Time in the reference frame of the photon and aswell curved spac

[Curious45]

Time in the "reference frame" of the photon and as well curved spac

Hi there!

I understand the tendency of physicists to stick to the math, and the logic itself, and to often avoid attempting to conceptualize a process or law, but that's kinda the opposite of what I'd like to do here.

I don't mind at all if you refer to the theory, math or logic, and id quite like that, but I am attempting here to conceptually comprehend the stuff. I am a little math freindly, and very concept, logic and word freindly.

Here, I want to explore the implications of the math, in a thought experiment type manner, and I hope to understand, if, in this thought experiment, the conception valid for the proof/theory/math.

According to what little understanding I have of special relativity, time dilution means that "time" (ie typical "change in the direction of entropy"), slows down as we near the speed of light, the potential implication being that at the exact speed of light, c, time is "fully diluted".

Would it be valid to thus imagine time not existing for a photon, and perhaps all events occurring "simultaneously" for the photon, in its reference frame, according to the theory?

Could we validly imagine light not experiencing change? Or is there some specific reason to think that a photon does "experience" time, while traveling at exactly c?

(This may or may not have implications, it may or may not be testable, or valid, but on the surface it would seem to be an implication given a little thought).

If indeed time does not exist for the photon, then could that imply that time does not exist at all, but only at "low speeds, or lower energy", much like potentially some of the field forces like mass and magnetism?

(Einstein does say that time is relative, and that motion is relative, but also implies that time-space is an objective, if flexable, absolute of sorts which seems slightly at odds)

...

The one other thing I have trouble with in SR, is gravity. If "spacetime" is curved, in the analogy of a warped surface, with a ball rolling down into a hole - the ball would not roll down into the hole if there was not still a force like gravity acting on this warped space.

If you placed a ball in this warped space, there is no force acting on the ball to start it rolling. So it would seem to me, that curved spacetime does not actually explain gravity. Without still have a force, everything would be static unless some force acted on something.

The only verified "proof" of curved spacetime that I am personally aware of is the curvature of light around a gravity well, but that could equally merely be gravity effecting the light, no? Or are there other experimental proofs, outside of the math?

Can anyone give a conceptual version of this theory of gravity, that explains the causation of gravity, in a way that will make sense to anyone?

Thanks so much for your help guys!

 

[Dale]

Would it be valid to thus imagine time not existing for a photon, and perhaps all events occurring "simultaneously" for the photon, in its reference frame, according to the theory?

There is no such thing as the reference frame of a photon. It is a self contradiction.

https://www.physicsforums.com/showthread.php?t=511170

 

[Dale]

The one other thing I have trouble with in SR, is gravity. If "spacetime" is curved, in the analogy of a warped surface, with a ball rolling down into a hole - the ball would not roll down into the hole if there was not still a force like gravity acting on this warped space.

That is a famously bad analogy. Don't lose too much sleep over it. Just search PF for "rubber sheet" to see why.

Regarding proof of curved spacetime, curvature is just tidal gravity, so any measurement of tidal effects is an experimental proof of curved spacetime.

 

[Curious45]

There is no such thing as the reference frame of a photon. It is a self contradiction.

https://www.physicsforums.com/showthread.php?t=511170

Okay fair enough, kinda avoiding the conceptual aspect of this question, but how about this then -is time 100% fully diluted at c?

Or, ill try and put this better -Does "time" make sense, to use to refer to, or is it applied, for massless particles or photons traveling at c?

Is "time" and "travelling at c", together, contradictory or meaningless? (Which really is the essence of the question).

I'm not trying to pretend that light has some kind of experience, or that that would be a scientifically valid POV, I am trying to understand time, and SR in relation to c as a constant.

If there is some state, speed, energy, particle, to which time does not apply, that would be interesting.

It could in theory make time, roughly like potentially mass or magnetism, where it only exists in certain states/energies. Which in itself would seem to question the notion of space-time as even a flexible, absolute, if things exist outside it. Perhaps time being relative, means that time only exists as a relative notion. (It is after all the measure of change in the direction of entropy, it, like space, is a concept that is based on the relative). Of course, logically, the only subjective reference which could exist, would be one inside of time, by the nature of time being change, and the nature of observation being interaction, so that which is outside of time would be essentially permenantly invisible to everything - but it would still have implications, such as potentially determinism.

