Thought Experiments / Unification


Are Space and Time Fundamental?

Imagine describing our universe to an alien from an alternate dimension. Where would you start?

You might reasonably begin by explaining that we live in three dimensions of space and one dimension of time. Space and time are so fundamental to our understanding of the universe that they are woven into nearly every equation in physics. They are the words in which we speak the language of nature—so tried, tested, and true that we don’t even know how to talk about the cosmos without engaging space and time in the conversation.

But what if it turns out that space and time are not the fundamental infrastructure of our cosmos—what if they are themselves products of some deeper physics?

This idea is called emergence. We see it in nature, as when fish school or birds flock. If you were only to study an individual fish or bird, you would never predict how they would come together as a group. Yet each one “knows” simple rules that, when combined, create a wide range of agile and elegant behaviors. Could it be that physicists have been studying flocks all along, not realizing that it’s the birds that are truly fundamental?

“There aren’t many things in quantum gravity that everyone agrees on,” says Eleanor Knox, a philosopher at King’s College London who specializes in the philosophy of physics. “Yet the one thing many people seemed to agree on in quantum gravity was that we were going to have to cope with space and time not being fundamental.”

It sounds radical, but physics has a long and proud history of spearheading exactly this kind of coup. “Historically, whenever we thought something was fundamental, it turns out that it is not,” says Nathan Seiberg, a theoretical physicist at the Institute for Advanced Study. Kepler, for instance, believed that the Platonic solids were the fundamental constituents of the universe. Today we know better. In the 17th century, scientists thought that cold was a substance that could flow from one place to another, chilling your doorstep or tip of your nose. Now we understand that heat and cold are just another way of talking about the statistical properties of a collection of molecules. Of course, that doesn’t mean that it feels any less real when you burn your tongue on your hot cocoa.

So why are physicists picking on space? Relativity delivered the first strike. “In relativity, space and time are not rigid. They are dynamic,” says Seiberg. Building all of physics on such a malleable infrastructure is akin to constructing your house on a foundation of Jello.

More alarmingly to theorists, our ability to measure features in space is intrinsically limited. A ruler can’t measure distances smaller than the width of its painted markings; the resolution of a microscope is constrained by the wavelength of the light in which it makes images; even scanning tunneling microscopes are limited by the physical size of their probe tips.

Can’t we just build a better microscope? “It’s not because we don’t have the budget to build a powerful enough machine,” explains Seiberg. If we somehow tried to make an infinitely small measuring device, that device would become so dense that it would warp the fabric of space. The conclusion: “Space itself is ambiguous,” says Seiberg. Strike two.

Space also took a hit from an unlikely foe: the hologram. We think of holograms as the dazzling, silvery images on postcards and credit cards: two-dimensional objects that project three-dimensional pictures. More generally, though, a hologram is anything—even an equation—that encodes an extra dimension’s worth of information. It turns out that you can write equations that describe our universe perfectly well using different combinations of spatial dimensions, creating mathematical holograms that are indistinguishable from reality. Like a book that can be translated into many disparate languages without losing a syllable of meaning, our universe seems to tell a story that is independent of the words in which we have always chosen to express it.

Finally, physicists have known for some time that their descriptions of space start to break down when they’re applied to the strange-but-true environments inside black holes and close to the time of big bang. In such cases, the familiar equations start popping out infinities—nonsense answers that suggest that the equations are missing some essential machinery. “Something else should kick in,” says Seiberg.

But what is that something else? “I don’t think I have an answer to that,” says Seiberg. Knox also leaves the door open to as-yet-unknown possibilities: “Whatever it is that’s fundamental, it’s not the stuff we have a handle on right now.” Morever, Seiberg adds that though theorists have assembled a strong case that space is emergent, time presents a more difficult problem. “In order to understand emergent time, we need a complete revolution in the way we think about physics.”

Letting go of space and time without ready replacements may seem like a surefire way to plunge into the abyss of abstraction. But it may be only by loosening our grip that we can come to grasp what is truly fundamental.

Go Deeper
Editor’s picks for further reading

Discover Magazine: Newsflash: Space and Time May Not Exist
If time isn’t fundamental, what is it?

FQXi: Breaking the Universe’s Speed Limit
John Donoghue investigates the possibility that the speed of light is not a constant.

FQXi: Melting Spacetime
Joanna Karczemarek investigates how space and time could emerge from deeper physics.

