Astronomy Without A Telescope – Is Time Real?

by Steve Nerlich on June 12, 2010

Time is an illusion caused by the passage of history (Douglas Adams 1952-2001).

The way that we deal with time is central to a major current schism in physics. Under classic Newtonian physics and also quantum mechanics – time is absolute, a universal metronome allowing you determine whether events occur simultaneously or in sequence. Under Einstein’s physics, time is not absolute – simultaneity and sequence depend on who’s looking. For Einstein, the speed of light (in a vacuum) is constant and time changes in whatever way is required to keep the speed of light constant from all frames of reference.

Under general relativity (GR) you are able to experience living for three score and ten years regardless of where you are or how fast you’re moving, but other folk might measure that duration quite differently. But even under GR, we need to consider whether time only has meaning for sub-light speed consciousnesses such as us. Were a photon to have consciousness, it may not experience time – and, from its perspective, would cross the apparent 100,000 light year diameter of the Milky Way in an instant. Of course, that gets you wondering whether space is real either. Hmm…

Quantum mechanics does (well, sometimes) require absolute time – most obviously in regards to quantum entanglement where determining the spin of one particle, determines the spin of its entangled partner instantaneously and simultaneously. Leaving aside the baffling conundrums imposed by this instantaneous action over a distance – the simultaneous nature of the event implies the existence of absolute time.

In one attempt to reconcile GR and quantum mechanics, time disappears altogether – from the Wheeler-DeWitt equation for quantum gravity – not that many regard this as a 100% successful attempt to reconcile GR and quantum mechanics. Nonetheless, this line of thinking highlights the ‘problem of time’ when trying to develop a Theory of Everything.

The winning entries for a 2008 essay competition on the nature of time run by the Fundamental Questions Institute could be roughly grouped into the themes ‘time is real’, ‘no, it isn’t’ and ‘either way, it’s useful so you can cook dinner.’

The ‘time isn’t real’ camp runs the line that time is just a by-product of what the universe does (anything from the Earth rotating to the transition of a Cesium atom – i.e. the things that we calibrate our clocks to).

How a return to equilibrium after a random downward fluctuation in entropy might appear. First there was light, then a whole bunch of stuff happened and then it started getting cold and dark and empty.

Time is the fire in which we burn (Soran, Star Trek bad guy, circa 24th century).

‘Time isn’t real’ proponents also refer to Boltzmann’s attempt to trivialise the arrow of time by proposing that we just live in a local pocket of the universe where there has been a random downward fluctuation of entropy – so that the perceived forward arrow of time is just a result of the universe returning to equilibrium – being a state of higher entropy where it’s very cold and most of the transient matter that we live our lives upon has evaporated. It is conceivable that another different type of fluctuation somewhere else might just as easily result in the arrow pointing the other way.

Nearly everyone agrees that time probably doesn’t exist outside our Big Bang universe and the people who just want to get on and cook dinner suggest we might concede that space-time could be an emergent property of quantum mechanics. With that settled, we just need to rejig the math – over coffee maybe.

I was prompted to write this after reading a Scientific American June 2010 article, Time Is An Illusion by Craig Callender.

Tagged as: entropy, spacetime, time

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  • http://www.cheapastro.com Steve Nerlich

    @ TL

    I haven’t had time to read Sean Carroll’s book either :-)

    But he did put an essay into the fqxi competition:
    http://www.fqxi.org/data/essay-contest-files/Carroll_fqxitimecontest.pdf
    - and there he suggested we could concede space-time as an emergent property of quantum mechanics. Frankly, I’m not completely sure what that means – but it sounds cool.

    With your card players analogy – the words ‘as soon as…’ surely imply simultaneity?

  • Olaf

    @Duncan Ivry,

    Why should a Scientists feel consequences on personal life if time is real or not? It is not confirmed to be real and it is not confirmed to be not real, so why would it have any effect on their personal lives?

    Also if time is not real, it would have no difference in your lifetime at macroscopic level. You are still bound through these physical rules you cannot escape from.

  • Olaf

    I am just wondering, if a photon not experience time but a photo travels from one part of the universe to another through e predefined rout in space-time. And it is constant no matter how fast you move and no matter what direction.

    Could this be some dimensional ripple of spacetime a bit like a string in spacetime? (No I don;t understand the mathenatics…. yet) I was thinking about a shore wave and suddenly I wondered if a photon looked like a shore wave but in an additional dimension.

  • Lawrence B. Crowell

    @ Olaf, the no time property of the photon is easily seen with special relativity. The proper time of a photon is zero. However, for an observer on a frame the photon moves between two points at the speed of light in a time t = d/c, d = distance between the points.