If light, even though its reference frame is meaningless, because it is timeless, or without time, reaches every point, at the same "moment" it leaves (yes, temporal terms, lol), then that might imply that the entire history and future of the cosmos is already set, conceptually, which kinda flies in the face of uncertainty, even particle/wave duality, to some degree - as the path and decay and life of the photon is identical in respect to "time" as to its creation. Ie, this could have implications for frames of reference that matter.

 

[Curious45]

That is a famously bad analogy. Don't lose too much sleep over it. Just search PF for "rubber sheet" to see why.

Regarding proof of curved spacetime, curvature is just tidal gravity, so any measurement of tidal effects is an experimental proof of curved spacetime.

I will do that now, and see if I can understand where the "impetus"/force/causality comes from, conceptually.

Okay, I did a search on "rubber sheet", and found a bunch of better analogies, diagrams, that don't require "gravity". However, still it doesn't seem to explain the impetus, or causality of the actual movement. If I were to say "put" or create, and object into any kind of model of curved space, there's no reason for it to move without inputing acceleration energy, or a force. Once its moving, then the curving starts to sort of make sense, but without energy or a force, I can see no cause for the acceleration/velocity/energy, in causation terms.

You mean tidal as in the tides of the ocean? If not is there a google or link you could direct me at? Sorry to seem stupid :P

 

[Dale]

Okay fair enough, kinda avoiding the conceptual aspect of this question

It isn't avoiding the conceptual aspect of the question at all. It is simply pointing out that the conceptual aspect is a self-contradiction. A self-contradiction is false, and any reasoning from a false premise is fundamentally fallacious. There is no point in pursuing this line of thought further, it cannot lead to new insights, it only leads to illogical conclusions.

I know that you think that you have stumbled on some deep and mysterious idea that you want to discuss further. Unfortunately, that is not the case. You have simply made a common mistake. There is nowhere further to go in that direction.

 

[Curious45]

It isn't avoiding the conceptual aspect of the question at all. It is simply pointing out that the conceptual aspect is a self-contradiction. A self-contradiction is false, and any reasoning from a false premise is fundamentally fallacious. There is no point in pursuing this line of thought further, it doesn't lead to new insights, it only leads to illogical conclusions.

I know that you think that you have stumbled on some deep and mysterious idea that you want to discuss further. Unfortunately, that is not the case. You have simply made a common mistake. There is nowhere further to go in that direction.

What are you talking about in this last part?

I am simply trying to understand the conceptual implications of SR (also how the heck SR space-time gravity makes any sense if there are no forces involved, how does the object start moving ie.).

I even re-worded this part of my question, so that it did not contain "frame of reference", and simply said, roughly, "how can time be talked about at c or can it not be?", but you just ignored that.

Frame of reference is really irrelevant to the question, so far as I can see. Its impossible to have a timeless frame of reference anyway - a viewpoint requires time, as does conscious observation, or normal comprehension. Frame of reference is basically a null concept regarding timelessness, outside of any specific scientific defination or equation, merely by basic logic.

But that doesn't make it an invalid thought experiment, Einstein's rocket wasn't a real rocket either...Thought experiments don't have to be 100% literally real, in order to provide insight.

Ultimately, the point is, not at all, whether light has a frame of reference or not, but how we can potentially relate the objects at speed c to the phenomena called time, or time dilation, OR not.

And if its "not' that's pretty much an interesting answer in itself I think.

If the line of questioning makes you angry, why not try not just not participate?

 

[1977ub]

If you placed a ball in this warped space, there is no force acting on the ball to start it rolling. So it would seem to me, that curved spacetime does not actually explain gravity. Without still have a force, everything would be static unless some force acted on something.

The only verified "proof" of curved spacetime that I am personally aware of is the curvature of light around a gravity well, but that could equally merely be gravity effecting the light, no? Or are there other experimental proofs, outside of the math?

Can anyone give a conceptual version of this theory of gravity, that explains the causation of gravity, in a way that will make sense to anyone?

Thanks so much for your help guys!

Yes if you search for rubber sheet you will see this recent thread which discusses the limitations of the rubber sheet analogy.