Tell us what you think on Twitter, Facebook, or email.


Kate Becker

    In a parallel universe, Kate Becker is senior researcher for NOVA and NOVA scienceNOW and a blogger for Inside NOVA. In this universe, she is your host here at The Nature of Reality, and it is her mission to blow your mind with physics. Kate studied physics at Oberlin College and astronomy at Cornell University. You can also follow her on Twitter and Facebook.

    • Mary

      It seems like we tend to put blinders on when we encounter things we know that we can’t prove, things in the flock that we can’t account for in the bird. So maybe we are too equation driven, too inductive. Maybe as scientists we need to be better at considering both directions (bird to flock and flock to bird). Also that time is not directional and space is not expansive. Maybe both directions need equal consideration. Also maybe the discontinuities at 0 and infinity appear because we treat them as opposite ends of a spectrum. Can we find solutions to equations that consider them adjacent, that work in both directions, or that don’t require expansion of time and space?

    • Axel Rod

      Who’s to say that instead of the universe expanding, we are shrinking?

      • Cjoc09

        Hubble said it, and I’m pretty sure the expansion of the universe is no longer a question – it’s a law.

        • Mary

          Most things tends to be cyclic so mayve we are just experiencing the expansion part of a cycle. Even now, whether it is expanding or contracting depends on which direction one is facing. I suspect that the past, present, and future coexist and we are not yet aware of the future, although some of us may have a vague sense of it. I believe when we arrive in the future it will explain the past, thereby demonstrating that it was always there.

    • Mary

      Who’s to say expansion and shrinking don’t coexist?

      • Michelle K. Connolly

        Obviously. lol

      • drd4u

        Mary – my beltline? The wallet? If shrinkage isn’t linnear- then why is the universe cubed? ;-)

      • Cjoc09

        Guth proposed that very possibility. check out ‘eternal inflation’.

    • Harkavy

      Check out Karl Pribram, and also David Bohm’s “Wholeness and the Implicate Order.”

      • Mary

        I am reading it. I like it. It sounds like the Glass Bead Game. Maybe that could be played on this site.

      • drd4u

        Linka linka linka dink…hey? ??? Where’s it at? ;-) thanks…

    • Frank Dunn

      One way to visualise how our space and time emerge from something more funduamantal is to assume that energy density cannot be finite and that both must be quantised at the Planck level ( see for example S W Israel letter to Nature 1991). It is then possible to build ‘complexity models’ of these quanta as Collisional Automata … Like Cellular Automata (see either Wolfram or Conway or others) but they cannot be created or destroyed merely collide. These then stablise into vibrating lattices with ‘synchronised collisions’. these lattices naturally exhibit space-time curvature. Rest mass is then seen as a property of closed loops of these quanta … And other physical properties emerge from there. I offered such models for pubication in the early 90′sbut was unsuccessful.

      • Frank Dunn

        I hit the post button too soon … It should read”energy density cannot be INfinite’

        • drd4u

          Frank – hate to break it to you like this babe…but it is.

          • Mary

            It is ashame that with all your designations after your name you have not learned humility.

            • drd4u

              Mary – sorry you feel like that, truly –

          • Eatonart

            Nothing is infinite except the human capacity for foolishness.

    • Cleantowels

      “Something else should kick in,” says Seiberg.

      But what is that something else? “I don’t think I have an answer to that,” says Seiberg.

      It’s God.

      • Derf

        Or the tooth fairy, Tomato, Tamato.

      • Elbeekanob

        God rolls the dice and any one of many probabilities are possible. We do not live in a ‘clockwork’ universe where everything is dependent on a blueprint.

        • Mary

          Maybe we roll the dice (free will) and God determines the outcome. Or maybe it is some other random event generator. I like things as they are; if we knew it all it would be boring.

        • Trappinglight

          Everything IS dependant on blueprint. If not, you would wake up to a new unfamiliar chaos everyday… “Red light means go today”

      • Michelevanhaecke

        Myself, I think it’s that one guy Fred who comes in every other Wednesday from the temp agency…

      • drd4u

        OK let’s have some fun with that one – Cleantowels – suppose you are right- then why doesn’t it kick in? Before you take the simply obvious overarching “well God is God..etc. ad infinitum ad nauseum-” lets think together- could it possibly be anything else?

