Time Without Change

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Argency
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Time Without Change

Postby Argency » Thu Sep 08, 2011 1:42 pm UTC

Hey guys, a question in the theme of the "Universal Beginnings and Entropy" thread that's been floating around. I was wondering what you all think of the idea of time without change, since it's a question that's come up in one of my classes recently and it turned out to be fairly contentious.

Here's the scenario - imagine that all change in the universe stops happening; all events, all interactions, everything. Does it make sense to talk about this as occurring for a period of time (say, ten minutes) or is time unintelligible without change?

I think it's the second option, but what do YOU think?
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Re: Time Without Change

Postby Kang » Thu Sep 08, 2011 1:51 pm UTC

Provided it could happen, how would you ever realise that everything stopped? Your own perception after all relies on that, too.

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Re: Time Without Change

Postby Charlie! » Thu Sep 08, 2011 2:05 pm UTC

Time, as in a coordinate, doesn't care about change.

Science, which requires things to actually make a difference to the world to be real (i.e. Occam's razor), does care.
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Re: Time Without Change

Postby Malconstant » Thu Sep 08, 2011 4:02 pm UTC

Lets do it, it'll be a good mind-body test, put those Rationalists to bed. When everything stops but then our unphysical souls spend 10 minutes wondering what the fuck is going on we'll have some re-working to do when we snap out of it.

Anyway, for a real answer, what Charlie said. This shouldn't be a point of actual contention, it's just a point of people ascribing different meanings to the word "time" and getting all angry and confused over it. As a coordinate, by assumption, time changes by 10 minutes. But it's fundamentally untestable.

Here's a knowledge bomb to drop on your class. What would happen if time moved half as fast, or twice as fast. Would you be able to detect that, or notice/feel the difference? Uh-Oh, turns out presentism doesn't work and our intuitions on time are full of shit. Though SR already told us that.
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Re: Time Without Change

Postby Dopefish » Thu Sep 08, 2011 4:55 pm UTC

If in the next instant every single particle in the universe was returned to the position it had 2000 years ago, would time have advanced by 1 instant, or instead jumped back to a time 2000 years ago?

The second law of course says that that couldn't actually happen, and thus we have a direction for time, but if it were to occur, one interpretation in which there is an 'absolute' time would say that time just went forward and there just happened to be a fairly extreme shift in the confiuration of particles during that instant. Some interpretations of time would say that the time really was 2000 years ago though, and our notions of time are simply something we assign to particular configurations of matter in the universe.

In that latter sense, one might even be able to go so far as to say that time isn't fundemental, and it's just something convenient we use for calculations, but isn't itself actually 'real'. I have a hard time with that since I want something to divide up the universes configurations and time does that quite well, but for fleeting moments it seems like one could conceivably imagine physics without time. It seems weird and unintuitive and perhaps not a thought worth pursuing, and yet the absence of an absolute time does seeem to suggest that maybe something could be done, maybe.

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Re: Time Without Change

Postby mfb » Thu Sep 08, 2011 9:33 pm UTC

Argency wrote:imagine that all change in the universe stops happening

Try to define "stops", and you get your answer from that definition.
If you get something to say "it stopped", time passes.
If you do not, nothing stops and there is no question what times does.

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Re: Time Without Change

Postby Argency » Fri Sep 09, 2011 2:50 am UTC

Charlie! wrote:Time, as in a coordinate, doesn't care about change.

Science, which requires things to actually make a difference to the world to be real (i.e. Occam's razor), does care.


I'd argue that not just [science] but [epistemology] and, for that matter, [the poster named Argency] are all elements of [the set of things which require something to actually make a difference to the world to be real]. :P I mean, otherwise we're swimming in Russel's Teapots.
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Re: Time Without Change

Postby Gaelic rock » Fri Sep 09, 2011 11:53 am UTC

I have, in the past, wondered something similar. If time were to travel backwards a short distance, then forwards again, and all particles were subject to this,we would have no idea or memory of such a phenomenon.
Kind of like; time travels in both directions at all possible speeds, but we only remember the past and therefore, only experience it travelling one way.
Does that make sense to anyone else?
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Re: Time Without Change

Postby Technical Ben » Fri Sep 09, 2011 3:16 pm UTC

Malconstant wrote:
Spoiler:
Lets do it, it'll be a good mind-body test, put those Rationalists to bed. When everything stops but then our unphysical souls spend 10 minutes wondering what the fuck is going on we'll have some re-working to do when we snap out of it.

Anyway, for a real answer, what Charlie said. This shouldn't be a point of actual contention, it's just a point of people ascribing different meanings to the word "time" and getting all angry and confused over it. As a coordinate, by assumption, time changes by 10 minutes. But it's fundamentally untestable.

Here's a knowledge bomb to drop on your class. What would happen if time moved half as fast, or twice as fast. Would you be able to detect that, or notice/feel the difference? Uh-Oh, turns out presentism doesn't work and our intuitions on time are full of shit. Though SR already told us that.


