# Is Time an illusion? **URL:** \ **Category:** Factual Questions\ **Created:** [September 2, 2010, 2:21pm UTC](https://boards.straightdope.com/t/is-time-an-illusion/552385 "2010-09-02T14:21:18Z")\ **Posts on this page:** 20\ **Page:** 3
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 2, 2010, 8:15pm UTC](https://boards.straightdope.com/t/is-time-an-illusion/552385/41 "2010-09-02T20:15:03Z")
Quoth **Meatros** : > [@](#): > > The B theory makes sense out of relativity and simultaneous presents, whereas the A does not. This is, in my view, the selling point of this view. No, relativity makes sense out of relativity. From what I read of those philosophers, they’re making nonsense out of it. Quoth **DSeid** : > [@](#): > > There is also the concept of Plank time. Literally that is the unit of time that it takes light to travel one Plank length and the math is such that any event shorter than that can be said (by some theoreticians) to not exist. So the present becomes the past in one Plank time. The Planck units get way overhyped. We don’t know whether spacetime is quantized, and even if it is, it may well be in a manner much more subtle than a simple grid. And even if spacetime is quantized in a simple manner, we don’t know what scale it’s quantized on. All the Planck time (or Planck length) is, is a plausible back-of-the-envelope guess for what the quantization scale might be in the general vicinity of, if spacetime has a quantization scale at all. ---
**Author:** ![Yllaria](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yllaria/32/3452_2.png) [@Yllaria](https://boards.straightdope.com/u/Yllaria)\ **Post date:** [September 2, 2010, 8:29pm UTC](https://boards.straightdope.com/t/is-time-an-illusion/552385/42 "2010-09-02T20:29:46Z")
> [@DSeid](#): > > There is also the concept of Plank time. Literally that is the unit of time that it takes light to travel one Plank length and the math is such that any event shorter than that can be said (by some theoreticians) to not exist. So the present becomes the past in one Plank time. > > Terry Pratchett had fun with the idea that within that time unit the universe is literally destroyed and recreated in a never ending series of single static moments that we then perceive as travelling through with continuity. And Douglas Adams had the Whole General Sort of Mish Mash (if I quoted that correctly), within which different beings perceive different bits. (Oh, so you see time as going THAT way, kind of thing.) It may be time for me to read that again. There’s good news and bad news about having a bad memory. The good news is that when you read it again, you get to discover it all over again. ---
**Author:** ![Meatros](https://avatars.discourse-cdn.com/v4/letter/m/b4bc9f/32.png) [@Meatros](https://boards.straightdope.com/u/Meatros)\ **Post date:** [September 2, 2010, 8:32pm UTC](https://boards.straightdope.com/t/is-time-an-illusion/552385/43 "2010-09-02T20:32:25Z")
> [@Chronos](#): > > No, relativity makes sense out of relativity. From what I read of those philosophers, they’re making nonsense out of it. Okay, if you believe that, fine. > [@Chronos](#): > > The Planck units get way overhyped. We don’t know whether spacetime is quantized, and even if it is, it may well be in a manner much more subtle than a simple grid. And even if spacetime is quantized in a simple manner, we don’t know what scale it’s quantized on. All the Planck time (or Planck length) is, is a plausible back-of-the-envelope guess for what the quantization scale might be in the general vicinity of, if spacetime has a quantization scale at all. Philosophers are aware of planck time and quantum physics. I’m not sure why you (or DSeid?) believes that this changes anything in the argument. It’s a measurement of how far light travels during this period. The interesting thing is that DSeid suggests that some some theoreticians believe that any event shorter than a Planck length does not exist, which would support the A theory ([presentist theory](http://www.qsmithwmu.com/reference_to_the_past_and_future.htm)): ---
**Author:** ![Tom\_Tildrum](https://avatars.discourse-cdn.com/v4/letter/t/e95f7d/32.png) [@Tom\_Tildrum](https://boards.straightdope.com/u/Tom_Tildrum)\ **Post date:** [September 2, 2010, 8:35pm UTC](https://boards.straightdope.com/t/is-time-an-illusion/552385/44 "2010-09-02T20:35:43Z")
> [@Meatros](#): > > "I should, perhaps, clarify - the passage of time, IMO, is an illusion. Time is a dimension. I don’t understand what this means. Space is a dimension as well, right? Is my sensation of moving through space an illusion? ---
**Author:** ![Indistinguishable](https://avatars.discourse-cdn.com/v4/letter/i/90ced4/32.png) [@Indistinguishable](https://boards.straightdope.com/u/Indistinguishable)\ **Post date:** [September 2, 2010, 8:37pm UTC](https://boards.straightdope.com/t/is-time-an-illusion/552385/45 "2010-09-02T20:37:03Z")
Obviously, there is such a thing as time. The only questions are, what’s it like, and can it be fruitfully explained in terms of something else? ---
