Special relativity - frame of reference

[richrf]

You mean like a birthday party? It's the child's 5th birthday today, so if you wanted to know what year it is on the day of the party you can just add the child's age to his birth date.

If that's your objection then remove the humans from the example and create an example that doesn't involve humans. The physics is the same, either way.

When you state a person's age what you are really doing is declaring the amount of time that has elapsed since their birth. Are you claiming that mechanical clocks can't be used to measure that amount of time?

I am differentiating between measured aging and real biological aging, as in the case of twins.

 

[Ibix]

Would you say this is scientifically proven? Can you point me to a paper on this subject with experimental evidence. I am trying to separate ontological, philosophical speculation from scientifically established evidence.

Can you point to any evidence at all that aging is a non-physical process? One that doesn't depend on chemistry and, therefore, ultimately on quantum theory? If you can't, why would you imagine it obeys different physical laws from everything else?

That would seem to be the extraordinary claim here.

 

[richrf]

Can you point to any evidence at all that aging is a non-physical process? One that doesn't depend on chemistry and, therefore, ultimately on quantum theory? If you can't, why would you imagine it obeys different physical laws from everything else?

That would seem to be the extraordinary claim here.

I am simply asking for evidence that biological aging is affected as is being suggested. I don't believe there is any laws of chemistry that can be used to support this claim. I'm not one to leap without strong evidence and theory.

 

[PeterDonis]

I am simply asking for evidence that biological aging is affected as is being suggested. I don't believe there is any laws of chemistry that can be used to support this claim.

You are wrong. Biological bodies are physical objects. Physical objects obey the laws of physics. The laws of physics, which have been confirmed extensively for objects whose "aging rate" we can measure precisely, say that all objects age according to proper time along their path through spacetime.

I am differentiating between measured aging and real biological aging

Then you are the one who is making a claim without evidence. What evidence do you have that "real biological aging" is not a physical process like any other?

 

[Ibix]

I am simply asking for evidence that biological aging is affected as is being suggested. I don't believe there is any laws of chemistry that can be used to support this claim. I'm not one to leap without strong evidence and theory.

It's really quite simple. All physical processes must run slow by the same factor, as measured by an observer in relative motion, or relativity is trivially and wildly wrong. I already pointed out the evidence that it is not wrong, in the sticky at the top of this forum. So either aging runs slow or it is not a physical process.

 

[richrf]

Thank you all.

 

[victorqed]

I need to read more to understand this. Is not clear to me why acceleration makes the differece but I guess is to soon to ask you here, I'll read some more and if I still don't get it I'll ask you.

Thank you.

 

[m4r35n357]

I need to read more to understand this. Is not clear to me why acceleration makes the differece but I guess is to soon to ask you here, I'll read some more and if I still don't get it I'll ask you.

Thank you.

It doesn't; it is just used to explain how the relative velocity (which does make a difference) is achieved. Draw a spacetime diagram. You will know you have understood it properly when you say to yourself something like "this is just Pythagoras with the sign changed".

 

[Ibix]

Acceleration doesn't make a difference. The path length through spacetime does. The only place acceleration comes in is that you need the paths to cross twice to compare lengths, and in flat spacetime that means one needs to turn round.

 

[victorqed]

This is very interesting and addresses my question, which is solely about biological aging. Can you explain or direct me to a paper that describes how it was determined that someone biologically aged less in space than they would have if they were on Earth? This would be an extremely interesting read. Thank you.

Would you say this is scientifically proven? Can you point me to a paper on this subject with experimental evidence. I am trying to separate ontological, philosophical speculation from scientifically established evidence.

I guess it would be Hafele–Keating experiment

 

[richrf]

You are wrong. Biological bodies are physical objects. Physical objects obey the laws of physics. The laws of physics, which have been confirmed extensively for hi whose "aging rate" we can measure precisely, say that all objects age according to proper time along their path through spacetime.

Then you are the one who is making a claim without evidence. What evidence do you have that "real biological aging" is not a physical process like any other?

Aren't you asking a philosophical/metaphysical question, or has physicalism be proven as a scientific fact? I'm not asking about philosophical viewpoints, I am asking for scientific evidence.