    I tried to illustrate some aspect of how spacetime physics may emerge from quantum physics. This involves the correspondence beteen anti de Sitter spacetime and a conformal field theory. The same basic idea applied to black holes is the holography principle. The AdS-CFT is the holography principle applied to the boundary of the AdS. This is rather advanced physics and not easy to write up in a short blog post.

    LC

  • Olaf

    I agree LBS, it is way beyond my current understanding this topic. But also very interesting.

  • Richard Kirk

    I am not sure there is really an argument here. Or, rather, if there is an argument, it lies in the definition of the words used to express the ideas.

    Here’s a simple example. You have a Young’s slits experiment. You dim the light source so only one photon is going to be passing through the slits at a time, but you still get fringes. So, we have a wave of ‘probablility’ that goes through both slits, but the entire particle will arrive at one place on the other side. The first time we meet this, we feel bound to ask “but what’s it _really_ doing?”.

    Really doing? We have some equations that predict how it will behave. If the equations are correct, then this is what it will do, or will do on average for quantum processes. If there is a reality, then the equations are describing it. This description doesn’t seem to make sense when we are only used to macroscopic objects.

    The first people reading Newton were unhappy with the idea of bodies moving without friction. If you find quantum mechanics weird and strange, well it probably seemed that way to all of us once. I don’t thisk I have ever ‘understood’ QM or anything else – it has just become familiar. I learned that all sorts of particles have wavefunctions, but ‘real’ macroscopic objects are unlikely to have an observable wavefunction, which is why I don’t see them. I learn what the equations can do. In the end, the mental rigidity that is ‘common sense’ yields a bit, and there is room in the head for a new idea.

    Okay – back to the major topic. Is time real? I’ll answer that one when you have explained what ‘real’ is. But, whether it is ‘real’ or not, I will still use equations with d/dt in.

  • Duncan Ivry

    Olaf: “Why should a Scientists feel consequences on personal life if time is real or not?”

    As I said, I’m not completely serious. But: If time is *what*, please?

    Olaf: “It is not confirmed to be real and it is not confirmed to be not real, so why would it have any effect on their personal lives?”

    I’m not quite with you. Time being “real” versus “not real” doesn’t have any state of confirmation or non-confirmation, it is *not* *defined*.

    Olaf: “Also if time is not real, it would have no difference in your lifetime at macroscopic level. You are still bound through these physical rules you cannot escape from.”

    Starting with time having this completely undefined property you make a conclusion? Well, I think, time is … er … say, “ytrewq” or not “ytrewq”. Because the term “ytrewq” is not defined, the statement “time is (not) ytrewq” makes no sense. You get the point?

    Most, if not all, entries for the 2008 essay competition on the nature of time are not science but science fiction. As I have said before, I like science fiction very much. For me it’s okay talking about science fiction here at Universe Today. But from a scientific point of view most science fiction is impossible or even nonsense — which doesn’t matter ;-)

  • Leo

    Forgive me if I am asking a stupid question, but I remember reading an article saying that gps sattelites had to be calibrated to include the effects of gravity on time. (This is WAY above my understanding, but still awesome.) If gravity can effect time, doesn’t that prove that time exists in a physical sense? Then again, I might be totally wrong….

  • Leo

    I meant to type can affect time, not effect time. You guys are good about calling that stuff out.

  • Hannes

    Time might be a by-product of entropy, just like gravity.

  • Lawrence B. Crowell

    I have found the following lectures on the foundations of quantum mechanics to be very interesting.

    http://pirsa.org/10050055

    P. Goyal uses fairly elementary language here, where he ties logic of quantum mechanics to its algebraic foundations. This discusses on a logical level based on Stern-Gerlach experiments about “what we are doing.”

    Entropy, S, and the second law, dS/dt >= 0, seems to suggest an arrow of time. There is the grand question of how it is that universe started out in a very low entropy state. If the universe emerged from a vacuum fluctuation in another universe the entropy would have been very low. The inflationary bubble which ensued also has a low entropy as a pure state. However, once it inflated beyond a horizon length there was set in a reheating period and the break up or decoherence of quantum fields across the horizon. The universe transitioned from this inflationary de Sitter spacetime to a Freidmann-Lemaitre-Robertson-Walker configuration. Curiously, the universe appears to be transitioning back to a de Sitter state. To understand this in full detail the Bousso bound, which is a holographic version of cosmology, is needed.