And shows a link to this one which might be more intuitive.

https://www.physicsforums.com/showpost.php?p=4305064&postcount=13

 

[Dale]

Okay, I did a search on "rubber sheet", and found a bunch of better analogies, diagrams, that don't require "gravity". However, still it doesn't seem to explain the impetus, or causality of the actual movement. If I were to say "put" or create, and object into any kind of model of curved space, there's no reason for it to move without inputing acceleration energy, or a force. Once its moving, then the curving starts to sort of make sense, but without energy or a force, I can see no cause for the acceleration/velocity/energy, in causation terms.

Thanks for going through the exercise of looking at previous threads on the topic. It certainly helps to narrow down the question.

In your quote I highlighted a key word. You mention curved space, but in GR it is not just space but spacetime which is curved. That is important for exactly the reason you mention. An object which is at rest in space is still "moving" through time. Since spacetime is curved, some of that motion through time can curve into motion through space. Thus curvature of spacetime can cause an object to accelerate from rest.

You mean tidal as in the tides of the ocean? If not is there a google or link you could direct me at?

Yes, the ocean tides are one type of tidal effect. A tidal effect is present whenever gravity varies from place to place. It is exactly that variation of gravity from place to place which causes the ocean tides.

 

[jtbell]

For a vivid (hypothetical) illustration of the effects of extreme tidal forces, see Larry Niven's science fiction short story "Neutron Star".

http://en.wikipedia.org/wiki/Neutron_Star_(short_story) (summary only)

 

[1977ub]

If people in your original frame measure that you have accelerated to .99c, and measure that your clocks have slowed down to near stillness, you yourself measure light to traveling at c. You will not conclude you have come any closer to the speed of light or the "experience" of a photon.

 

[ghwellsjr]

Or, ill try and put this better -Does "time" make sense, to use to refer to, or is it applied, for massless particles or photons traveling at c?

No.

Is "time" and "travelling at c", together, contradictory or meaningless? (Which really is the essence of the question).

Yes, contradictory and meaningless.

I'm not trying to pretend that light has some kind of experience, or that that would be a scientifically valid POV, I am trying to understand time, and SR in relation to c as a constant.

If there is some state, speed, energy, particle, to which time does not apply, that would be interesting.

Time does not apply at a speed of c.

"how can time be talked about at c or can it not be?"

It cannot be.

You're getting the picture.

 

[Nugatory]

However, still it doesn't seem to explain the impetus, or causality of the actual movement. If I were to say "put" or create, and object into any kind of model of curved space, there's no reason for it to move without inputing acceleration energy, or a force

There's always going to be another "why?" question behind any explanation, so you may never find a reason that's completely satisfactory.

However, here are some considerations that suggest ("considerations that suggest" is a fancy way of saying "hand-waving") that you don't need to look too hard for the impetus behind the actual movement to understand the physics:
1) inertia. If a massive object is already moving, it needs no force to keep it moving.
2) an object that is apparently at rest in space is still moving very rapidly in spacetime; its spatial position isn't changing but it is moving forward in time. (Your wristwatch measures the length you've moved in time the same way that a car's odometer measures the length the car has traveled in space).

So you don't necessarily have to identify any force causing motion through space-time to understand the curvature animations. You just have to accept the unexplained but still quite plausible assumption that everything is already moving forwards in time and if left alone will continue to do so.

 

[Dale]

Frame of reference is really irrelevant to the question, so far as I can see.

Then let me point out all of the places where you implicitly bring in a frame of reference by using a frame-dependent concept:

-is time 100% fully diluted at c?

Time dilation is a feature of the Lorentz transform, a transform between inertial frames.

Does "time" make sense

There are two kinds of time, coordinate time and proper time. Usually the unqualified word "time" refers to "coordinate time". Coordinate time requires a reference frame.

Is "time" and "travelling at c",

Travelling at c refers to a velocity, which is a frame-dependent concept.

It could in theory make time, roughly like potentially mass or magnetism, where it only exists in certain states/energies.

Magnetic fields and energy are also frame-dependent concepts.

eaches every point, at the same "moment"

At the same moment refers to simultaneity, which is a concept requiring a reference frame.​

So clearly it is relevant. You are trying to ask the same illogical statement with different words to see if changing the terminology will make it logical. The problem is the underlying concept is self-contradictory, and those self-contradictory concepts are at the root of all of the other terms that you can use instead of "reference frame" to get the point across.

It is possible to talk about time in any valid reference frame. In any frame a pulse of light in vacuum will have a distinct beginning and a distinct end, both in space in time. There is no such thing as a frame which is moving at c and there is no frame where light is timeless.