You don't move time. Just as you don't move space. You have to move the objects in it. So, if all objects move twice as fast... twice as fast relative to what? Without a universal measure, we can only measure relatively. We cannot define "twice as fast" without defining first the "relative to" bit. :)

So time does not move in both directions. Unless you can prove the matter, objects and everything else relative to you is also doing the same.
Last edited by Technical Ben on Fri Sep 09, 2011 3:30 pm UTC, edited 1 time in total.
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Re: Time Without Change

Postby Xanthir » Fri Sep 09, 2011 3:22 pm UTC

Technical Ben wrote:
Malconstant wrote:
Spoiler:
Lets do it, it'll be a good mind-body test, put those Rationalists to bed. When everything stops but then our unphysical souls spend 10 minutes wondering what the fuck is going on we'll have some re-working to do when we snap out of it.

Anyway, for a real answer, what Charlie said. This shouldn't be a point of actual contention, it's just a point of people ascribing different meanings to the word "time" and getting all angry and confused over it. As a coordinate, by assumption, time changes by 10 minutes. But it's fundamentally untestable.

Here's a knowledge bomb to drop on your class. What would happen if time moved half as fast, or twice as fast. Would you be able to detect that, or notice/feel the difference? Uh-Oh, turns out presentism doesn't work and our intuitions on time are full of shit. Though SR already told us that.


You don't move time. Just as you don't move space. You have to move the objects in it. So, if all objects move twice as fast... twice as fast relative to what? Without a universal measure, we can only measure relatively. We cannot define "twice as fast" without defining first the "relative to" bit. :)

Careful there. Yes, we *can* tell if all objects moved twice as fast, because of relativity.
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Re: Time Without Change

Postby Technical Ben » Fri Sep 09, 2011 3:31 pm UTC

Oh, I was assuming in double speed universes the speed of light (universal constant, not the particles speed) is also doubled. ;)

Which brings be back to the biggest problem of these forums. Stop jumping definitions! The post I was referring to did not specify a universe subject to double the relative mass. I'm sure there would be a lot more problems to worry about than just "oh, is it double speed?" more like "AAAHHHH I'm being crushed!".* :D




*Yes, I know, it's not that much relative mass. I'm joking!
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Re: Time Without Change

Postby Malconstant » Fri Sep 09, 2011 3:37 pm UTC

Technical Ben wrote:You don't move time. Just as you don't move space. You have to move the objects in it. So, if all objects move twice as fast... twice as fast relative to what? Without a universal measure, we can only measure relatively. We cannot define "twice as fast" without defining first the "relative to" bit. :)


Right. All I'm getting at is that there is that the intuitive model of time in which there is something called the present which carries all existence along the time axis is demonstrably false. So sorry, there is no such thing as the present which moves us forward in time, because the present itself doesn't exist, and the mechanism for moving us in time is nonsensical. I usually state this whole idea by saying (somewhat misleadingly) "time doesn't exist".

Xanthir wrote:Careful there. Yes, we *can* tell if all objects moved twice as fast, because of relativity.

I was talking about a different sense of the word time and fast, I don't know about everyone else, but I get the feeling we're all on the same page here. You don't even need relativity to note that doubling everything's momentum will change things. The way we're thinking about this is to say that: suppose you have a 4D space-time plot of the universe in front of you (3 space + 1 time). It's static, but you can superimpose something like a "present" onto it which "gives the universe life" at that point in time. And then slide that present up and down along the shaft of time (relevant: http://forums.xkcd.com/viewtopic.php?f=46&t=74047). If you move the present faster, that would be time moving faster. But the point that is being made is that the perception of time can't be tied to that present, rather it's tied to our brains. In fact, it can be easily shown that such a model for the present requires a second-dimension of time, for the present itself. And that's a turtle-pile that doesn't end.

Edit: Ah yeah, looks like Ben got confused on that point, good catch.
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Re: Time Without Change

Postby eSOANEM » Fri Sep 09, 2011 4:41 pm UTC

Argency wrote:Here's the scenario - imagine that all change in the universe stops happening; all events, all interactions, everything. Does it make sense to talk about this as occurring for a period of time (say, ten minutes) or is time unintelligible without change?


It depends. Are you just stopping interactions or taking a snapshot of reality and holding the universe in that state? If the former, yes, if you had held various particles at a constant velocity before the jump, you'd see them suddenly jump a distance ahead and you'd be able to calculate the time that interactions (and so your thought process and measurement apparatus) stopped for. If the latter, provided everything was restored then there would be no way to even indirectly observe how long everything had stopped for and so there are no non-arbitrary ways to choose which moments to say a jump occurred at other than to say there are jumps between every moment, as such, any theory incorporating such jumps would either have arbitrary choices (without it producing any observable difference so Mr Occam won't be very happy) or else require it to happen at every moment (but it would still provide no observable differences so Occam will still come and smack people who suggest a theory requiring this without a pretty good reason).
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Re: Time Without Change

Postby Technical Ben » Mon Sep 12, 2011 10:22 am UTC

Malconstant, would you agree movement exists though? So it's not "time" that is moving, it is us. You don't get to move the universe "back" so you don't get to go back in time. The most you can do is move the objects you can exert power/forces over.