    LC

  • Kopdogg1982

    I think that time is really just the process of decay. Like the life and death of the universe, and the process within. That theres more to the universe as a living whole. Such as the universe in itself as a living through the origin of life itself or through blackholes. But the universe living as life of an individuality through time of the whole scheme of things. But in a sense, would time itself ever come to stop. As in all life itself. Would it in a sense cease to move, or exist. Can time itself ever stop. Everything dies. Its apart of living. Like blackholes gravitate reality of life and create time through existince of life. A process of evolution and decay. I wonder how far the universe is truly in the process of life and decay in the grand scheme of things. What more can we expect to see through the evolution process. We can make time what ever we want it to be through a concious. like a computer turning on and off.

  • Kopdogg1982

    Life is the reason why the universe exists at all. Because someone or something has to see the universe and ask these questions of “how and what?” I dont believe in why because there is never an explaination to why things happen. its just the way things work in reality of time and existince. Why is a question everyone asks and its all a different perception of time and space.

  • Kopdogg1982

    Why in science is a good question. But not when it comes to the human mind. We dont get why sometimes and why never needs an explaination when it comes to us. But there always seems to be that question why?

  • Aodhhan

    If time does not exist, then ‘rate’ does not either. Which means, there are no differences is wavelengths, cycles, etc.
    Everything would automatically be in sync, and stay this way; something which we know not to be true.

  • Duncan Ivry

    Leo: “gps sattelites had to be calibrated to include the effects of gravity on time”

    According to the theory of relativity, satellite clocks are slowed down by their orbital speed and accelerated by being in a weaker gravitational field. If corrections were not made, positioning errors would increase at the rate of around 10 km per day. Additionally a transformation between two coordinate systems has to be applied: from the inertial system of the GPS to the system where the GPS-signals are used; the latter coordinate system is fixed and centered to earth and is rotating with “us”.

    This is Einstein’s theory of gravity at work in our everyday, smart-phoning life.

    Should we consider these phenomena being effects of gravity on *time*? Or better on clocks? You know, clocks are special devices in physics, important down to the foundations of this science. We could very well say — and physicists do this –, that time is slowed down for the GPS sattelites, or generally for moving objects. This affects our everyday life. Somebody could take this as time being “real” … and Elvis is leaving the building of science.

    Leo: “If gravity can effect time, doesn’t that prove that time exists in a physical sense?”

    Just as you want. And I’m serious. It doesn’t make any difference, and in those cases physicists restrain from making assumptions.

  • Lawrence B. Crowell

    I actually bent metal on the problem of clock synchronization with respect to GPS satellites. The relativistic effects can cause a drift between clocks on the order of a billionth of a second per second. These effects are both due to the velocities of satellites and their position in the gravity field. If you multiply this drift by the speed of light this amounts to a .3cm distance drift per second. Now this drift will grow with time so it adds up to a meter per hour.

    Time is in some ways strange, and it is not a distance in the same sense of what is measured by a ruler. However, everything is actually moving at the speed of light. Just sitting in your chair you by x = ct are moving a distance along this fourth dimension with time. Time in the pseudo-Euclidean form of spacetime has a different signature than ruler distances, and by means we do not completely understand we perceive this fourth dimension in a different way.

    I have been a bit amused by those who insist that time does not exist. We certainly behave as if it does and the world be observe evolves according to what we call time. It is also an odd question to ask whether time exists. Science is not really about asking whether things exist, but defining various things in operational ways and then understating relationship between them.

    LC

  • Drunk Vegan

    Personally I think that time is simply a measurement of motion. We can only measure the “present” because of our relatively limited perception, but all “timeframes” – past, present, and future, are occuring simultaneously. The universe is not a series of events, it is all a single event which is happening everywhere and through every moment, all of which is “now.”

    The limitations of only being able to observe one slice of the whole are what make quantum mechanics so bizarre. For example, particles occupying superpositions, and popping into and out of existence every Planck second, making up the quantum foam that is space.

    Where do those particles go? Either they are “leaving” the universe, which is supposedly everything, or they are simply leaving the slice of it that we’re able to observe with our limited perspective.

  • Torbjorn Larsson OM

    Late response, but FWIW:

    Does time exist with the very very small. I.e. Below the Planck length?

    Likely yes, according to those supernova results. Causality and smooth structure which results in those small time differences for photons though traveling across most of the observable universe.

  • Torbjorn Larsson OM

    @ jkudz:

    if the particle’s spin changed without direct observation, wouldn’t the entangled partner’s spin change as well?

    Correct, that is the crux here.

    To understand QM as a correlation you can’t claim that observables exist before observation, merely the wavefunction and its entanglement correlations. (And indeed what would that existence mean, if you can’t observe it?)

    If you want to impress reality to what can’t be observed, you also have to accept instantaneous action.

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