But that doesn't make it an invalid thought experiment, Einstein's rocket wasn't a real rocket either...Thought experiments don't have to be 100% literally real, in order to provide insight.

But they do have to be self-consistent, otherwise it is invalid.

If the line of questioning makes you angry, why not try not just not participate?

My pointing out that it is a self-contradiction has nothing to do with anger. I don't know what would make you think that. It is a basic exercise of logic, devoid of emotion, to show that your idea is irrational.

 

[pervect]

You are trying to ask the same illogical statement with different words to see if changing the terminology will make it logical. The problem is the underlying concept is self-contradictory, and those self-contradictory concepts are at the root of all of the other terms that you can use instead of "reference frame" to get the point across.

The problem here as I see it is that curious45 is thinking and talking about physics in a Newtonian context, while trying (presumably) to understand special relativity.

The assumptions Curious45 are making are incompatible with special relativity, presumably due to a lack of a knowledge curious doesn't realize this.

Even after being told :-(

One poster came up with a rather good way to make the issue manifest. That is to point out that when one is taking about the frame of reference of an object, one is really talking about a frame where the object is at rest.

So the "frame" of a light beam woul be the frame where light is at rest. But we already know that one of the assumptions of SR is that light moves at C. So trying to ask about the "frame" where light is at rest just isn't compatible with special relativity.

I don't think the issue can really be made any simpler than that

 

[Nugatory]

Its impossible to have a timeless frame of reference anyway - a viewpoint requires time, as does conscious observation, or normal comprehension. Frame of reference is basically a null concept regarding timelessness, outside of any specific scientific defination or equation, merely by basic logic.

In relativity, "frame of reference" has a specific meaning, and it's not what you're describing above.

A frame of reference is a rule for assigning coordinates to points in space-time (often called "events"), and you're using one any time that you say things like:
- "A and B happened at the same time"; that means that they have the same time coordinate in whatever frame you're using.
- "This object is at rest"; that means that its spatial coordinates (x, y, and z if you're using Cartesian coordinates; but we could use latitude, longitude, and distance from the center of Neptune if we wanted) are not changing as a function of time.
- "A happened one second after B"; that means that B's time coordinate is greater than A's and they differ by one second, using the time coordinates assigned by whatever frame you're using.
- "This object is one meter long"; this is a statement about the difference between the spatial coordinates, in whatever frame you're using, of two points in space-time such that: both points in space-time have the same time coordinate in whatever frame you're using; the path through spacetime (sometimes called a "worldline") of one end of the object passes through one of the points; and the path through space-time of the other end of the object passes through the other point.

You can see why people tend to take verbal shortcuts when talking about this stuff

 

[Curious45]

Thanks for all your in depth answers.

"1) inertia. If a massive object is already moving, it needs no force to keep it moving.
2) an object that is apparently at rest in space is still moving very rapidly in spacetime; its spatial position isn't changing but it is moving forward in time. (Your wristwatch measures the length you've moved in time the same way that a car's odometer measures the length the car has traveled in space)."

Your two explanations here, do give me some understanding of how this may work. Of course, time being what it is, still a bit of a mystery, this isn't a highly conceptually satisfactory explanation, but logically I suppose it may work. Better than what I was working under already.

Although wouldn't this mean that the conversion of energy/momentum from "time" motion, to "spacial motion" would cause the time motion to decrease? If we converted one spatial motion into another that's what would happen, yes?

...

And I now understand why SR has nothing to say about objects traveling at c, in the way I am interested in. The terms and the lorentz equation simply don't apply to light, they are both used to describe the sub-light universe that is more direct to our particular experience, or experience in general. (understandably)

Of course if light were technically "at rest" by being timeless, and we only experienced it as moving, from any form of frame of reference, this sort of lexical and mathematic conflict is one we would expect - and the equations would be specifically not designed to describe it.

This might be perhaps implied by time dilution approaching c, but it is not stated by the current equations, so to infer directly that light is timeless only from the current equations is not appropriate. Got that.

I think therefor I will try and ask another type of question, in another sub forum to the same implication, but without any SR involved. Time is after all change toward entropy, its not some phenomena only explained or understood through SR. Thanks for your time, and patience.

 

[Nugatory]

Although wouldn't this mean that the conversion of energy/momentum from "time" motion, to "spacial motion" would cause the time motion to decrease? If we converted one spatial motion into another that's what would happen, yes?