We may be able to do nifty little tricks in the lab, and cause past erasure etc on the quantum scale. But could we get the power required to scale it up, let alone the information required to put the matter back in a previous state?
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Re: Time Without Change

Postby PM 2Ring » Mon Sep 12, 2011 2:29 pm UTC

This page looks like a good introduction to the concepts of the "block time" or "block universe" theory.
http://www.ipod.org.uk/reality/reality_block_universe.asp wrote:Two Theories of Time
There are two dominant - and incompatible - theories of time: the tensed theory, and the tenseless theory. The tensed theory of time most resembles the popularly-held view of time. The tensed theory requires there to be a present moment (the "now"), and a distinction between an event in the past, present, and future (an event in the past was real, an event in the present is real, and an event in the future will be real). Notice that the "now" moves. This apparent movement of the "now" is an essential feature of the tensed theory of time.

However, there is a philosophical (and logical) problem to this idea of a moving "now". Put simply, it raises the question which has puzzled philosophers: "How fast does time flow?". If the "now" moves then it must move with respect to some time reference. So is it moving with respect to itself? Surely not. To say "Time moves at the rate of one second per second" is meaningless. Rather, the rate of time flow would have to be measured with respect to some secondary, external time reference. However, in our earlier discussion on general covariance it was stressed that there was no clock outside the universe, so there could not be any such external time reference. It is simply logically impossible for there to be a moving "now". Time does not "flow"!

So what is the alternative? The alternative is to consider a universe in which all of time is laid-out (just as the space dimension is laid-out), and there is no moving "now". All times are equally real: as there is no special "now", there is no distinction between past and future. This forms the tenseless theory of time.

Most physicists would favour the tenseless theory as the most accurate representation of time. It is also called block universe because all of spacetime can be viewed as being laid-out as an unchanging four-dimensional block

Also see http://en.wikipedia.org/wiki/Block_time

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Re: Time Without Change

Postby Pez Dispens3r » Mon Sep 12, 2011 2:30 pm UTC

Charlie! wrote:Time, as in a coordinate, doesn't care about change.

A coordinate in what sense? Longitude is, as a coordinate, dependent on the shape of the earth. Likewise, time is dependent on space. If space were to freeze then so would time - they're not independent, but intimately connected.

Instead of thinking of this in terms of change, perhaps it makes more sense to ask whether time would continue if every particle was in its own light cone. In such a circumstance, how could you meaningfully demonstrate that time was passing?
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Re: Time Without Change

Postby Malconstant » Mon Sep 12, 2011 2:46 pm UTC

Technical Ben wrote:Malconstant, would you agree movement exists though? So it's not "time" that is moving, it is us. You don't get to move the universe "back" so you don't get to go back in time. The most you can do is move the objects you can exert power/forces over.

I'm not sure that was a coherent idea. First off, with this level of discussion it's not a given that movement exists in any sense. I could posit that the universe as we know it is just one instant, and it is the one that is occurring riiiiight now. I mean right....now. But it's only one instant and it doesn't change, like a celestial painting.

Also, if I could "move the universe back" (including myself) then I would have no way of knowing that's what I did. It would just be yesterday, and yesterday I wasn't under the impression that I had gone back in time.

What are you basing your claims on? What does it mean to "move the universe back"?, why can't I do it? And why does that mean that I "don't get to go back in time"? I don't think you've thought these ideas through.

Technical Ben wrote:We may be able to do nifty little tricks in the lab, and cause past erasure etc on the quantum scale. But could we get the power required to scale it up, let alone the information required to put the matter back in a previous state?

I don't know what you're talking about, but I do know that the answer is "no, we can't use power to scale up quantum mechanical time-fuzziness to take us back in time. It doesn't work like that. At all. Nothing works like that."

@Mr. 2ring, yup, that's pretty much exactly it. Only you can state it even more strongly as "presentism is demonstrably false". That's what I mean when I say "time doesn't exist"
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Re: Time Without Change

Postby eSOANEM » Mon Sep 12, 2011 3:58 pm UTC

Pez Dispens3r wrote:
Charlie! wrote:Time, as in a coordinate, doesn't care about change.

A coordinate in what sense? Longitude is, as a coordinate, dependent on the shape of the earth. Likewise, time is dependent on space. If space were to freeze then so would time - they're not independent, but intimately connected.


This made me think of another argument for a lack of change implying that time is not meaningful.