**Author:** ![Fuzzy\_Dunlop](https://avatars.discourse-cdn.com/v4/letter/f/848f3c/32.png) [@Fuzzy\_Dunlop](https://boards.straightdope.com/u/Fuzzy_Dunlop)\ **Post date:** [September 2, 2010, 8:37pm UTC](https://boards.straightdope.com/t/is-time-an-illusion/552385/46 "2010-09-02T20:37:45Z")
> [@unravel the mystery](https://boards.straightdope.com/t/unravel-the-mystery/552056/29): > > > [@unravel the mystery](https://boards.straightdope.com/t/unravel-the-mystery/552056/29): > > > > When, people, use, commas, for, no, reason,. > > Commas may be used anywhere in dialogue or exposition to indicate the tempo of speech. I may have to use that over in GD, in the future. Ahh, but if time is illusory then can any of time’s derivative works be real? I think not. Therefore, tempo is also an illusion and the commas were used for no reason. 😉 ---
**Author:** ![Half\_Man\_Half\_Wit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/half_man_half_wit/32/21766_2.png) [@Half\_Man\_Half\_Wit](https://boards.straightdope.com/u/Half_Man_Half_Wit)\ **Post date:** [September 2, 2010, 8:45pm UTC](https://boards.straightdope.com/t/is-time-an-illusion/552385/47 "2010-09-02T20:45:38Z")
> [@Elendil\_s\_Heir](#): > > A dimension could not be an illusion, could it? A hologram’s three dimensional, yet it’s carried on some two dimensional substrate. For certain meanings of ‘illusion’, one could well say that the third dimension is one in this case. ---
**Author:** ![Asympotically\_fat](https://avatars.discourse-cdn.com/v4/letter/a/e47c2d/32.png) [@Asympotically\_fat](https://boards.straightdope.com/u/Asympotically_fat)\ **Post date:** [September 2, 2010, 9:07pm UTC](https://boards.straightdope.com/t/is-time-an-illusion/552385/48 "2010-09-02T21:07:41Z")
What’s a dimension? Seriously, in this context what does it mean to say time is a ‘dimension’? ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [September 2, 2010, 9:16pm UTC](https://boards.straightdope.com/t/is-time-an-illusion/552385/49 "2010-09-02T21:16:38Z")
> [@dracoi](#): > > And I have also heard the idea that the speed of light isn’t so much a cap on speed in the three dimensions as it is an absolute measurement of total speed in all four dimensions. In other words, the sum of the velocities in all four dimensions always comes out to c. Thus, you have time dilation - for things traveling very close to c in the three “traditional” dimensions, they have less velocity left over for traveling through time. Very good discussion on that in Brian Greene’s _The Fabric of the Cosmos_, p. 49\*.\* > [@Brian Greene](#): > > Special relativity declared a similar law for all motion: the combined speed of any object’s motion through space and its motion through time is always precisely equal to the speed of light. At first, you may instinctively recoil from this statement since we are all used to the idea that nothing but light can travel at light speed. But that familiar idea refers solely to motion through space. We are now talking about something related, yet richer: an object’s combined motion through space and time…Moreover, the maximum speed through space is reached when all light-speed motion through time if fully diverted into light-speed motion through space–one way of understanding why it is impossibly to go through space at great than light speed. A good chunk of the book is devoted to the discussion about the flow of time. The entire book\* From Eternity to Here\* by Sean Carroll also addresses the subject. ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [September 2, 2010, 9:20pm UTC](https://boards.straightdope.com/t/is-time-an-illusion/552385/50 "2010-09-02T21:20:17Z")
> [@These are my own pants](#): > > What’s a dimension? Seriously, in this context what does it mean to say time is a ‘dimension’? It means that to describe an exact location you must give coordinates, in x, y, z, and t. If you leave out t, then then you can’t specify the location of a point-sized object. So a physical dimension is one of these four. Other conceptual dimensions exist mathematically but we don’t know of any other physical, macroscopic dimensions required to describe our world. ---
**Author:** ![Asympotically\_fat](https://avatars.discourse-cdn.com/v4/letter/a/e47c2d/32.png) [@Asympotically\_fat](https://boards.straightdope.com/u/Asympotically_fat)\ **Post date:** [September 2, 2010, 9:26pm UTC](https://boards.straightdope.com/t/is-time-an-illusion/552385/51 "2010-09-02T21:26:23Z")
> [@CookingWithGas](#): > > [ > > > [@Brian Greene](#): > > > > Special relativity declared a similar law for all motion: the combined speed of any object’s motion through space and its motion through time is always precisely equal to the speed of light. At first, you may instinctively recoil from this statement since we are all used to the idea that nothing but light can travel at light speed. But that familiar idea refers solely to motion through space. We are now talking about something related, yet richer: an object’s combined motion through space and time…Moreover, the maximum speed through space is reached when all light-speed motion through time if fully diverted into light-speed motion through space–one way of understanding why it is impossibly to go through space at great than light speed. > > A good chunk of the book is devoted to the discussion about the flow of time. The entire book\* From Eternity to Here\* by Sean Carroll also addresses the subject. It’s nice analogy, just I think you got to be careful because Brian Greene does a bit of a switcheroo with his definitions when describing an objects ‘speed in spacetime’ ---