Remember what I said about "hand-waving" in the earlier post... What it really means is that the analogy isn't perfect and it will break down if you push it too far. At the beginning of this thread you asked for a conceptual instead of a mathematical explanation, and there are a bunch of people here doing a pretty good job of exactly that, but if you want something that you can build new conclusions on, there's really no substitute for the math.

Time is after all change toward entropy, its not some phenomena only explained or understood through SR. Thanks for your time, and patience.

I'm inclined to think that "time is change towards entropy" is backwards; more accurate to say that entropy never goes backwards relative to time in large systems. If you want a definition of time that you can take to the bank, go with Einstein's definition: Time is what a clock measures.

 

[Dale]

Time is after all change toward entropy

Time is what a clock measures.

I am with Nugatory on this. I have never heard the time is entropy definition, and I cannot think of a single clock that uses changes in entropy as its operating principle.

 

[Curious45]

Time is what a clock measures.

Lol, what a meaningless and obtuse definition. Amusing. But then does einstein define time as a dimension of timespace, in SR?

Remember what I said about "hand-waving" in the earlier post... What it really means is that the analogy isn't perfect and it will break down if you push it too far. At the beginning of this thread you asked for a conceptual instead of a mathematical explanation, and there are a bunch of people here doing a pretty good job of exactly that, but if you want something that you can build new conclusions on, there's really no substitute for the math.

If the math is 100% persistantly accurate in all circumstances and situations (dunno if it is, maybe it breaks down in some situations), then perhaps we have the analogy/conception/interpretation wrong...

If the math doesn't work all the time, maybe the whole thing is wrong, conceptually and mathematically, and just happens to work some of the time.

But I agree youve been somewhat helpful, even if this doesn't really help me understand the conceptual implications of the math fully, its better that where I was at the start.

 

[Dale]

Lol, what a meaningless and obtuse definition. Amusing.

Actually, this type of definition is very common and important in physics. In the end, physics is an experimental science, so there must be some way to connect the mathematical quantities in the theory with experimentally measurable quantities. So the most basic and important quantities have definitions like that, instructions on how to measure the quantity.

I define: Mass is what a balance scale measures, distance is what a rod measures, time is what a clock measures. Now I define position as the distance from a reference object and you immediately know how to measure position. I define velocity as the derivative of position wrt time, and you now know how to measure that. Similarly with force and acceleration. Each successive definition becomes experimentally meaningful precisely because of the basic definitions you found so amusing.

 

[Nugatory]

Lol, what a meaningless and obtuse definition.

Read that Einstein quote in context, with all of his explanation and considering of alternatives, and you'll like it a lot more... Or if you still don't like it, at least you'll appreciate just how hard it is to improve on it.

But here is a quick summary of his argument: When we say that "time passes", what does that really mean and how do we know that time is passing?

The answer is that one way or another we are watching some process that evolves over time: The number of gray hairs on my head increases (actually decreasing, but only because it's falling out faster than it's graying); the number of times the pendulum in the grandfather clock has swung back and forth increases; a sample of radioactive material decays; the milk in the refrigerator goes sour; the object that I dropped off the top of a tall building is moving closer to the ground; the hands of my wristwatch are moving; the sand in the top of the hourglass is falling into the bottom half; the candle is getting shorter as it burns; and so forth.

So all measurements of time passing come down to observing a progressive change in a physical system. Therefore, we can choose to define a clock to be any physical system that evolves in a predictable way, as do any of the examples above... and now it makes sense to define time to be what we're measuring with these devices.

One great advantage of this definition is that we can use it to design experiments - if the experiment requires that we know something about how much time has passed, we know to introduce a predictable physical process into the experiment so that we can watch it and say something about how much time has passed.

 

[pervect]

I am with Nugatory on this. I have never heard the time is entropy definition, and I cannot think of a single clock that uses changes in entropy as its operating principle.

Entropy is sometimes said to define the "arrow of time". Overgeneralizing this statement to say that entropy defines time itself is, I think, misguided at best. At worst, it seems cranky.

Maybe we need to remind everyone (especially the OP here) about the PF forum on personal theories. (Emphasis is mine).