        • Cleantowels

          If it is, God made it or did it.

      • gdkzen

        There are two fundamental laws in our universe, which govern everything else: Logic and Probability.

        Everything else is a result of these two laws interacting with each other. Simply because we do not comprehend the logic does not mean exists. By the same token, the nature of probability provides a framework where outcomes may be somewhat, but not completely predictable.

        • gdkzen

          ‘does not mean exists’
          should read
          ‘does not mean that it doesn’t exist’

    • Pazz1972

      The reason our physics breaks down in black holes and at the quantum level is simply because the physics is wrong. As far as the birds flocking together they are doing studies on how animals may be able to share thoughts. The new science of tommorrow isnt coming from well funded scientists in government labs, Its coming from the individuals that dont share its dogma.

      • Michelle K. Connolly


      • drd4u

        Pazz1972 I was with ya ’til you went …dogma…then it all went into the black hole. It’ll come out some day when the Patriot Act says it’s ok to play again…meanwhile- why does light hover in a constant path and yet slightly degrade at the threshold of the black hole?

      • Cfo

        It’s not that the physics is wrong, it’s just incomplete and real scientists have always admitted such. It’s the people who think everything has to be either right or wrong that wind up caving in to models like Creationism and fail to see the value in tring to solve the mysteries of creation.

    • Jwwestvirginia2000

      think of our universe sitting on a lab shelf ! Labeled ” space / time ! What would the beaker next to ours be labeled ? We might just get dumped ! down the drain we go !

    • Stefan Wahe

      It’s simply 42.

    • Michelle K. Connolly

      Time and space are illusions.

      • Carlos Brens

        Michelle: According to Paul Davies’ 7 points summarizing the Anthropic Principle, the seventh “The Fake Universe” states: “We are living in a virtual reality simulation.” You are not far off a viable possibility.

    • Chemstrategy

      Is time really one dimensional? I think of time in three dimensions – past, present, and future ( and they do co-exist). We do know two of three – the third one is known only to our Creator. Yet, we have ability to influence the third dimension of time – no? If so, we can predict its possible outcome

      • drd4u

        Influence – the future – from the present – I take it that’s what you mean? So are you saying there are infinite pasts?

        • Michael Armstrong

          Infinite pasts _and_ infinite futures.

    • drd4u

      Let’s start with the easiest presumption of all- our human vision device, otherwise commonly misnamed as, eye. “What the eye sees, and the ears hear, the mind believes.” -John Travolta “Swordfish” – EXCEPT- as you being a physicist know- we’re seeing something that in reality isn’t there- nothing is solid, is it?

      • Mary

        I learned that we are seeing the Fourier transform of what is there. That was interesting! and we tested it in the optics lab

        • drd4u

          Makes the lad seriously thirsty for a link? Ah…but for a refreshing link in the hot desert of knowledge…;-) Nah, thanks Mary that’s intense…so we’re actually in the midst of a moving transformation on a constant basis?

          • Mary

            To clarify – what we recognize are the coherent points in the wavefront. At all other distances from the object that do not place us at coherent points, our retina performs a Fourier transform so that the object still appears coherent to us. The physics does not match our perception. Windows or mirrors? Windows or Filters?

    • Elbeekanob

      I believe the search for what is fundamental is futile because there is no one thing that can be considered as being fundamental. The Universe is chaotic and random and cannot be understood with our limited minds. Therefore, reality is whatever we perceive it to be. Go beyond the ‘consensual reality’ are create your own. Magic workers have been doing it for thousands of years yet only in this age have we had the ability to measure it.

    • Greg Smith

      If so, what becomes of procrastination?

    • LatashaS

      Lord, let yr glory be revealed!

    • AMJRXX

      All things that have ever happened and shall ever happen are happening right now, this moment, instant, nano-second…now is all, all is now, all is nothing…nothingness is all…

    • Ljtowle

      Yes, Space and Time are indeed fundamental. Since reality can only be perceived and not fully understood scientifically, space and time are the key instruments through which our shared reality is interpreted. These interpretations are approximate at best. How do you put a value on what is perceived? To the painter a flock of birds is a thing of beauty to replicate on a canvas. To the Hunter it is either a food source or game of sport. Which is right? They both are right!

      So if we consider an alternate reality or different world we must consider how that world is perceived by the lifeforms that inhabit that place. What are the origins of their perceptions and how they interpret their reality?