If we imagine that we have a probe which is detecting some quantity (air pressure say) around it by looking at the value where it is, then moving in all directions a little bit and measuring the air pressure and we do not know anything about the space we are in; in this case, if we set it off to map the air pressure and their was no variation in a particular axis then any function describing the air pressure could be reformulated in one fewer dimension with that axis removed. It would cease to make sense when talking about translations in that axis as there would be no way of measuring such a translation, in essence, the world the sensor perceives doesn't have that axis.
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Re: Time Without Change

Postby Charlie! » Mon Sep 12, 2011 4:09 pm UTC

Pez Dispens3r wrote:
Charlie! wrote:Time, as in a coordinate, doesn't care about change.

A coordinate in what sense? Longitude is, as a coordinate, dependent on the shape of the earth. Likewise, time is dependent on space. If space were to freeze then so would time - they're not independent, but intimately connected.

Analogies are tricky things, and not to be trusted. Better to keep your thoughts formal when you can.
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Re: Time Without Change

Postby Pez Dispens3r » Mon Sep 12, 2011 4:26 pm UTC

Charlie! wrote:
Pez Dispens3r wrote:
Charlie! wrote:Time, as in a coordinate, doesn't care about change.

A coordinate in what sense? Longitude is, as a coordinate, dependent on the shape of the earth. Likewise, time is dependent on space. If space were to freeze then so would time - they're not independent, but intimately connected.

Analogies are tricky things, and not to be trusted. Better to keep your thoughts formal when you can.

Well, sure. But you're the one who raised the analogy, and failed to keep your thoughts formal. That's why I asked what you meant by coordinate, because you seem to be implying time is somehow separate from the physical universe when a post-Einsteinian understanding of physics would reject that assumption.

After all, as gravity slows photons moving away from the earth, from orbit people on the surface of our planet would appear to be moving in slow motion. But it's not that they appear to be, it's that they actually are: atomic clocks tick faster at higher altitudes because of this effect. According to this understanding, time only moves as the information from other relative points can reach us. As gravity slows down the upper-limit for the transmission of information (the speed of light), time itself slows. With all motion halted (including the motion of travelling photons) time would cease according to our understanding of the physical universe.
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Re: Time Without Change

Postby Diadem » Mon Sep 12, 2011 4:42 pm UTC

PM 2Ring wrote:This page looks like a good introduction to the concepts of the "block time" or "block universe" theory.
http://www.ipod.org.uk/reality/reality_block_universe.asp wrote:Two Theories of Time
There are two dominant - and incompatible - theories of time: the tensed theory, and the tenseless theory. The tensed theory of time most resembles the popularly-held view of time. The tensed theory requires there to be a present moment (the "now"), and a distinction between an event in the past, present, and future (an event in the past was real, an event in the present is real, and an event in the future will be real). Notice that the "now" moves. This apparent movement of the "now" is an essential feature of the tensed theory of time.

However, there is a philosophical (and logical) problem to this idea of a moving "now". Put simply, it raises the question which has puzzled philosophers: "How fast does time flow?". If the "now" moves then it must move with respect to some time reference. So is it moving with respect to itself? Surely not. To say "Time moves at the rate of one second per second" is meaningless. Rather, the rate of time flow would have to be measured with respect to some secondary, external time reference. However, in our earlier discussion on general covariance it was stressed that there was no clock outside the universe, so there could not be any such external time reference. It is simply logically impossible for there to be a moving "now". Time does not "flow"!

So what is the alternative? The alternative is to consider a universe in which all of time is laid-out (just as the space dimension is laid-out), and there is no moving "now". All times are equally real: as there is no special "now", there is no distinction between past and future. This forms the tenseless theory of time.

Most physicists would favour the tenseless theory as the most accurate representation of time. It is also called block universe because all of spacetime can be viewed as being laid-out as an unchanging four-dimensional block

Also see http://en.wikipedia.org/wiki/Block_time

I've never seen the difference between these two theories. Do they give any predictions that are different? Is the distinction in any way meaningful? I don't think it is. It's just meaningless sophistry. It doesn't give us any practical result or distinction whatsoever. At least none that I can see.
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Re: Time Without Change

Postby Malconstant » Mon Sep 12, 2011 5:06 pm UTC

@Dia. The idea of presentism is that we can first imagine a universal 4D space-time graph in which sits everything in the whole damn universe, from all points in time. Now that 4D diagram itself is static, because it already has time as an axis. Presentists contend that a natural intuition on time is ontologically sound. By "natural intuition" I mean the idea that we move in time, and that there is something called the present which "breathes life" into any given instant. That nothing exists meaningfully outside of this present, and the present carries the universe from one moment to the next.

As I said, this is demonstrably false from relativity. It's not even topologically possible to articulate a single universal present given things like black holes. Even if this were not the case, if the present is a thing that moves along the time-axis and gives those moments the privilege of existing, then the issue of "how fast does the present move" is raised. From this is becomes readily apparent that it doesn't matter how fast the present moves, there are no measurable consequences to a change in the speed of the present, it wouldn't feel any different. It turns out that having a present that moves would require its own time axis, and so to include the full picture we now have a 5-D universe (3 space, 2 time). But now if that present is moving in time, then at what rate? The stack of turtles goes all the way down a path of infinity dimensions of time. And that is infinity more than Occum's razor would like.

