# Why does time require matter ?

by phinds
Tags: matter, require, time
P: 226
 Quote by DaveC426913 No. The process is reversible, and energy is conserved. It is just an unlikely sequence events events given entropy.
My remark about additional energy was referring to the energy 'lost' when the cue strikes the ball producing a sound. In order to physically reverse the process that energy needs to be put back into the cue. While this is mathematically a reversible process, physically I know of no process that would allow it, anymore than the embers of a fire can regain the radiated heat. I consider these things beyond unlikely.
P: 235
If you want to measure the passage of time, you can use a clock.
So far as I know, a clock must be a physical entity made of matter.
If you assume no matter, there can be no clocks, so no way to measure the passage of time.

 Quote by minio Maybe stupid question, but if time is dependent on matter would there be time, if there are only photons? Or are they considered matter in this case?
I cannot think of a way to make a clock out of photons alone.

On the other hand, the expansion of the universes reduces the temperature of the CMBR.
You might be able to get a rough measure of cosmological time this way.
PF Gold
P: 6,353
 Quote by gendou2 If you want to measure the passage of time, you can use a clock. So far as I know, a clock must be a physical entity made of matter. If you assume no matter, there can be no clocks, so no way to measure the passage of time. .
Which is EXACTLY what I said in the original question that started this thread. What's your point? My question is NOT whether we can measure time under the stated condition but whether or not it exists if it can't be measured. In all practical terms, it's a useless question, but it's my question non-the-less.
P: 40
 Quote by phinds I'm not exactly sure what you have in mind with that, but it seems to overly trivialize time.
The point is that time cannot be demonstrated to exist independent of the physical processes by which we claim to measure it and therefore the concept of time as an independent phenomenon doesn't have any scientific basis. This is not an attempt to trivialize time but to attribute to it only those characteristics that have an empirical foundation. Think of it as the Occam's Razor approach, minimizing extraneous assumptions
P: 40
 Quote by salvestrom @budrap: Time is part of the way we measure the seperation of events. Whether we use human inventions such as the second, or simply say 'it took awhile', these things relate to an actual property of the universe that exists regardless of how we describe it.

The assertion that time is "an actual property of the universe" as opposed to a property of material processes lacks, I believe, any empirical support and therefore isn't really scientifically substantive.
PF Gold
P: 6,353
 Quote by budrap The point is that time cannot be demonstrated to exist independent of the physical processes by which we claim to measure it and therefore the concept of time as an independent phenomenon doesn't have any scientific basis. This is not an attempt to trivialize time but to attribute to it only those characteristics that have an empirical foundation. Think of it as the Occam's Razor approach, minimizing extraneous assumptions
I can't see it that way, somehow. It seems pretty much like you're saying there IS no such thing as time (I don't think that's what you are saying, but I don't know how else to describe my reaction). I like Dave's post #13, but it doesn't invalidate your point of view.
P: 15,319
 Quote by salvestrom My remark about additional energy was referring to the energy 'lost' when the cue strikes the ball producing a sound. In order to physically reverse the process that energy needs to be put back into the cue. While this is mathematically a reversible process, physically I know of no process that would allow it, anymore than the embers of a fire can regain the radiated heat. I consider these things beyond unlikely.
Precisely. That is what defines the direction of time. We do not see shards of glass leap together then back onto a shelf where they nudge a person's elbow.

The pool cue and break is analogous to the universe right now. Low entropy, clear direction of time.

The pool table after ten minutes is analogous to the universe trillions of years from now. Very high entropy, no direction of time.

I film the billiard table on a video camera for ten minutes. I play it back to you but only the last minute - and I don't tell you whether I play that minute forward or backward. Can you tell by looking at that minute which direction I played it? Nope.

(Note, by the way that it works whether or not you include friction. If you allow friction then, after 9 minutes all the balls are motionless - no direction of time. If the billiard table and balls are frictionless, then after 9 minutes they are still careening around completely randomly. Either way you have lost the arrow of time in the video I show you. The universe, being a closed system, conserves its energy, thus it is equivalent to the frictionless version of the pool table.)

The original point of comparing the universe to the billiards table was that, trillions of years in the future, there are no low-entropy objects such as pool cues or atmospheres. You just have a uniform soup of billiard balls all with random motion. They carom off each other but, since they're all just billiard balls bouncing around, there is no further increase in entropy, no increase in disorder. Thus the arrow of time is lost.

See?
P: 80
 Quote by DaveC426913 . The original point of comparing the universe to the billiards table was that, trillions of years in the future, there are no low-entropy objects such as pool cues or atmospheres. You just have a uniform soup of billiard balls all with random motion. They carom off each other but, since they're all just billiard balls bouncing around, there is no further increase in entropy, no increase in disorder. Thus the arrow of time is lost.
According to the Poincare Recurrence Theorem, the balls on the billard table will return to near to there starting position after a finite amount of time which can be estimated.

As I undertand, Entropy and the 2nd law of Thermodynamics are relative to an observer. I'm not sure if there can be an observer in a matterless universe, but I would assume events continue to occur separated by time weather observed or not because I personally assume that the moon still exists even if I am not looking at it.