Discussion Guidelines

Generally, in the forums we do not allow the following:

Discussion of theories that appear only on personal web sites, self-published books, etc.
Challenges to mainstream theories (relativity, the Big Bang, etc.) that go beyond current professional discussion
Attempts to promote or resuscitate theories that have been discredited or superseded (e.g. Lorentz ether theory); this does not exclude discussion of those theories in a purely historical context
Personal theories or speculations that go beyond or counter to generally-accepted science
Mixing science and religion, e.g. using religious doctrines in support of scientific arguments or vice versa.Links to web sites that fall in the categories listed above will be removed.

Generally, discussion topics should be traceable to standard textbooks or to peer-reviewed scientific literature. Usually, we accept references from journals that are listed here:

 

[Curious45]

a progressive change in a physical system.

That seems to not be terrible different from how I defined it, except I included the thermodynamic arrow of time, which is widely accepted.

Lets add, the arrow of time in:

Time =

A progressive change in a physical system

+

In an isolated system, entropy tends to increase with time (defined as by statistical mechanics, and thermodynamic equilibrium)

(Ie assymetry)

So okay, my "change toward entropy" wasn't specific and wordy enough. Given, I was imprecise. But I don't see how the above combined quotations is contraversial in any way though, or even anything less than obvious.

Any accepted law that applies to time, such as the lorentz tranformation, or the 2nd law, can be used to describe it. Look under time on wikipedia. Beyond that einstein summed it up well:

"a progressive change in a physical system."

Thats really all I said, although perhaps without verbal grace...

 

[Nugatory]

That seems to not be terrible different from how I defined it, except I included the thermodynamic arrow of time, which is widely accepted.

This would be a good time to start another thread, as the thermodynamic arrow is a very different thing in the underlying math (and to be fair, I think you already suggested another thread)

 

[Nugatory]

That seems to not be terrible different from how I defined it, except I included the thermodynamic arrow of time, which is widely accepted.

This would be a good time to start another thread, as the thermodynamic arrow is a very different thing in the underlying math (and to be fair, I think you already suggested another thread). But note that none of the time-dependent processes I describe, with the possible exception of the souring of the milk in the refrigerator, involve an increase in entropy.

 

[Curious45]

This would be a good time to start another thread, as the thermodynamic arrow is a very different thing in the underlying math (and to be fair, I think you already suggested another thread). But note that none of the time-dependent processes I describe, with the possible exception of the souring of the milk in the refrigerator, involve an increase in entropy.

I have started another thread already, and Id be happy if this one were closed now.

I disagree about those examples not included entropy, thermodynamic equilibrium is defined as the tendency to chemical, energetic, mechanical, thermal etc equilibrium. When taken together, every single example involves the 2nd law.

http://en.wikipedia.org/wiki/Thermodynamic_equilibrium

http://en.wikipedia.org/wiki/Second_law_of_thermodynamics

But I digress, again, I am happy if this thread is closed.

 

[Dale]

When taken together, every single example involves the 2nd law.

But they don't use it to measure time. Entropy is something which interferes with the measurements of time, not something that is measured.

I agree that the second law of thermo defines the arrow of time. It does not define time AFAIK. You may feel free to drop the subject or post a scientific reference.

 

[Curious45]

This I guess, to me, this seems more like a matter of lexical or conceptual intepretation of what's accepted and given, as math, theory or observation, rather than something that science or evidence specifically says something against, or for. Like an implication.

Maybe I am wrong, IDK.

I understand however that where this might lead could be speculation, in the terms of this thread/photons etc though.

 

[Nugatory]

This I guess, to me, this seems more like a matter of lexical or conceptual intepretation of what's accepted and given, as math, theory or observation, rather than something that science or evidence specifically says something against, or for.

Entropy has a precise mathematical definition. Use that definition, and you'll find yourself agreeing with DaleSpam.

The "arrow of time" stuff is about using that definition of entropy to explain why some physical processes (a swinging pendulum, for example) can be played backwards to get back to the initial conditions; while others (the eggs are broken, beaten with a fork, poured into the omelet pan, cooked, and eaten) cannot. When it comes to measuring the passage of time, the pendulum is a lot more useful than the pan of eggs. We'll use the pendulum clock to tell us how quickly the entropy of the eggs is increasing with time, rather than using the increasing entropy of the eggs to tell us how quickly the pendulum is swinging.

 

[Curious45]

Entropy has a precise mathematical definition. Use that definition, and you'll find yourself agreeing with DaleSpam.