 

[richrf]

I guess it would be Hafele–Keating experiment

Thank you, but I do not believe this addresses my question. I am specifically interested in the experiment that demonstrated that astronauts returning from space aged less than they would have if they remained in Earth. This is the claim that I would like to read about.

 

[m4r35n357]

Thank you, but I do not believe this addresses my question. I am specifically interested in the experiment that demonstrated that astronauts returning from space aged less than they would have if they remained in Earth. This is the claim that I would like to read about.

They age according to the journey time. The journey time is understood. You need to justify why you think they would age differently than their clocks!

 

[richrf]

They age according to the journey time. The journey time is understood. You need to justify why you think they would age differently than their clocks!

I am looking for evidence that biological aging is dependent upon clock measurements. If there isn't any, then that would end my inquiry.

 

[Mister T]

I am differentiating between measured aging and real biological aging, as in the case of twins.

Not in any meaningful way you aren't. Whether one uses "measured aging" or "real biological aging" one gets the same answer. On my 50th birthday the "measured aging" is 50 years, and the "real biological aging" is 50 years. You have a distinction without a difference.

 

[PeterDonis]

I'm not asking about philosophical viewpoints, I am asking for scientific evidence.

I already gave you an answer as regards astronauts: we can't measure biological aging precisely enough. So if that's the only evidence that will satisfy you, it doesn't exist.

 

[richrf]

Not in any meaningful way you aren't. Whether one uses "measured aging" or "real biological aging" one gets the same answer. On my 50th birthday the "measured aging" is 50 years, and the "real biological aging" is 50 years. You have a distinction without a difference.

Two twins can be measured to be of different ages, but are biological the same age, e.g. both have gray hair and aged skin. The question is whether clock measurement observations determine the biological aging process?

 

[PeterDonis]

Aren't you asking a philosophical/metaphysical question, or has physicalism be proven as a scientific fact?

No, and no. You can't "prove" physicalism. So if a proof of physicalism is the only thing that will satisfy you, it doesn't exist.

However, if such proofs are the only thing that will satisfy you, further discussion of the issues you are raising here is pointless, since you refuse to accept reasonable arguments based on the evidence we do have--the same reasonable arguments that convince everybody else that, if you send a clock along with an astronaut, the astronaut ages at the same rate that the clock ticks. And clocks, whose elapsed times we can measure precisely enough, have indeed been sent on the same kinds of trips that astronauts have, and the elapsed times on the clocks match precisely the predictions of GR. All of this is strong indirect evidence that biological aging goes at the same rate as everything else. If you are unwilling to accept that, then, again, further discussion is pointless.

 

[richrf]

I already gave you an answer as regards astronauts: we can't measure biological aging precisely enough. So if that's the only evidence that will satisfy you, it doesn't exist.

Thank you. Can you provide me with a link describing the case of the astronauts. Presumably they were able to determine how to measure biological aging in a spacecraft vs. remaining in Earth. This is what I am most interested in.

 

[PeterDonis]

Two twins can be measured to be of different ages, but are biological the same age, e.g. both have gray hair and aged skin.

You can't measure biological age precisely enough by things like gray hair and aged skin. People vary a lot in when, during their biological aging, they develop such features. As I've already said, we do not have any way of measuring biological aging precisely enough to directly test for differences between people who follow the kinds of paths through spacetime that we can achieve, such as astronauts spending extended periods in low Earth orbit as compared with people on Earth--or even astronauts going to the Moon or Mars as compared with people on Earth. All of the elapsed time differences in these cases, as measured by very accurate clocks, are extremely small--from a few parts per billion to at best a few parts per million. We have no way of detecting differences that small in the biological ages of people or other living things.

 

[PeterDonis]

Can you provide me with a link describing the case of the astronauts. Presumably they were able to determine how to measure biological aging in a spacecraft vs. remaining in Earth.

Did you even read my posts? I have said several times that we cannot measure biological aging that precisely.

You are now banned from this thread since you are evidently unable or unwilling to address the actual points others are making, or even read them.