**Author:** ![palindromemordnilap](https://avatars.discourse-cdn.com/v4/letter/p/db5fbb/32.png) [@palindromemordnilap](https://boards.straightdope.com/u/palindromemordnilap)\ **Post date:** [September 2, 2010, 9:30pm UTC](https://boards.straightdope.com/t/is-time-an-illusion/552385/52 "2010-09-02T21:30:04Z")
Jeez, this thread is a waste of … ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 2, 2010, 9:35pm UTC](https://boards.straightdope.com/t/is-time-an-illusion/552385/53 "2010-09-02T21:35:20Z")
> [@](#): > > Other conceptual dimensions exist mathematically but we don’t know of any other physical, macroscopic dimensions required to describe our world. That depends on your definitions. One often has call, for instance, to work in phase space, where there are three dimensions for an object’s position, and three more for its velocity or momentum. And the momentum in such a case is certainly physical, and can be macroscopic. ---
**Author:** ![Asympotically\_fat](https://avatars.discourse-cdn.com/v4/letter/a/e47c2d/32.png) [@Asympotically\_fat](https://boards.straightdope.com/u/Asympotically_fat)\ **Post date:** [September 2, 2010, 9:37pm UTC](https://boards.straightdope.com/t/is-time-an-illusion/552385/54 "2010-09-02T21:37:05Z")
> [@CookingWithGas](#): > > > [@These are my own pants](#): > > > > What’s a dimension? Seriously, in this context what does it mean to say time is a ‘dimension’? > > It means that to describe an exact location you must give coordinates, in x, y, z, and t. If you leave out t, then then you can’t specify the location of a point-sized object. So a physical dimension is one of these four. Other conceptual dimensions exist mathematically but we don’t know of any other physical, macroscopic dimensions required to describe our world. Okay that’s fair enough, I would say that the number of dimensions of an object defined as the number of ordered scalars needed to continiously parametrize it is a fairly decent working definition. but relatvity has been mentioned. In relativity one t coordinate is not necessarily the same as another t cooridinate. Further still you can have weird coordinate systems were the basis vector fields can’t be grouped nicely in to 3 spacelike vector fields and 1 timelike vector field. In the context of relatvity itt doesn’t even mean anything to say time is a dimension except in a vague sense. So perhaps it isn’t such a great description. ---
**Author:** ![Superfluous\_Parentheses](https://avatars.discourse-cdn.com/v4/letter/s/8edcca/32.png) [@Superfluous\_Parentheses](https://boards.straightdope.com/u/Superfluous_Parentheses)\ **Post date:** [September 2, 2010, 9:55pm UTC](https://boards.straightdope.com/t/is-time-an-illusion/552385/55 "2010-09-02T21:55:39Z")
> [@Tom\_Tildrum](#): > > > [@Meatros](#): > > > > "I should, perhaps, clarify - the passage of time, IMO, is an illusion. Time is a dimension. > > I don’t understand what this means. Space is a dimension as well, right? Is my sensation of moving through space an illusion? You **can’t** move through space if the passage of time is an illusion. I think the question in the OP is: is what we perceive as the continual unstoppable progress though the dimension of time (assuming time IS a dimension) actually what happens, and/or do the past and the future exist in some objective way and is “the present” an illusion? On the other hand, I may have just confused the matter even more. ---
**Author:** ![Bad\_Astronaut](https://avatars.discourse-cdn.com/v4/letter/b/e19adc/32.png) [@Bad\_Astronaut](https://boards.straightdope.com/u/Bad_Astronaut)\ **Post date:** [September 2, 2010, 9:58pm UTC](https://boards.straightdope.com/t/is-time-an-illusion/552385/56 "2010-09-02T21:58:39Z")
> [@CookingWithGas](#): > > Very good discussion on that in Brian Greene’s _The Fabric of the Cosmos_ I also recommend this book, that is where most of my ideas on this topic come from. Here is a summary of what I remember (combined with my own ideas): Time itself is real of course, it’s one of the dimensions of spacetime. What is an illusion is the following set of ideas: 1. The past is over and done with 2. The present is happening right now 3. The future is still to be determined. Everything we know about physics tells us that spacetime as a whole simply exists. The future is no more changeable than the past. There is nothing special about any point in time, just as there is nothing special about any particular point or direction in space. However, one unique thing about time is that entropy increases in one direction and decreases in the other. The perception of the flow of time hinges on entropy. We remember the past and do not remember the future due to the effect of entropy on the brain. This makes the future impossible for us to predict, whereas the past can be remembered. What we interpret as the “present” is then the boundary of what is remembered at a particular point in spacetime. At the end of the day, while the flow of time is not occurring in an absolute sense, the effect from our perspective is that it might as well be. But this explanation leaves the door open for finding a region of spacetime where entropy increases in the opposite direction, or building a machine to affect entropy. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [September 2, 2010, 10:08pm UTC](https://boards.straightdope.com/t/is-time-an-illusion/552385/57 "2010-09-02T22:08:54Z")
> [@Bad\_Astronaut](#): > > Everything we know about physics tells us that spacetime as a whole simply exists. The future is no more changeable than the past. There is nothing special about any point in time, just as there is nothing special about any particular point or direction in space. However, one unique thing about time is that entropy increases in one direction and decreases in the other. The perception of the flow of time hinges on entropy. We remember the past and do not remember the future due to the effect of entropy on the brain. This makes the future impossible for us to predict, whereas the past can be remembered. What we interpret as the “present” is then the boundary of what is remembered at a particular point in spacetime. Not arguing with what you say in general, but the past is determinate, and the future isn’t. And we remember the past because it has changed our brains through our experiences, while we haven’t experienced the future yet. That’s how we percieve the flow of time. ---
**Author:** ![Bad\_Astronaut](https://avatars.discourse-cdn.com/v4/letter/b/e19adc/32.png) [@Bad\_Astronaut](https://boards.straightdope.com/u/Bad_Astronaut)\ **Post date:** [September 2, 2010, 10:20pm UTC](https://boards.straightdope.com/t/is-time-an-illusion/552385/58 "2010-09-02T22:20:29Z")
> [@TriPolar](#): > > Not arguing with what you say in general, but the past is determinate, and the future isn’t. And we remember the past because it has changed our brains through our experiences, while we haven’t experienced the future yet. That’s how we percieve the flow of time. You may not think you’re arguing, but your statement directly contradicts the idea that spacetime as a whole exists. Either it’s true or it isn’t, but as I said, the math behind the currently accepted theories of physics suggest that it all exists. If the future exists then it is determined just as much as the past. Predicting the future and remembering the past are equivalent operations in the two different directions of time. Why can we do one and not the other? The same reason that eggs regularly get smashed to bits, but a bunch of egg fragments never seem to converge into a solid egg. Entropy. ---
**Author:** ![Half\_Man\_Half\_Wit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/half_man_half_wit/32/21766_2.png) [@Half\_Man\_Half\_Wit](https://boards.straightdope.com/u/Half_Man_Half_Wit)\ **Post date:** [September 2, 2010, 10:24pm UTC](https://boards.straightdope.com/t/is-time-an-illusion/552385/59 "2010-09-02T22:24:59Z")
Spacetime as a whole may exist, but that doesn’t rule out it being a dynamical quantity – which in general relativity, it is. ---
**Author:** ![barbitu8](https://avatars.discourse-cdn.com/v4/letter/b/839c29/32.png) [@barbitu8](https://boards.straightdope.com/u/barbitu8)\ **Post date:** [September 2, 2010, 10:28pm UTC](https://boards.straightdope.com/t/is-time-an-illusion/552385/60 "2010-09-02T22:28:14Z")
> **[The Paradox of Time: Why It Can't Stop, But Must](https://www.scientificamerican.com/article/could-time-end/)** > > For time to end seems both impossible and inevitable. Recent work in physics suggests a resolution to the paradox > [@](#): > > This grisly prospect was an unanticipated prediction of Einstein’s general theory of relativity, which provides our modern understanding of gravity. Before that theory, most physicists and philosophers thought time was a universal drumbeat, a steady rhythm that the cosmos marches to, never varying, wavering or stopping. Einstein showed that the universe is more like a big polyrhythmic jam session. Time can slow down, or stretch out, or let it rip. When we feel the force of gravity, we are feeling time’s rhythmic improvisation; falling objects are drawn to places where time passes more slowly. Time not only affects what matter does but also responds to what matter is doing, like drummers and dancers firing one another up into a rhythmic frenzy. When things get out of hand, though, time can go up in smoke like an overexcited drummer who spontaneously combusts. So if time is an illusion, so is gravity. You may as well say that reality is an illusion. [Previous page](https://boards.straightdope.com/t/is-time-an-illusion/552385.md?page=2) [Next page](https://boards.straightdope.com/t/is-time-an-illusion/552385.md?page=4)