It can do. The 2nd law itself is not this, the mathematic defination is quantum statistical mechanics attempt to explain the law, but it is not the law in itself.

The "arrow of time" stuff is about using that definition of entropy to explain why some physical processes (a swinging pendulum, for example) can be played backwards to get back to the initial conditions; while others (the eggs are broken, beaten with a fork, poured into the omelet pan, cooked, and eaten) cannot.

The pendulum, as a whole, "closed or isolated" system, cannot be "played backwards", because the energy spent has been equalised already (the kinetic energy, tranformed from the chemical energy we eat for example, if you push it with your hands, or wind up a mechanism has already been equalised)

The constantly swinging pendulum, in any given state, does not tell us how much time has passed, if any, if we encounter it for the first time, or look at it in totally random intervals, unless we carefully track the energy and motion expended/equalized (for example via the clock face).

I don't think the thermodynamic arrow of time is "an explanation". It's something we observe about time, that it runs "forwards" not "backwards" which can be defined precisely by the 2nd law. In that sense, it seems to be more of a feature.

Statistical mechanics offer no actual explanation for why the arrow exists in the direction it functions in, it attempts to explain the 2nd law within time, not the arrow of time itself.

I have heard an explanation of why the arrow runs forward, but its outside the scope of this forum.

Keep in mind, the 2nd law is supposed to apply only to closed or isolated systems. We can't define something that interacts with something else, as being closed or isolated on its own. Mathematical or conceptual abstractions might be misleading here.

 

[chill_factor]

The pendulum, as a whole, "closed or isolated" system, cannot be "played backwards", because the energy spent has been equalised already (the kinetic energy, tranformed from the chemical energy we eat for example, if you push it with your hands, or wind up a mechanism has already been equalised)

The constantly swinging pendulum, in any given state, does not tell us how much time has passed, if any, if we encounter it for the first time, or look at it in totally random intervals, unless we carefully track the energy and motion expended/equalized (for example via the clock face).

Statistical mechanics offer no actual explanation for why the arrow exists in the direction it functions in, it attempts to explain the 2nd law within time, not the arrow of time itself.

1. a pendulum in vacuum is not a dissipative system. It will go on forever. Entropy is staying constant which is allowed in thermodynamics.

2. statistical mechanics does explain the relationship between entropy and time. Its used all the time in chemistry for just that.

 

[Curious45]

1. a pendulum in vacuum is not a dissipative system. It will go on forever. Entropy is staying constant which is allowed in thermodynamics.

Presumably you have not tested this, lol.

A pendulum, alone, in a "vacuum" (vacuum isn't really empty either), in a completely closed system, not only, by its macroscopic movements (because entropy is microscopic too), cannot be used to measure time (because there's nothing converting an energy expendature into a progressive change of some sort, like a clock face, or digital display etc, nor an entropic human memory system to count the ticks), but there is no-one around to take the observe the "measurement" from it either.

This closed system of a pendulum without gravity, mechanical equilibirum, etc, its own center of mass as an object, set in motion, by a theoretical nothing, is basically just a detached mathematical abstraction.

We can't test its reality outside of just math, OR know its relevance to time:

If you could produce a universe, where on the micro and macro scale, entropy was permenantly 100% static with some weird pendulum...could we say there is time? (well no one would be there to say it, lol). We would have no way of defining an arrow of time. And for all intensive purposes, things even changing thusly symmetrically rather than assymetrically, it would also be perpetually cyclic. If we could, without effecting the system take a "picture" at random unknown intervals, we would have no way of how much time had passed.

Personally i get nothing informative or insightful from imagining this abstraction. The 2nd law applies to closed systems, so anything we describe in relation to, say, life here on earth, should be a heck of a lot larger, as a system, than an imaginary pendulum I would think.

statistical mechanics does explain the relationship between entropy and time. Its used all the time in chemistry for just that.

Yes and no, your sort of replying out of the conversational context I seems like. Maybe you were doing the same above, IDK.

Whatever one wants to make of statistical mechanics, it doesn't explain why the arrow of time goes "forward", the whole idea, operates itself within a construct of forward moving time. Thats what I was replying about.

What does attempt to explain, is the broader concept of the 2nd law (which conversely describes the arrow, assymetry, a feature of time, at least time as we know it) in mechanical terms.