      • gdkzen

        Alas, only a tiny fraction of reality can be sensed. The human mind then uses that sensory input to create a perception of reality.

      • Carlos Brens

        With all due respect, is our present perception of Space and Time fundamental in the same way the luminiferous ether was “fundamental” a while back? I don’t want to hold on too tightly to such notions about space and time for reason of that ether. I’m reluctant to grab on too tightly to dark matter and energy by reason of the work Julian Barbour is doing. Since reality amounts to “perception”, how does that make anything fundamental?

    • Richard Shoupe

      The line between science and mysticism seems to be blurring more and more. It is fascinating (and somewhat amusing) to follow the physicists search for absolutes in a seemingly fluid system of reality. Every question answered suggests a hundred more questions. When will it end? Will it end.

    • Anne Patterson

      its alot to digest but in its self seems to be real

    • Anne Patterson

      its a lot to digest but t the thought has wings

    • God

      Dear nerds,

      I will tell you everything when (and if) you enter my kingdom.

    • Eatonart

      Wow. Aside from the overlooked problem that would be the first order of business, trying to find a way to communicate with these extremely alien beings, and the overlooked fact that if they had found a way to enter our “dimension” then they must know a few things about it already, there is a simpler (but not necessarily the best) resolution to the fundamentality of space and time. Emmanuel Kant posited that space and time were categories imposed by the structure of our minds, governing the ways that we perceive and conceive of everything (except pure mathematical constructs). Of course, if you agree with Hume that our minds are initially tabula rasa, blank slates, and all thoughts and ideas are built from pure sense experience, then you can dismiss Kant, as the modern philosopher Mortimer Adler does. Then you are once again mired in the swamp of such speculations of modern physics as quantum gravity, 11-dimensional spacetime, and the supposed variability of relativistic space and time which was of course resolved in purely geometric terms by Minkowski, a contemporary of Einstein (how soon we forget). Just because a physical theory is mathematically consistent does not mean that it is true; it must be put to some experimental test which is capable of at least falsifying if not necessarily proving it true. Nevertheless, this “thought experiment” involving aliens from another dimension (?) is thought-provoking.

    • Carlos Brens

      But, THERE IS NO SUCH THING AS TIME! A few years ago, I read Julian Barbour’s book “The End of Time” where he actually presents some mathematics that can explain physical properties of the universe without using Einsteinian time as a reference at all. Then I ran into the March issue of Discover, referencing Barbour and his more recent model that aims to do away with Einstein’s 4-dimentional model of Space-Time, completely eliminating time as point of reference (as Mach proposed). Not only does it stand to resolve the problems between the quantum and cosmic, paving the way for a unifying TOE, but it also can actually do away with Dark Matter and Dark Energy all-together. I don’t know a damn thing about, but it sure sounds good.

      • Eatonart

        I’m going to have to go read Mach on that, but anything that can get rid of dark energy and matter would be welcome – they’re a pain in my cosmological butt! I’m just curious what Mach thinks of Minkowski space, where all space-time lengths are invariable with respect to the observer’s velocity. I hope when I read him I’ll find out.

    • Yatin Dhareshwar

      Super article! Very, very well written.

      Though we do not have the answers yet, you have framed the questions eloquently and as a reader, i feel compelled to find the answers right away. But i guess that will have to wait…

      I have been an armchair proponent of emergence being the cause of the birth of the Universe. My theory is that the Universe was created as a result of and emergence of self-organizing dark matter. So yes, emergence does somehow have a role as yet unexplained.

      Interested reader may visit this link for details:

    • Zemandesigns

      Mind blowing…had a vivid dream years ago where there was no time or space and it was like having a dream where the phone rings and it is… times ten.

    • Cfo

      It’s hard enough to try to describe my universe to the next human being. I think my cat has a better handle on relativity than my mother does…And, I’m certain that any such alien would be just as interested in our universe as we are of the philosophical viewpoint of an ant.

    • Cfo

      Whatever other fundamental properties of the universe may exist, I believe that one of the most overlooked, yet significant one is emotion. Emotion being a dynamic force influencing how we percieve reality.

    • Pbarnes

      That’s kind of how I picture God, the great wastewater operator in the sky. He comes in in the morning, takes a sample from the aeration tank, pours it into the settleometer and looks at what he has. If he has too many bacteria or they are not settling good, he may decide to waste some and then we have pestulence, war and famine.