So presentism is not merely demonstrably false, but it also falls victim to implying infinity dimensions of time. That's the distinction.

The other theory of time considers the idea of a present to be fundamentally unnecessary to describing our experience with time. It stops with a 4-D universe and says that's good enough. And it is.
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Re: Time Without Change

Postby Technical Ben » Mon Sep 12, 2011 9:04 pm UTC

Never mind Malconstant. you would not notice if I was agreeing with you. ;)

Lets just say, with relativity in the equation, there is no universal "time" to move back to. I have no idea why you are questioning what "move back to" means. As this entire thread is about moving "back" in "time" and my example was it made as much sense as moving back in "space". Which I was agreeing was an incorrect way of thinking. :roll:
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Re: Time Without Change

Postby Charlie! » Tue Sep 13, 2011 3:08 am UTC

Pez Dispens3r wrote:
Charlie! wrote:
Pez Dispens3r wrote:
Charlie! wrote:Time, as in a coordinate, doesn't care about change.

A coordinate in what sense? Longitude is, as a coordinate, dependent on the shape of the earth. Likewise, time is dependent on space. If space were to freeze then so would time - they're not independent, but intimately connected.

Analogies are tricky things, and not to be trusted. Better to keep your thoughts formal when you can.

Well, sure. But you're the one who raised the analogy, and failed to keep your thoughts formal. That's why I asked what you meant by coordinate, because you seem to be implying time is somehow separate from the physical universe when a post-Einsteinian understanding of physics would reject that assumption.

[some reference to general relativity]

You're being a bit rude.

Anyhow, in general relativity there are two "times" - proper time, the time measured by a clock, and coordinate time, the fourth (or 0th) dimension of spacetime. When I said "time, as a coordinate," I was talking about, naturally enough, coordinate time.
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Re: Time Without Change

Postby Pez Dispens3r » Tue Sep 13, 2011 3:24 am UTC

Charlie! wrote:You're being a bit rude.

Anyhow, in general relativity there are two "times" - proper time, the time measured by a clock, and coordinate time, the fourth (or 0th) dimension of spacetime. When I said "time, as a coordinate," I was talking about, naturally enough, coordinate time.

Well, so are you: I had to ask you a question twice before you'd give me a response that wasn't completely condescending and dismissive.

From my reading, coordinate time is extrapolated from the recordings of proper time clocks. If proper time clocks have been suspended, how could I measure coordinate time to demonstrate it's still passing?
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Re: Time Without Change

Postby Charlie! » Tue Sep 13, 2011 3:34 am UTC

Pez Dispens3r wrote:From my reading, coordinate time is extrapolated from the recordings of proper time clocks. If proper time clocks have been suspended, how could I measure coordinate time to demonstrate it's still passing?

So the t-coordinate could either be changing or not changing, and you wouldn't know, right? So although having this 4-dimensional space is necessary to write down general relativity and make the correct predictions, it's not uniquely determined by our observations unless you add requirements like "obeys dynamical physical laws."

Or if you look at it another way, there are many 4-dimensional spaces that correspond to what we've seen in the world, and they're all "valid" spaces. To be invalid would require problems more egregious than just violating Newton's laws. But there is going to be one of them that is simplest, that requires the least information to regenerate, and since we can't pull information out of thin air we should use Occam's razor and say we're in that one.
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Re: Time Without Change

Postby Diadem » Tue Sep 13, 2011 4:00 am UTC

Malconstant wrote:@Dia. The idea of presentism is that we can first imagine a universal 4D space-time graph in which sits everything in the whole damn universe, from all points in time. Now that 4D diagram itself is static, because it already has time as an axis. Presentists contend that a natural intuition on time is ontologically sound. By "natural intuition" I mean the idea that we move in time, and that there is something called the present which "breathes life" into any given instant. That nothing exists meaningfully outside of this present, and the present carries the universe from one moment to the next.

As I said, this is demonstrably false from relativity. It's not even topologically possible to articulate a single universal present given things like black holes.

Why? What does GR have to do with anything? There's no single universal present time, but that is not an argument against presentism. The 'present' slice of the universe doesn't have to be straight.

Even if this were not the case, if the present is a thing that moves along the time-axis and gives those moments the privilege of existing, then the issue of "how fast does the present move" is raised. From this is becomes readily apparent that it doesn't matter how fast the present moves, there are no measurable consequences to a change in the speed of the present, it wouldn't feel any different.

If there is no difference then the question is meaningless and thus not relevant. And if you view time as tenseless then you still have to face the same question. Plus the additional question of why we experience a now.

It turns out that having a present that moves would require its own time axis, and so to include the full picture we now have a 5-D universe (3 space, 2 time). But now if that present is moving in time, then at what rate? The stack of turtles goes all the way down a path of infinity dimensions of time. And that is infinity more than Occum's razor would like.

The present moves in both theories though. In one its fundamental to the universe, in the other it's an illusion. But the problem you describe is there in both.

