Space - time and the illusion of time

[thegroundhog]

TL;DR

If time is an illusion why would it slow down under gravity or at high speed?

I have just finished reading The Order of Time by Carlo Rovelli and From Eternity to Here by Sean Carroll.
I feel I finally understand that time is simply thermal entropy, but they both also talk about space-time and how time slows under gravity and at high speed. If time is just an illusion as they both purport then why would time go slower or faster in gravity and at speed.
The two arguments can't co-exist.

 

[PeroK]

Time isn't an illusion. Not in physics.

 

[PeterDonis]

Moderator's note: Thread level changed to "I".

 

[Dale]

Time is what clocks measure. If it is measurable, then in what way is it an illusion?

 

[PeterDonis]

I have just finished reading The Order of Time by Carlo Rovelli and From Eternity to Here by Sean Carroll.

Both of these are pop science books, not textbooks or peer-reviewed papers. So you should not expect to be able to learn the actual physics from them. You should look up papers by Rovelli or Carroll if you want to see the actual physical arguments they are making in a form that provides a valid basis for understanding and discussion.

 

[russ_watters]

Maybe, but I'd like to see a quote from either that actually says "illusion" or "is simply themal entropy." That would surprise me.

 

[anuttarasammyak]

I feel I finally understand that time is simply thermal entropy

Based on it you may be able to make a clock. Say a droplet of ink diffuse in water vessel. Inflation of ink color in the water could tell you what time it is.

 

[Julius Ceasar]

Time isn't an illusion. Not in physics.

Mathematical time- A construct created to measure motion
Newtonian time- A space-time non reality
Einsteinian time- A space-time reality

Space and time being two sides of the same thing, both distort in the presence of mass or when relatively accelerated. Physics uses the term "time" as a construct to measure motion AND to describe the reality that is space-time.

Newtonian time is a non reality because it requires a single universal moment for everything to exist in but relativity shows that time dilates so this can not be the case, an accelerated particle being almost suspended in time does not exist at the same time as non accelerated particles.

Einsteinian time is the reality, it replaces the idea of a universal moment with moments that are relative and exist at different times.

 

[PeterDonis]

Space and time being two sides of the same thing, both distort in the presence of mass or when relatively accelerated.

No, acceleration (meaning proper acceleration due to, say, being in a rocket whose engine is firing) does not distort spacetime. You can have an accelerating rocket in flat spacetime.

There will be time dilation between the bottom and top of an accelerating rocket in flat spacetime, but that does not mean the spacetime is curved.

an accelerated particle being almost suspended in time does not exist at the same time as non accelerated particles

I have no idea what you mean by this. It doesn't look like anything that's actually in relativity theory.

Einsteinian time is the reality, it replaces the idea of a universal moment with moments that are relative and exist at different times.

There is relativity of simultaneity in relativity, but "moments that are relative and exist at different times" is not a good description of relativity of simultaneity.

 

[Julius Ceasar]

Perhaps the dual/tri use of the term time is being lost here, the OP says time cannot be both an illusion and a reality at the same time and he is right, the term "time" in minkowski space is a mathematical use so is measuring a rockets acceleration/motion, time isn't this mathematical illusion, not in reality.

Like the OP I have no idea how physics let's the two arguments co-exist, to be clear Peter I am talking about the reality not the illusion, can you take a stance here so I know what you're talking about please.

 

[PeterDonis]

Like the OP I have no idea how physics let's the two arguments co-exist

Before one can even form an opinion on that, one needs to be reading actual physics arguments, i.e., actual physics textbooks or peer-reviewed papers, not pop science books, as I pointed out in post #5.

to be clear Peter I am talking about the reality not the illusion

In the post of yours that I responded to, you were not, as far as I could tell, talking about any valid physics at all, for the reasons I gave in my response.

can you take a stance here

A stance on what? On all the ways that an ordinary language word like "time" can be misused in pop science discussions?

If you mean a stance on whether the actual physical effects referred to in the OP, which can be summed up under the term "differential aging" (i.e., different paths through spacetime between the same events can have different lengths, i.e., elapsed times), of course those effects are real. They've been measured in controlled experiments. Whether you want to use "time" to refer to those effects is a matter of words, not physics.

 

[Julius Ceasar]

A definition of time, real or illusion ?

 

[Ibix]

A definition of time, real or illusion ?

See post #4.

 

[Julius Ceasar]

#4 ok what clocks measure
Mathematical time- A construct created to measure motion
you're stance is time is an illusion
general relativity is in trouble

 

[PeterDonis]

Thread closed for moderation.