      • Pbarnes

        this was in response to jwwestvirginia2000.

    • Pbarnes

      It seems to me that time is the easy one and that it is clearly emergent. If you think about time and how HUMANS PERCEIVE IT you will see that it depends on physical change. If everything was frozen in place and form (every particle and photon) then we would not have any perception of time. We interpret change (not just any change, but orderly sequential change such as occurs with cause and effect) as time. As we experience it time is more like a property of the other things in the universe than a dimension. The problem with this view is why aren’t all the changes piled on top of each other in the same place? It seems to me that what we experience as time is the interaction of some underlying property “time” of some sort and the rest of our universe, thereby maaking time as we perceive it emergent.

    • Carlos S Gonzales

      Has anyone ever launched 2 telescopes in two opposite directions away from earth? I’m sure having a wider view would unfold untold secrets.

    • Delroy Baugh

      if we ever we become conscious of the other dimension it will give us such a completely and dramatically different view of our reality and, I suspect, our physics as well

    • Comlink33

      i guess i’ll take the Kantian view and just say that space and time are mental faculties, albeit ones in deep use by the physicists conducting these experiments. actually, i’ll go one step further and say theyre just linguistic constructs. im willing to bet that if your first language didnt involve the terms ‘space’ or ‘time’, you wouldnt necessarily have the answers to the problems, but a much different view on them.

    • Tanbotto

      Compatibly with the requirememt that any truly scientific hypothesis needs to be testable or disprovable, this makes for a very interesting topic !

    • Diana Del2512

      Maybe if we could perceive space and time as a human function. Not something that exist beyond us. We created the name space and time in order to understand our reality within this human form. Does energy live by our time and perception of space? We as the observer think so, but that is only our perception within the concept of our understanding. We truly have a lot to learn in understanding that we can assume that things are this way or that way, but it’s those who realize that we are still children learning from a human perceptive. Diana

    • Jcburrritt

      When in college, I asked a math professor, “WHAT IS AT THE OUTER EDGE OF THE UNIVERSE, – A LITTLE WHITE FENCE? (jokingly) His answer was, “THERE IS NO SUCH THING AS A STRAIGHT LINE.” I have since realized that the light that we see from a star comes at us at the speed of light (186,000 miles per second), and the star may have already burned up into a black hole, but that light is still coming toward us.

    • So Close to interesting

      ( I’ll put the mea culpa up front. ) It would be of immense intellectual satisfaction and import to understand these things, and I admire Eleanor Knox’s dedication to that quest. But I humbly request that we put the same amount of time and effort into solving the mysteries of human courage and compassion. Words have their place, but our times really call for deeds.

    • rodneyb

      I have been watching Nova “The Fabric of the Cosmos”. Nova is such a great show. Things That I didn’t think I would ever be able to understand, come to life. I do have a question about gravity as it was explained in the show. I hope I am in a place to get the answer or that someone can point me in the right direction. Spacetime is a fabric that holds our moon in place and we call that gravity and that makes since. However how does that same fabric idea keep my feet on the ground? Am I being pushed into the earth instead of pulled?

    • Anonymous

      The holographic nature of reality is real clue, in my opinion. We don’t exist in what we think we do. But a question arises…what can the hologram know about the projector? We may be trapped in a reality where its true nature is beyond our reach.

    • Anonymous

      The Universe & Our Place in its midst: Finally we can take the decision that our lifetime Universe is Digital found a- Multimedia DEMO “Brief History of the Universe”

    • lenni

      Sorry to back to the start but I have found a new definition of time. It is very interesting and absolutely new. Even more, the professor (who wrote the theory) claims, thought’s time. It must be something in it, since there will be a thought power contest, based on this theory. A contest where you move real things with thoughts. In this case I would like to learn about this theory. Do you know it?

    • Renis

      In more general terms, it is possible to make a
      comparison as to how there should be a connection between what stars look like
      and the replication of a star-like formation in cells and consider black or
      white holes as a possible influence of forces acting in sub-atomic level by
      allowing a theoretical model that is complete and detailed in matching the high number of dimensions used in quantum physics with all comparisons in terms of information much like the event horizon of black holes.

    • zankaon

      The Hubble expansion I.e. expansion of universe, can utilized as indicative of a common cosmic time. See