophysics in India. In this view, black holes may be places where space melts. Known theories break down, but a more general theory would describe what happens in the new phase. Even when space reaches its end, physics carries on.

Entangled Webs

The big realization of recent years—and one that has crossed old disciplinary boundaries—is that the relevant relations involve quantum entanglement. An extrapowerful type of correlation, intrinsic to quantum mechanics, entanglement seems to be more primitive than space. For instance, an experimentalist might create two particles that fly off in opposing directions. If they are entangled, they remain coordinated no matter how far apart they may be.

Traditionally when people talked about “quantum” gravity, they were referring to quantum discreteness, quantum fluctuations and almost every other quantum effect in the book—but never quantum entanglement. That changed when black holes forced the issue. Over the lifetime of a black hole, entangled particles fall in, but after the hole evaporates fully, their partners on the outside are left entangled with—nothing. “Hawking should have called it the entanglement problem,” says Samir Mathur of Ohio State University.

Even in a vacuum, with no particles around, the electromagnetic and other fields are internally entangled. If you measure a field at two different spots, your readings will jiggle in a random but coordinated way. And if you divide a region in two, the pieces will be correlated, with the degree of correlation depending on the only geometric quantity they have in common: the area of their interface. In 1995 Jacobson argued that entanglement provides a link between the presence of matter and the geometry of spacetime—which is to say, it might explain the law of gravity. “More entanglement implies weaker gravity—that is, stiffer spacetime,” he says.

Several approaches to quantum gravity—most of all, string theory—now see entanglement as crucial. String theory applies the holographic principle not just to black holes but also to the universe at large, providing a recipe for how to create space—or at least some of it. For instance, a two-dimensional space could be threaded by fields that, when structured in the right way, generate an additional dimension of space. The original two-dimensional space would serve as the boundary of a more expansive realm, known as the bulk space. And entanglement is what knits the bulk space into a contiguous whole.

In 2009 Mark Van Raamsdonk of the University of British Columbia gave an elegant argument for this process. Suppose the fields at the boundary are not entangled—they form a pair of uncorrelated systems. They correspond to two separate universes, with no way to travel between them. When the systems become entangled, it is as if a tunnel, or wormhole, opens up between those universes, and a spaceship can go from one to the other. As the degree of entanglement increases, the wormhole shrinks in length, drawing the universes together until you would not even speak of them as two universes anymore. “The emergence of a big spacetime is directly tied into the entangling of these field theory degrees of freedom,” Van Raamsdonk says. When we observe correlations in the electromagnetic and other fields, they are a residue of the entanglement that binds space together.

Many other features of space, besides its contiguity, may also reflect entanglement. Van Raamsdonk and Brian Swingle, now at the University of Maryland, College Park, argue that the ubiquity of entanglement explains the universality of gravity—that it affects all objects and cannot be screened out. As for black holes, Leonard Susskind of Stanford University and Juan Maldacena of the Institute for Advanced Study in Princeton, N.J., suggest that entanglement between a black hole and the radiation it has emitted creates a wormhole—a back-door entrance into the hole. That may help preserve information and ensure that black hole physics is reversible.

Whereas these string theory ideas work only for specific geometries and reconstruct only a single dimension of space, some researchers have sought to explain how all of space can emerge from scratch. For instance, ChunJun Cao, Spyridon Michalakis and Sean M. Carroll, all at the California Institute of Technology, begin with a minimalist quantum description of a system, formulated with no direct reference to spacetime or even to matter. If it has the right pattern of correlations, the system can be cleaved into component parts that can be identified as different regions of spacetime. In this model, the degree of entanglement defines a notion of spatial distance.

In physics and, more generally, in the natural sciences, space and time are the foundation of all theories. Yet we never see spacetime directly. Rather we infer its existence from our everyday experience. We assume that the most economical account of the phenomena we see is some mechanism that operates within spacetime. But the bottom-line lesson of quantum gravity is that not all phenomena neatly fit within spacetime. Physicists will need to find some new foundational structure, and when they do, they will have completed the revolution that began just more than a century ago with Einstein.

Nature 557, S3-S6 (2018)

doi: 10.1038/d41586-018-05095-z

This article is part of Innovations In The Biggest Questions In Science, an editorially independent supplement produced with the financial support of third parties. About this content.

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