There really is no functional difference between the two theories. It doesn't predict any physical differences. You might argue that it is philosophy not physics, but even in philosophy questions have to be meaningful to be interesting. If it doesn't offer us any knowledge about the universe, no insight into human nature, in how we ought to live or what we ought to do, then the question is pure sophistry, and meaningless. So I reject both positions.

By the way, if you're gonna reply, don't shy away from a formal or mathematical answer. I did 4 master level courses on GR (well, 1 on GR, 2 on cosmology and 1 on black holes), I'm not afraid of going in-depth :)
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Re: Time Without Change

Postby SunAvatar » Tue Sep 13, 2011 6:23 am UTC

To answer the OP: I agree, it looks like "time" is emergent from the structure of the universe, not something fundamental. The idea "Suddenly the whole universe reverts to its state 2000 years ago" is confused, sort of like "Suddenly everything in the universe moves 50 meters to the left" is confused. 2000 years ago is a set of states of the universe, namely those which
  • have about 2000 years less entropy, and
  • are very likely to lead to this one.
This is based on my vague understanding of Barbour's timeless physics, in which the universe is a configuration space and we find ourselves "in" one of these configurations, with any number of continuous paths passing through. Any path along which entropy increases is a sort of "timeline." Some of those timelines flow through this point and others don't, and any blob of configuration space that appears in most of these timelines (in the sense of quantum amplitude) is part of our own probable past or future. This has the weird-but-not-obviously-false consequence that there is no single past any more than there is a single future: if a perfect reasoner with maximal information can only deduce an 80% chance that some past event occurred, that is literally the degree to which it occurred.

This model makes so much sense to me that I'd be kind of disappointed to find out it was false. Then again, I'm unsure whether there's an answer to which of two empirically indistinguishable models of reality is correct. Either offers the same information and it's not as if there's an outside view from which to prefer one, so dropping unnecessary hypotheses is just a matter of parsimony, like eliminating redundant axioms in a theory.
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Re: Time Without Change

Postby Malconstant » Tue Sep 13, 2011 1:27 pm UTC

Diadem wrote:Why? What does GR have to do with anything? There's no single universal present time, but that is not an argument against presentism. The 'present' slice of the universe doesn't have to be straight.

Black hole topology. You literally cannot lay out a bendy-rubbery simultaneous sheet over a black hole. Or you can appeal to regular SR simultaneity. If I'm on the other side of the galaxy and I start running away from you, suddenly your past will be occurring simultaneously as my present. There is really truly no meaningful way in which presentism can hold with either SR or GR.

Diadem wrote:If there is no difference then the question is meaningless and thus not relevant. And if you view time as tenseless then you still have to face the same question. Plus the additional question of why we experience a now.

Yep, that's my point. You'd have to answer the additional question in either case. Here's the answer: our experience of time comes from our brains, which are ultimately chemical beasts whose structure is designed to run on an increase of entropy. Also, we cannot "hold more than one instant of time in our minds at a time", meaning we only live one instant at a time. This is what I mean by the "celestial painting" idea, for all we know there really is only one moment in time, unchanging. I only have the memory of starting to write this sentence because my brain tells me so. All of my conscious experience must be described in terms of my brain. If I feel as though I existed continuously for the past 10 seconds, it's because my brain state gives that sensation.

So "why does time seem to move forward?" Because entropy seems to increase, and our brains are chemical beasts running on the fuel of sugar and entropy. Our experiences developed evolutionarily because there are clear advantages to survival in being able to predict the near future, and make sense of time. I've often wondered if it could be possible for life to thrive off of the decrease of entropy. Although I can't think of an a priori reason why not, their lack of evidence is mighty compelling. But try and think about how you would interact with such an alien, it's trippy.

The present moves in both theories though. In one its fundamental to the universe, in the other it's an illusion. But the problem you describe is there in both.

Yeah, like I said, it's the brain's illusion, and it's clearly evolutionarily motivated, so it shouldn't really be surprising that we see things that way. But you're right, we clearly have a strong built-in intuition of time and of the moving present, so it'd be silly to propose an alternative theory that didn't attempt to address that intuition.

There really is no functional difference between the two theories. It doesn't predict any physical differences. You might argue that it is philosophy not physics, but even in philosophy questions have to be meaningful to be interesting. If it doesn't offer us any knowledge about the universe, no insight into human nature, in how we ought to live or what we ought to do, then the question is pure sophistry, and meaningless.

Granted they don't predict physical differences, but their ontologies are totally different in highly consequential ways. I like to say that this is how you can achieve immortality through fatalism. If time doesn't exist, if it doesn't move and the universe is just static, then my experience of yesterday isn't going to go away. If I had a great time yesterday, then I'm always having a great time because it's always yesterday. Of course that is a "different me" because the me today isn't having the same great time as I was having yesterday, but still.

Again, one should seek to have great times under all ontological frameworks, but with unchanging/eternal consequences, it puts a bit of gravitas on the importance and consequence.