The statistical mechanics certainly adds detail in quantum mechanics, and chemistry to the notion of equilibrium, I am just not personally sure if it can be used to describe all the elements of the 2nd law, or not?

At least, I tend to prefer referring to both concepts of entropy, for my idea of entropy, distribution (statistical mechanics), and equilibrium of chemical, mechanical, electrical and energetic etc nature (the 2nd law itself), because, at minimum, the later ideas are easy concepts to check for and think about, without thinking deeply about distribution. Certainly the lack of perpetual motion devices in the real world, or exceptions to the law as written, makes a convenient way to think.

Actually I am curious whether statistical mechanics can be used to explain all/every aspect of the 2nd law? (I guess it probably can, just more difficult to examine each aspect as easily)

 

[chill_factor]

the pendulum in a sealed airless glass chamber is a non-dissipative system. For all intents and purposes it can go on forever. You can then measure rates with this pendulum in a sealed airless glass chamber. It will only emit isotropic blackbody radiation, which results in no net momentum gain or loss. With a magnetically levitated hinge, even frictional losses can go to zero. therefore it is a clock. Time is thus measured by oscillation periods.

I thought too before that (chemical) entropy and time were related. They aren't. Entropy might still be related to time, but not through molecular degrees of freedom. There may be space-time degrees of freedom.

 

[Curious45]

the pendulum in a sealed airless glass chamber is a non-dissipative system. For all intents and purposes it can go on forever. You can then measure rates with this pendulum in a sealed airless glass chamber. It will only emit isotropic blackbody radiation, which results in no net momentum gain or loss. With a magnetically levitated hinge, even frictional losses can go to zero. therefore it is a clock. Time is thus measured by oscillation periods..

Well even in this abstraction (gravity?), entropy, in the form of human memory (A highly entropy dependant process, presumably watching every "tick"), would still be required to measure the passing of time (or some other external entropic system, like a computer and a camera).

A proper clock doesn't just oscillate with no discernable arrow of time/assymetry, it progressively changes.

Imagine you had no memory (not even short term), and the pendulum had no clock face or measurement process. (Lets ignore the rest of the brains reliance on entropy for this scenario). Would the pendulum still measure time? Would we even have a concept of time? (Ill stop there so this is a hypothetical, rather than speculation)

I thought too before that (chemical) entropy and time were related. They aren't.

Well I suppose if its possible to conceive of an entropyless universe, that still changes, perhaps we can ignore the 2nd law, and its relationship to time. But personally I don't understand this is as automatically valid, as there would be no memory or brains (entropy required processes), so no observers and I still can't say whether such a thing could be described of having time, in the sense that our universe has time. It would be pure abstraction of course.

I feel like when I am imagining such things, I am stretching far outside of the bounds of what is knowable, testable or even imaginable. The closed system I operate in (life) has entropy in its progressive changes.

If there was a way of measuring and observing time, without entropy, logically, I might buy into the notion they are not intertwined concepts. But logically I can't conceive of any way that's possible, in fact it seems entirely illogical.

And when I think of situations without any entropy, if indeed that's possible, I can't really think about them having time, in any conventional sense. Even if they move, the only ones that know about it live in entropic systems, and use entropy to measure it, internally these entropyless systems are sort of static, constantly repeating, "time" symmetrical.

I don't want to get into any real concept of what time might be outside of this, but just for me, when I hear about dilution, and the arrow, as being part of the overall, albiet vague, scientific description of time, I take that literally, conceptually, that these are actual qualities of time. I suppose that's interpretive, but it also seems intuitive, based on observation.

Without these types of qualities, like progressive change, entropy, assymetry, dilution, I am not sure that what I subjectively experience as time, could be applied to any other kind of phenomena proposed as also being time-like.

Whether these descriptions are the best ones, or not, is unknown, as it always is with any model or theory, but they are the best we have at the moment. Maybe we would veiw these as more "hand-wavey" models/descriptions of time, or more literal and true ones, without which time as we know it, would not be.

But when people look at say, relativity, they don't just say "this is what things happen to do, but that says nothing about it", they say "this is the nature of the thing", and they say this with great confidence and emphasis. If we have accepted laws and math that describe time, is it so inappropriate to let the laws and maths speak for the actual phenomena?

IDK if mainstream science has anything like a position on this, though I've heard good, logically coherent, accounts of time from individual scientists.