I guess that weather or not time needs matter ends up a bit like asking if a tree falls in the forest and nobody is around to hear it, does it make a sound. I depends on how you define time for one thing.
P: 64
 Quote by budrap The assertion that time is "an actual property of the universe" as opposed to a property of material processes lacks, I believe, any empirical support and therefore isn't really scientifically substantive.
So do you believe the same goes for space?
P: 15,319
 Quote by lukesfn According to the Poincare Recurrence Theorem, the balls on the billard table will return to near to there starting position after a finite amount of time which can be estimated. As I undertand, Entropy and the 2nd law of Thermodynamics are relative to an observer. I'm not sure if there can be an observer in a matterless universe, but I would assume events continue to occur separated by time weather observed or not because I personally assume that the moon still exists even if I am not looking at it. I guess that weather or not time needs matter ends up a bit like asking if a tree falls in the forest and nobody is around to hear it, does it make a sound. I depends on how you define time for one thing.
Now that I think about the far, far future where the universe is just a lukewarm homogenous soup, I can begin to conceive of a universe where time is ambiguous. If nothing evolves from one state to another, then what does it mean to have time pass?
P: 226
 Quote by DaveC426913 Now that I think about the far, far future where the universe is just a lukewarm homogenous soup, I can begin to conceive of a universe where time is ambiguous. If nothing evolves from one state to another, then what does it mean to have time pass?
This is the crux of it really. Many posters here argue time hasn't every really existed, but noone's been brave enough to try and explain the chronological seperation of events. Others are suggesting that it exists currently, but won't in a future where nothings occurs and nothing can record it. Your post is something of a middle ground. It might exist, but is it really relevant?

Perhaps we can consider a seperate space in a potential multiverse where beings have discovered how to peer across the void and watch other 'universes'. What is their take on the state of our far future? They can still record time via their own watches, but absolutely nothing will happen. I realise the thought leaves a loophole through which we can escape by saying 'well, as long as time passes somewhere...'.

We should also consider that recording the interval between two non-events is something we do everyday in the present and real world. Particularly when waiting for someone who is late.

In reference to your (dave's) response to the response to the billiard balls. I totally get where you are coming from, but I feel the reality is that there are some seriously complex interactions that we could watch happen and know if it were reversed. Your second point about the far future I also understand and gets right to the heart of the topic... which we seem no closer to resolving, as awesome as it is.

If you'll excuse me, I've decided to go tell Chalnoth quantum mechanics is wrong...
 P: 88 This seems analogous to the big bang. Perhaps there was something before the big bang but if we can't measure any effects from it then it's irrelevant to us and we say that it doesn't exist. It's my understanding that measuring "actual" time, which enables motion, requires an increase in entropy. If the universe is in a state where there is no way to increase the entropy further, then it will be impossible to measure time, and thus it might as well not exist. Then again I'm just a layman so...
P: 80
 Quote by Lord Crc It's my understanding that measuring "actual" time, which enables motion, requires an increase in entropy. If the universe is in a state where there is no way to increase the entropy further, then it will be impossible to measure time, and thus it might as well not exist.
In the second law of thermodynamics, Entropy isn't required to increase, only forbidden to decrease. Also entropy can be calculated differently from different perspectives.

It is possible that the universe could have constant entropy and that we exist in a vacum fluctuation but that wouldn't stop us from measuring time.

What the 2nd law really tells us is that is imposible to observe the passing of time perpetually, regardless of what the universe does, entropy will get you in the end. It's not possible to live for ever. So, perhaps it's accurate to say that time might as well not exist after you die.
P: 124
 Quote by salvestrom recording the interval between two non-events
Would be a nifty trick, wouldn't it?...

OCR
PF Gold
P: 6,353
 Quote by Lord Crc This seems analogous to the big bang. Perhaps there was something before the big bang but if we can't measure any effects from it then it's irrelevant to us and we say that it doesn't exist. It's my understanding that measuring "actual" time, which enables motion, requires an increase in entropy. If the universe is in a state where there is no way to increase the entropy further, then it will be impossible to measure time, and thus it might as well not exist.Then again I'm just a layman so...
The is at the heart of my question, which, after all this discussion I am beginning to see as more of a philosophical one than a physical one (I'm not happy about this). My question is not and never has been whether or not time can be measured (I agree it cannot) or whether or not it has any effective meaning (I agree it does not), in the far-future scenario. My question has been, and remains, does it EXIST --- does it in some physical sense continue to "flow" as it now is flowing. Turns out, as can be seen in this thread, that's not as simple a question as I had hoped and is apparently more philosophical than I would have preferred.
 P: 38 Saying that time ceases to exist is just a scientific cop-out. Just because it can't be perceived doesn't mean it doesn't exist. If it ceases to exist, then how does it renew? How did it begin in the first place? It just spontaneously came into existence? Rubbish! I can't think of anything in nature that is not ultimately cyclical. Every time I think about questions such as this (the beginning or end of existence), it inevitably leads me to conclude that time and space are infinite.
 P: 53 the flow of time is an illusion perceived by an observer to make sense of his or her conscious perception of change. Time is not intrinsic to the universal laws of nature, rather it is intrinsic to the human psyche. It is simply a concept used in the human mind to explain the passage of one event to another. It is a tool that we use to describe the motion of 'stuff' in the universe. Time does not exist.
P: 124
 Quote by phinds My question has been, and remains, does it EXIST --- does it in some physical sense continue to "flow" as it now is flowing.
No, in the condition you describe in your first post, time does not exist.

At least, according to...
 Quote by Albert Einstein People before me believed that if all the matter in the universe were removed, only space and time would exist. My theory proves that space and time would disappear along with matter.

http://en.wikipedia.org/wiki/Hole_ar...27s_resolution

OCR

 Related Discussions Introductory Physics Homework 5 Cosmology 2 Academic Guidance 4 High Energy, Nuclear, Particle Physics 4 General Physics 40