 

[Ibix]

@richrf - I already showed you a way to directly link aging to clock measurements. You have a clock whose pendulum will crash into a gate and stop if the gate is closed. You open and close the gate rhythmically based on some biological process like your heartbeat, and the clock keeps running because the gate is always open just when the pendulum needs to pass. But according to relativity, any observer may consider themself to be at rest, so you, your heart, and the clock are moving at different speeds according to different observers. Thus your heart rate must slow the same amount as the clock, or else observers would disagree about direct observables like "is the clock running", "did you hear a clang from the pendulum hitting the gate".

The only way out of that is to assume that relativity is fundamentally wrong: there is some privileged frame where mechanical clocks and biological clocks tick at the same rate, but they don't in others. I'm not sure the concept really makes sense, though, since we're left wondering what two clocks that aren't synchronised but aren't wrong are even doing. How are they both clocks? And anyway, since Michelson and Morley in the 1890s we've been failing to find evidence of such a privileged frame.

Then there's the point that all macroscopic structures are made of atoms. And atoms, we do know, obey relativity (the Hafele-Keating experiment). So claiming that biological systems don't do so is a bit like the claims perpetual motion machine designers make - every component part can be shown easily to obey conservation of energy, but somehow you can combine them and they don't. Similarly, every part of a biological system is made of atoms that obey relativity, but somehow the combination doesn't. Is that at all plausible?

We have not done a twin paradox with real twins, no. We can't accelerate them to the speeds needed to see anything with a clock as imprecise as "how much grey hair do I have". But why would you expect a special exception to physics for biological systems?

 

[Mister T]

Two twins can be measured to be of different ages, but are biological the same age,

No, that's not possible, as far as I know. Do you have a reference that supports this claim?

The question is whether clock measurement observations determine the biological aging process?

Clock measurements do not determine the biological aging process, but clock readings do measure the biological aging process.

 

[PeterDonis]

All, please be aware that @richrf has been thread banned, so he cannot respond to further posts.

 

[Dale]

I need to read more to understand this. Is not clear to me why acceleration makes the differece

Acceleration, by itself, doesn’t make the difference. However, it does break the symmetry.

Relativity, like a lot of modern physics, is largely about symmetries. The principle of relativity, in particular, is talking about a symmetry between inertial reference frames.

An inertial reference frame is one where Newton’s first law (inertia) holds: an object not subject to any force moves in a straight line at a constant velocity. If you draw a spacetime diagram in such a frame, then inertial objects are represented by straight lines. There are many different inertial frames, but anything that is a straight line in one is a straight line in any other. Conversely, anything which is a bent line in one inertial frame is a bent line in any other. Bent lines in spacetime represent objects which are accelerating.

The principle of relativity asserts that all inertial frames are equally valid. That is a symmetry principle. But the traveling twin experienced acceleration so his worldline is bent in any inertial frame. But when we talk about “his frame” we specifically mean a frame where his line is straight and at rest along the t axis. So this frame cannot be inertial, and so the symmetry is broken, and his frame is not equivalent to an inertial frame.

 

[DanMP]

Everyone ages at one second per second along their own path through spacetime. The difference between the two twins is that Bob follows a shorter path through spacetime--one that has fewer total seconds along it--than Alice does. That is why Bob is younger when they meet up again.

Ok, but how Bob/Alice/any clock are physically affected by the "path through spacetime"? In the odometer analogy we know how "the path" (the road) makes the odometer to record more/less kilometers, but how does the spacetime actually affect the clocks/people?

 

[Nugatory]

Ok, but how Bob/Alice/any clock are physically affected by the "path through spacetime"? In the odometer analogy we know how "the path" (the road) makes the odometer to record more/less kilometers, but how does the spacetime actually affect the clocks/people?

Different paths through spacetime have different lengths, and the length of a timelike path through spacetime is the amount of time that a clock moving along that path ticks off. We use clocks to measure "distances" in spacetime the same way we use odometers to measure distances in space.

 

[DanMP]

Different paths through spacetime have different lengths, and the length of a timelike path through spacetime is the amount of time that a clock moving along that path ticks off. We use clocks to measure "distances" in spacetime the same way we use odometers to measure distances in space.

This is more like a definition than an explanation. It does not explain the action, if any, made by the spacetime to affect the "ticking" of the clock. For odometers we have such an action: the road makes the wheels turn/rotate due to friction. How is spacetime affecting the clocks/people?