So I reject both positions.

Now that's the first interesting thing I've heard on this topic for a while. Do explain, unless you're going straight up agnostic in the most boring way.

By the way, if you're gonna reply, don't shy away from a formal or mathematical answer. I did 4 master level courses on GR (well, 1 on GR, 2 on cosmology and 1 on black holes), I'm not afraid of going in-depth :)

Aw, see now you should have opened with that so I would have had an appropriate fondness in my response.
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Re: Time Without Change

Postby doogly » Tue Sep 13, 2011 5:41 pm UTC

Barbour's shit is pretty dope. Not my favorite, but he gave a neat talk on it at the FQXi conference I was at.
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Re: Time Without Change

Postby Pez Dispens3r » Thu Sep 15, 2011 3:50 am UTC

Charlie! wrote:
Pez Dispens3r wrote:From my reading, coordinate time is extrapolated from the recordings of proper time clocks. If proper time clocks have been suspended, how could I measure coordinate time to demonstrate it's still passing?

So the t-coordinate could either be changing or not changing, and you wouldn't know, right? So although having this 4-dimensional space is necessary to write down general relativity and make the correct predictions, it's not uniquely determined by our observations unless you add requirements like "obeys dynamical physical laws."

Or if you look at it another way, there are many 4-dimensional spaces that correspond to what we've seen in the world, and they're all "valid" spaces. To be invalid would require problems more egregious than just violating Newton's laws. But there is going to be one of them that is simplest, that requires the least information to regenerate, and since we can't pull information out of thin air we should use Occam's razor and say we're in that one.

I still can't quite understand what you're saying here. I wonder if there's someone else in this thread who does who might explain it better, but perhaps we can break it down a little.

"The t-coordinate could either be changing or not changing, and you wouldn't know it" - you mean in the situation the OP describes, it take it, we wouldn't know if the t-coordinate is changing or not? Ok, agreed. You're then saying four-dimensional space is a convenience for our calculations? Or that it exists independently of our observations? Your wording is pulling me towards different interpretations.

On valid spaces, I take that you mean, say, the four-dimensional configuration of my house is a valid one, as was the configuration ten minutes ago, and that these are two of many valid configurations. That we could do some trippy things to the four-dimensional space that is my house if we were moving it at the speed of light, but it would still be valid. Sure, but that's where you lose me. At what point do I suggest there is a necessity to pull information from thin air? I'm saying that something which can not be measured even in theory, such as the duration of a cessation of all movement (at which point every particle would be inside it's own light-cone, all light-cones being, at that point, infinitesimally small), can not be meaningfully or realistically said to exist.

(I might also remind you that Occam's razor, which you've raised twice, is a tool of reason rather than a proof of scientific concepts. It can be useful for guiding us towards reasonable assumptions, but it can never prove the truth of those assumptions. Further, it can be equally misleading if we're dealing with unintuitive concepts or unknown quantities: it pointed us towards the idea of a sun powered by gravitational collapse, for example, before we had an understanding of nuclear radiation. It's not a stool I'd ever put my weight on, that is, if there were a noose around my neck.)
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Re: Time Without Change

Postby Charlie! » Thu Sep 15, 2011 6:26 am UTC

Pez Dispens3r wrote:On valid spaces, I take that you mean, say, the four-dimensional configuration of my house is a valid one, as was the configuration ten minutes ago, and that these are two of many valid configurations. That we could do some trippy things to the four-dimensional space that is my house if we were moving it at the speed of light, but it would still be valid. Sure, but that's where you lose me. At what point do I suggest there is a necessity to pull information from thin air? I'm saying that something which can not be measured even in theory, such as the duration of a cessation of all movement (at which point every particle would be inside it's own light-cone, all light-cones being, at that point, infinitesimally small), can not be meaningfully or realistically said to exist.

By valid, I mean that it can be described in terms of 4-d spacetime. You know how the square root operation can give you 2 different answers, and so isn't really a function? Not being describable would be sort of like that.

And so if you imagine a space-time diagram (Example), particles exist as lines through space-time. And, say, a block of wood, made from a bajillion particles, looks like a bajillion lines through space-time, arranged like a block of wood. So, question: can "all interactions stop for a while" be represented on a valid space-time diagram? Imagine the block of wood - sometimes the lines jiggle from thermal motion of the atoms, sometimes chemical reactions happen - what does it look like if all interactions stop? Is it describable?

Pez Dispens3r wrote:(I might also remind you that Occam's razor, which you've raised twice, is a tool of reason rather than a proof of scientific concepts. It can be useful for guiding us towards reasonable assumptions, but it can never prove the truth of those assumptions. Further, it can be equally misleading if we're dealing with unintuitive concepts or unknown quantities: it pointed us towards the idea of a sun powered by gravitational collapse, for example, before we had an understanding of nuclear radiation. It's not a stool I'd ever put my weight on, that is, if there were a noose around my neck.)

