# How does Time move forward?

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May I ask another question - how can one determine that time isn't moving backwards?

jbriggs444
Homework Helper
2019 Award
May I ask another question - how can one determine that time isn't moving backwards?
You can't.

If we arbitrarily re-label the future as the direction of high order and low entropy and the past as the direction of disorder and high entropy then a human being embedded within such a universe will observe an ordered "past" and a disordered "future" as he moves from future to past.

[This is the thermodynamic arrow of time that appears in the reference referred to in post #3 above]

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Buzz Bloom
Gold Member
If we arbitrarily re-label the future as the direction of high order and low entropy and the past as the direction of disorder and high entropy then a human being embedded within such a universe will observe an ordered "past" and a disordered "future" as he moves from future to past.
Hi jbriggs:

This confuses me. If I ignore "arbitrarily", it seems to be saying entropy correlates with increasing order. My limited understanding of thermodynamics tells me that entropy correlates with increasing disorder. Consequently I am guessing that you are saying that you are "arbitrarily" redefining "the future" so that entropy correlates with increasing order.

Regards,
Buzz

jbriggs444
Homework Helper
2019 Award
This confuses me. If I ignore "arbitrarily", it seems to be saying entropy correlates with increasing order. My limited understanding of thermodynamics tells me that entropy correlates with increasing disorder. Consequently I am guessing that you are saying that you are "arbitrarily" redefining "the future" so that entropy correlates with increasing order.
Right. We have a perfectly normal universe with past = order = low entropy over on our left and future = disorder = high entropy over on our right. We flip the whole thing end for end putting the ordered/low entropy part on the right and the disordered/high entropy part on the left. And we paste on new labels for "future" and "past" with "future" still on the right and "past" still on the left.

For us on the outside, we can examine a human's regression from left (relabeled as past) to right (relabeled as future) as if it were a film running in reverse. For him on the inside without being able to see our labels, it is a perfectly normal futureward progression instead.

If you think about it 'time' is a 'consequence' of an object's existence and it's relative speed in 'this' physical universe.

'Time' is not observable until an object shows up in this universe. To answer your question the 'movement of 'time' is not taking place at all. 'Time' is also NOT an illusion which humans defined. Think of it this way, the universe is dying a thermal death, and when the very last electron is left to die time would still be in force and there will be a measurable amount of time from the disappearance of the next of the last electron (if there was anyone there to measure it), until the last electron expires. 'Time' itself may expire in measurable amounts (relatively speaking), but it does not move.
Infact if time would "move" , with respect to what would it do it? With respect to the Time?

--
lightarrow

Buzz Bloom
Gold Member
"How does time move forward?"
Hi Levi:

Since the verb "move" has been explained to be inappropriate, what other verb would you choose to express the concept of your intended question?

How does time advance from past to future?
or
What is physically taking place which corresponds to time advancing from past to future?

Hope this helps.

Regards,
Buzz

To the original question, I reply; why do you think that time moves forward?

We can imagine any physical process drawn out on the space-time graph. A flying bird appears there as a tube of meat in the sky. Nothing changes. Nothing "moves forward".

David

Since the verb "move" has been explained to be inappropriate, what other verb would you choose to express the concept of your intended question?
We need to at least explain what we mean by "move" in this situation. (We encounter a similar problem when distant galaxies "move" at superluminal speed.) "Move" can be a misleading term without further qualification.

phinds
Gold Member
2019 Award
We need to at least explain what we mean by "move" in this situation. (We encounter a similar problem when distant galaxies "move" at superluminal speed.) "Move" can be a misleading term without further qualification.
Which is why it is NOT normal to say that distant galaxies move away from us. The more well-defined (for that case) term is that they recede. Recession velocity is not proper motion, so there is no confusion.

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Out of my own curiosity I've looked at questions that physics can't answer yet, and this one "How does time move forward?" Seemed to be the most interesting to me. Any Theories?
Asking the question as "By what means does time progress" isn't really a question physics would answer. If I were to ask the physicists of the world to answer a question about time, it would be "Does time progress in discreet steps or is there infinitely smaller scales after milliseconds, nanoseconds, picoseconds..."

zuz
According to Wikipedia cosmonaut Sergei Krikalev is 22.68 milliseconds younger then he would have been if he had stayed on Earth.

Buzz Bloom
Gold Member
To the original question, I reply; why do you think that time moves forward?
Hi David:

Unfortunately the OP writer had not participated since the OP, so it is difficult to guess what his intended question meant. For the purpose of post, this is my best guess.
Q: What is physically taking place which corresponds to time advancing from past to future?​
A: As time advances from past to future, entropy increases.​

Do you think that this Q and A is about human perception rather than about the physics of time?

Regards,
Buzz

jbriggs444
Homework Helper
2019 Award
A: As time advances from past to future, entropy increases.
That accounts for a direction -- an "arrow" of time. It does not account for the rate. Lots of physical processes proceed at rates that correlate well with one another. So we calibrate a scale based on this and call it "time".

Buzz Bloom
Gold Member
That accounts for a direction -- an "arrow" of time. It does not account for the rate. Lots of physical processes proceed at rates that correlate well with one another. So we calibrate a scale based on this and call it "time".
Hi jbriggs:

As I read the OP, it is not asking anything about the rate of time changing. My interpretation of the OP is that it is asking for a description of a physical process that implies that time is changing, and the change is in the direction of past to future. I am not completely happy with the answer I gave, and I was hoping for a better description than that. The problem I see with my answer is that if the universe were in a state of equilibrium, then entropy would be stable, and as I described the process, time would not change. Intuitively that seems wrong, but I may be mistaken.

Regards,
Buzz

Do you think that this Q and A is about human perception rather than about the physics of time?
I think that particular question is about human perception, whether it was supposed to be, or not.

Just as this question is about human perception; "Why are the stars so far away?"

We can respond with physics-related reasons why the stars are where they are, but "far away" is the questioner's perception.

David

Hi Levi:

Since the verb "move" has been explained to be inappropriate, what other verb would you choose to express the concept of your intended question?

How does time advance from past to future?
or
What is physically taking place which corresponds to time advancing from past to future?

Hope this helps.

Regards,
Buzz
How time advances from past to future is what I was going for.

It's hard to explain something that doesn't really exist. The presence of a noun "Time" in the language doesn't imply a corresponding real-world entity.

But, having a general idea of what you're asking, I will try to give you an insight.

Imagine if "time" didn't always move forward, but looped around such that we would eventually repeat the past. You would either
[1] be completely unaware of this, so you'd still come here and ask the same question,
or
[2] you'd be aware of it, which implies that you would remember the previous loop, which implies that you could take different actions and cause a different outcome this time around, and then "time" would no longer be looping. That's a contradiction. It cannot arise.

David

bhobba
Mentor
This is a far from trivial topic and requires a whole book to discuss it - with no actual answer at the end of it - but of course along the way your understanding of the issues involved is deepened. I think there are a couple of books on it - the one I recently read is the following:
https://www.amazon.com/dp/0393285235/?tag=pfamazon01-20

My advice is before discussing this topic to become acquainted with the issues involved from a book like the above.

Bottom line is in physics the best definition of time is it is what a clock measures. Go into it deeper - eg the relation of time and entropy - and at the end of it you are aware of a lot new and interesting things - but nothing really is resolved - its still - time is what a clock measures. Time, like space and other foundational things in physics is quite difficult to pin down, beyond simple, almost trite statements.

Thanks
Bill

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