Great Mysteries of Physics: Is Time an Illusion?

Time Physics Artist's Illustration

The nature of time, a concept fundamental to human life but still ambiguous in scientific parlance, is explored in the first episode of the new podcast series, Great Mysteries of Physics.

The first episode of the new podcast, Great Mysteries of Physics, delves into the complex nature of time. Challenging traditional notions of time as absolute, researchers discuss theories suggesting time is relative and intertwined with space, a concept contradicting our subjective experience. The discrepancy could be attributed to increasing entropy in the universe, but why the universe started with low entropy remains a mystery. To resolve this, experts propose additional research including eliminating time from scientific equations and investigating the thermodynamics of clocks.

Without a sense of time, leading us from cradle to grave, our lives would make little sense. But on the most fundamental level, physicists aren’t sure whether the sort of time we experience exists at all.

This is the topic of the first episode of our new podcast series, Great Mysteries of Physics. Hosted by me, Miriam Frankel, science editor at The Conversation, and supported by FQxI, the Foundational Questions Institute, we talk to three researchers about the nature of time.

Scientists long assumed that time is absolute and universal – the same for everyone, everywhere, and existing independently of us. It is still treated in this way in quantum mechanics, which rules the microcosmos of atoms and particles. But Albert Einstein’s theories of relativity, which apply to nature on large scales, showed that time is relative rather than absolute – it can speed up or slow down depending on how fast you are traveling, for example. Time is also interwoven with space into “space-time.”

Einstein’s theories enabled scientists to picture the universe in a new way: as a static, four-dimensional block, with three spatial dimensions (height, width and depth) and time as a fourth. This block contains all of space and time simultaneously – and time doesn’t flow. There’s no special now in the block – what appears to be the present to one observer, is simply the past to another.

But if that’s true, then why is our experience of time moving from past to future so strong? One answer is that entropy, a measure of disorder, is always increasing in the universe. When you run the numbers, explains Sean Carroll, a physicist at Johns Hopkins University in the US, it turns out that the early universe had very low entropy. “[The universe] was very, very organised and non-random and it’s been sort of relaxing and getting more random and more disorganized ever since.” This is likely to create an arrow of time for human observers.

We don’t know why the universe started out with such low entropy, however. Carroll suggests it it may be because we are part of a multiverse containing many different universes. In such a world, some universes would, statistically speaking, have to start out with low entropy.

Emily Adlam, a philosopher of physics at the Rotman Institute of philosophy at the University of Western Ontario in Canada, on the other hand, believes the mystery of why our universe started with low entropy is a problem that ultimately stems from the fact that physics is riddled with assumptions about the time.

“I personally am very much on the side that says time does not flow,” she explains. “This is kind of an illusion that comes from the way in which we happen to be embedded in the world”. Her hunch is that, on the most fundamental level, everything happens all at once – even if it doesn’t appear that way to us.

Adlam argues the best way to understand time would be to remove it entirely from our theories of nature – to strip it out of the equations. Interestingly, when physicists try to unite general relativity with quantum mechanics into a “quantum gravity” theory of everything, time often disappears from the equations.

Experiments could also help shed light on the nature of time, helping to test various combinations of quantum mechanics and general relativity. Natalia Ares, an engineer at the University of Oxford, believes that studying the thermodynamics (the science of heat and work) of clocks may help. “By understanding clocks as machines, there are things that we can understand better about what the limits of timekeeping are,” she argues.


  • Miriam Frankel, Podcast host, The Conversation


  • Emily Adlam, Postdoctoral Associate of the Philosophy of Physics, Western University
  • Natalia Ares, Royal Society University Research Fellow, University of Oxford
  • Sean Carroll, Homewood Professor of Natural Philosophy, Johns Hopkins University

Adapted from an article originally published in The Conversation.The Conversation

13 Comments on "Great Mysteries of Physics: Is Time an Illusion?"

  1. Steven Russell Jeffs | May 22, 2023 at 4:30 pm | Reply

    Time is a man-made concept, evolving from the very basic needs of, the best (time) season to plant a crop, fish a species, have a baby.

    As with ‘time’ being relative to speed of travel, I also believe time is relative to Size.

    The Earth, to humans, seems quite large and takes a lot of time to traverse the terrain. The Solar system, to humans, is a 20 year journey for a satellite.

    In a Universe so vast, the Earth is a mere ‘speck of dust’.

    Now, imagine being the size of a Galaxy.
    The distances for Solar systems and the like would be insignificant.
    Time would (appear) to move at a much slower pace than on the speck of dust.

    I’m not sure if this analogy has conveyed the essence of ‘time being relative to size’ but, hopefully you get my meaning.
    Cheers Steve.

    • Bao-hua ZHANG | May 25, 2023 at 8:22 am | Reply

      According to the topological vortex gravitational field theory, the nature of time is the spin of topological vortex. Therefore, time is a circular arrow, although it has only one direction, any point on the circularity can be the start and end. The absoluteness of time is that each vortex field has its own spin period, while the relativity of time is that different vortex fields may have different spin periods.
      Best wishes for you!

  2. David Ashley | May 22, 2023 at 4:38 pm | Reply

    Anyone who’s read Douglas Adams already knows that time is an illusion – lunchtime doubly so!