So you think that we use blue and green rather than bleen and grue as some sort of interesting coincidence, rather than reflecting a general principle? Seems rather unlikely - which is the whole point, not any sort of "proving the truth."
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Re: Time Without Change

Postby Pez Dispens3r » Thu Sep 15, 2011 2:46 pm UTC

Charlie! wrote:And so if you imagine a space-time diagram (Example), particles exist as lines through space-time. And, say, a block of wood, made from a bajillion particles, looks like a bajillion lines through space-time, arranged like a block of wood. So, question: can "all interactions stop for a while" be represented on a valid space-time diagram? Imagine the block of wood - sometimes the lines jiggle from thermal motion of the atoms, sometimes chemical reactions happen - what does it look like if all interactions stop? Is it describable?

No, I don't think it's at all describable. Is this what you've been saying all along? I think our block of wood goes "indescribable" when Everything Stops, because the physical norms which allow us to describe things in the first place have been violated to nonsense. As the x, y and z co-ordinates stop existing for our block of wood, so does the t one.

Charlie! wrote:So you think that we use blue and green rather than bleen and grue as some sort of interesting coincidence, rather than reflecting a general principle? Seems rather unlikely - which is the whole point, not any sort of "proving the truth."

Again you've referred to a phrase which has a background-reading requirement, where it would be difficult to infer that from the context of your post. Here's a deal: if I agree to borrow Fact, Fiction and Forecast from my library, will you explain what you mean here without using jargon? I get enough of that at work.
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Re: Time Without Change

Postby Charlie! » Thu Sep 15, 2011 5:21 pm UTC

Don't bother reading any books on my account - I just figured you'd look it up on wikipedia. If you'd like to promise me to read things, though, you might read this article and any you find necessary to understand it.

Anyhow, in spacetime, a totally non-interacting system would just look like a collection of perfectly straight, parallel lines. Normally, atoms in a block of wood are dancing around, and photons are whizzing off in all directions, which look like twisted, wiggly, and non-parallel lines in spacetime. A bunch of perfectly straight parallel lines would mean that everything was frozen in space for some distance in the time-dimension. That's how "time without change" could be described. The only trouble is that as a hypothesis it's about as useful as "what if, like, it's all a dream?"
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Re: Time Without Change

Postby SunAvatar » Mon Sep 19, 2011 8:25 am UTC

It's pretty obvious that the block-universe concept can model "everything stays really still for a while" as distinct from "no time passes." The question is whether the block-universe concept is correct in making this distinction, i.e. whether the universe is really a block in this sense. I think it isn't; I suspect the OP agrees with me. Then the questions is "well then what model is correct?" and one constraint on the answer is, "Well, whatever it is, if we're claiming it doesn't allow time to pass undetectably, 'time' probably shouldn't be a primitive notion but something that emerges from things like memory and entropy."
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Re: Time Without Change

Postby Charlie! » Mon Sep 19, 2011 9:20 am UTC

You can't have an observed time without some coordinate "t" chugging away in the background, which already has the perfectly serviceable name of "coordinate time" or just "time." Dunno what's so bad about primitive notions. Maybe they're too understandable?
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Re: Time Without Change

Postby doogly » Mon Sep 19, 2011 10:31 am UTC

Time should totally not depend on things like memory. Memory developed at a pretty late time, all things considered. You might want to say that time (a coordinate in the geometry of GR) should be generated by something like a topological quantum gravity theory. Though I and not insignificant others think it more likely that time is primitive, and it's only space that we generate.
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Re: Time Without Change

Postby Malconstant » Mon Sep 19, 2011 2:47 pm UTC

I think there are still different levels being discussed. If by "memory" what is meant is something much broader than consciousness, more like "how physics moves particles around", the point holds. That's the brain-in-a-vat level of discussion which this thread has been wading in. If time can be allowed to move over a duration in which nothing in the universe moves by assumption, that ceases to be a meaningful time. That's the point being made.
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Re: Time Without Change

Postby Charlie! » Mon Sep 19, 2011 8:00 pm UTC

Malconstant wrote:I think there are still different levels being discussed. If by "memory" what is meant is something much broader than consciousness, more like "how physics moves particles around", the point holds. That's the brain-in-a-vat level of discussion which this thread has been wading in. If time can be allowed to move over a duration in which nothing in the universe moves by assumption, that ceases to be a meaningful time. That's the point being made.

Oh yeah, totally useless. But I wouldn't say meaningless. It is a well-formed hypothesis, it's just strictly less probable than the simple explanation. In the same way, "what if our perceptions aren't coming from reality, but are instead generated by an evil demon?" is a totally valid question, it's just that reality is more probable than evil demons by Occam's razor.
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Re: Time Without Change

Postby Malconstant » Mon Sep 19, 2011 9:29 pm UTC

Charlie! wrote:"what if our perceptions aren't coming from reality, but are instead generated by an evil demon?" is a totally valid question, it's just that reality is more probable than evil demons by Occam's razor.

Oh yeah? What's your measure? And never mind the Boltzmann brains.
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