 

[Dale]

For odometers we have such an action: the road makes the wheels turn/rotate due to friction. How is spacetime affecting the clocks/people?

For every clock we have such an action too. For an atomic clock the energy level difference for the hyperfine transition makes the oscillator oscillate at a specific frequency.

 

[phinds]

This is more like a definition than an explanation. It does not explain the action, if any, made by the spacetime to affect the "ticking" of the clock. For odometers we have such an action: the road makes the wheels turn/rotate due to friction. How is spacetime affecting the clocks/people?

Time is inherently a part of space-time and clocks measure the time part of space-time. That's all there is to it. Time is what clocks measure. All clocks tick at one second per second in their own frame of reference. There is no other "action" performed by space-time on time. What matters is, as Nugatory pointed out, the path through space-time. This is exactly analogous to a space path where distance is measured in meters instead of seconds. Don't be confused by the action of an odometer --- there are other ways to measure distance but they all measure the same distance (assuming they are working correctly).

 

[Dale]

Don't be confused by the action of an odometer --- there are other ways to measure distance but they all measure the same distance (assuming they are working correctly).

That is an excellent point. It isn’t about the odometer, it is about the geometry.

Yes, friction rolls the wheel and yes the hyperfine transition has a specific energy, but the point is that the geometry makes it so that a bent path in space always requires more wheel rotations and a bent path in spacetime requires fewer hyperfine transitions.

That is not explained by the physical mechanisms since, as you point out, we can replace them with any other mechanisms. It is explained by the geometry.

 

[PeroK]

Ok, but how Bob/Alice/any clock are physically affected by the "path through spacetime"? In the odometer analogy we know how "the path" (the road) makes the odometer to record more/less kilometers, but how does the spacetime actually affect the clocks/people?

They are fundamentally not physically affected by the travelling. It is simply that less physical time has passed.

 

[Janus]

This is more like a definition than an explanation. It does not explain the action, if any, made by the spacetime to affect the "ticking" of the clock. For odometers we have such an action: the road makes the wheels turn/rotate due to friction. How is spacetime affecting the clocks/people?

You have two men, they start off walking from the same point but in slightly different directions. They have the same stride. At some point, one of the men turns and changes the direction he is walking in so that he is now headed back towards the other man's path. Once he crosses it, bot men measure their present distance from the starting point. The man who changed direction will be shorter distance from the starting point. This was not caused by anything affecting him or the pace at which he walked, just the fact that he took a different route.
As long as you keep looking for something that "affects" the ticking of clocks as the cause for time dilation, you are barking up the wrong tree. As Dale has said, it is a geometry issue; the geometry of space-time.

 

[Orodruin]

Also, see the link in post #2 of this thread.

 

[DanMP]

For every clock we have such an action too. For an atomic clock the energy level difference for the hyperfine transition makes the oscillator oscillate at a specific frequency.

Yes, I know that, but still, where is the role of spacetime in that energy level difference and/or in the oscillation?

Time is inherently a part of space-time and clocks measure the time part of space-time.

How exactly they do that? According to Dale, clocks are counting oscillations. I can't see the direct connection between that and the spacetime, or "the time part of space-time".

Yes, friction rolls the wheel and yes the hyperfine transition has a specific energy, but the point is that the geometry makes it so that a bent path in space always requires more wheel rotations and a bent path in spacetime requires fewer hyperfine transitions.

That is not explained by the physical mechanisms since, as you point out, we can replace them with any other mechanisms. It is explained by the geometry.

The geometry is good in explaining how to understand and apply the theory, but it is as good in "explaining" what is really happening as contour lines in a topographical map: we can say that we get more tired walking between A and B because we cross contour lines (climbing a hill), but we need to explain why/how contour lines are responsible for this. The same is valid, in my opinion, for world lines / paths through spacetime: we need to show the direct connection, if there is any, between them and the clocks.

As long as you keep looking for something that "affects" the ticking of clocks as the cause for time dilation, you are barking up the wrong tree.

No, I'm pretty sure that this is "the best tree", if we want to solve the mystery of dark matter and to finally/really understand relativity.