  3. 1st off, we’re not waiting to get into eternity… we’re already in it! Now with that said, here’s what time itself is. Time is a Gift from The Almighty. Now this gift is like a bubble that humans dwell in within eternity itself.
    The gift of time to humans has a purpose. It is given to us to
    Get to know Him who gave it, then once we know Him, we’ll begin to Love Him and understand His Love and Purpose for us which is to Love ourselves and others and to Obey and Serve him Along with
    Loving and Serving others.
    Now this gift that operates
    Within Eternity does have an
    Experation Date as we know it now. When we’ve breathed our last,(Gift of Time Experation)
    We then will have to give an account of what we did with the gift to Him who gave it.

  4. JOHN P SORG | May 23, 2023 at 1:33 am | Reply

    Firstly, I would venture to say all physics are local. What works in this part of the galaxy or this part of the universe, might not function the same way in another sector of the universe.

    Where we are is relatively stable, and of course time is based on this planet by the movements contained in our solar system. The days the months the years the seasons and so on and so forth.

    There is no, “when you breathe your last, you’re going to have to pay for your life’s conduct in front of the one who made you.” There is no consciousness after death! Even the scriptures Will tell you that! That is if you really want to find out, rather than just guess!

    What is the purpose of black holes? Or, quasars, or, pulsars, Do gravity waves affect time? And if they do, how! Is dark matter a byproduct of black holes? And if it is, what’s its purpose? And, does it affect planetary or galactic separation and stability?

    These guesses are as good as any, as theoretical as they are, it’s no different than the theories that we’re peppered with constantly from all of these different opines! The fact is, nobody knows.

    Is it a mystery? To us, us being mortal, living a very short lifespan, by time we gain any sort of intellect, we are almost in the grave. Eventually, we would have to go out there! But to go out there, we would have to have a much more expansive lifespan. Or, have our humanoid AI driven helpers do it for us. Although, I highly doubt that would ever happen, because we’d kill ourselves off first.

    Now, scripture does tell you, God put eternity into man’s hearts. And, not in the spiritual realm, but the earthly realm. All you’ve got to do is study your Bible if you believe in that sort of thing. And actually, scripture does make more of a case concerning time and seasons than theoretical opines!

  5. Time is relative. My sister is always late for everything. We call her Auntie Einstein because (somewhere in a parallel universe) she is actually quite brilliant. Here, not so much. Relativity.

  6. If some person says, everyone knows nothing; well then it’s bullsh!t

  7. Especially if this person has a professional or personal theory

  8. If there is no time, then there is no movement. The Universe is in motion, so there is time.

  9. Fixed gravity for you. | May 25, 2023 at 2:25 am | Reply

    For better or worse, WWII decided the question of whether it’s legitimate to imagine that gravity distorts light, so now the effect of gravity is, by fiat, the distortion of time and space. It’s a subtle distinction involving a tiny loss of local realism and a massive craving for an exotic dark matter “halo” that resembles a “tub of fat” unless you “modify gravity.”

    • Fixed gravity for you. | May 25, 2023 at 2:55 am | Reply

      Seriously, with quantum gravity it’s simple.

      There are two things about quantizing universal gravitational information flow, firstly a particle aspect involving most critically availability of the gravity carrier-based concept of “focus,” which is a consequence of retro-reflective coherent action as opposed to the lack of focus available to a fully Newtonian gravity regime, and secondly is a gravity carrier wave-based information “roll” effect available, which is a consequence of a gravity Bosonic carrier fundamental self-cancelling nature finding natural expression in a rotating carrier vector field. This isn’t jargon, so get a normal dictionary if confused and don’t pretend, every word here will in there and used correctly here.

      Some other considerations are tendencies of light, to go with the notion that focused gravity can focus light, and that gravity carriers may moderate light speed and may even moderate gravity speed itself through all density variations demanded of its flows.

  10. Fixed gravity for you. | May 25, 2023 at 3:29 am | Reply

    Just to reiterate and expand, I’m not interested in jargon, not interested in politics or kissing Einstein’s crying relatives, so get a normal dictionary if confused and don’t pretend, every word here from me will be in there and used correctly here. Consider taking an English course, my LSAT score was probably twice yours.

    There’s nothing crazy about rejecting “dark matter” as a legitimate placeholder when honestly gravity is the issue and it’s only by dishonestly can gravity being the issue be ruled out. What’s arguably crazy is a journalistic regime that allows the pretense of placeholding utility in “dark matter” when gravity is at issue.

    Another thing to consider is that, as fun as it might seem, pretending one can’t get a GPS system up and running without general relativity is as crazy big of a journalism-inspired joke as pretending to know how to recalibrate it.

    Side Note: Yes, the world is stacked in opposition but it’s not my problem. Regardless, if you multiply the radius of two protons by the ratio of electric and gravitational effects between them you can get a ripple-like gravitational roll-based halo-scale effect with a roll-completion radius matching a typical spiral galaxy. I mention this because replicating focus and roll in gravitational flows is how a simulated spiral galaxy realistically attains stability in form, in my opinion. If I have to do the simulations myself and obtain the free the time and resources, I will do so, in all likelihood without a grant as getting a grant to flip general relativity on its head is likely impossible.

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