Correct phrasing / use of vocabulary for SR

[PeterDonis]

Scrap all those ambiguous words. Easy cake. Talk about simultaneity, not the 'sense' of simultaneity. Moving trains are shorter, not 'appear' shorter, and definitely not 'seems' to get shorter (for reasons explained in my post).

I see the advantages of this approach, but you still have to be careful not to draw unwarranted deductions from it. As with:

Face what Einstein found out and accept the consequences: block universe, even if you feel uncomfortable with the consequences (such as free will).

And as I and others have argued in a number of threads by now, SR does *not* imply hard determinism! So if the language you suggest is going to make people believe that it does, then that, IMO, is a big disadvantage in your proposal.

I know that most people refuse to take that step.

Because it's not logically justified. SR is *consistent* with hard determinism, but it does not *require* hard determinism.

Perhaps it's worth expanding on this. SR, if we consider it as an exact theory, is *wrong*. Spacetime is not globally flat; it's curved. SR is an *approximate* theory that works OK in cases where spacetime curvature can be neglected. There are many such cases.

GR is a more comprehensive theory which includes SR as a special case; and one could argue that GR, if it were an exact theory, would imply hard determinism. But GR includes something crucial that SR does not: dynamics. SR, in itself, has no dynamics; it's all kinematics. You have to *add* some dynamics to SR for it to actually make physical predictions. GR, all by itself, can give you dynamics in any case where gravity is the only significant factor involved. Again, there are many such cases. So even if GR would imply hard determinism if it were exactly right, SR can't, because hard determinism is a claim about dynamics, not just kinematics.

But GR, as an exact theory, is also wrong; it predicts infinite spacetime curvature in certain cases, such as the r = 0 singularity of a black hole or the initial singularity in an FRW spacetime. Infinite spacetime curvature is not physically reasonable, so GR as a theory can't be exactly right. So even if GR would imply hard determinism if it were exactly right, that's irrelevant, because it's not.

 

[bobc2]

NO.
"Physics is an apptemt conceptually to grasp reality as it is thought, independently of its being observed. In this sense, one speaks of physical reality." --Einstein
Einstein looked further than the observations. (And he knew there's more to physics than mathematics.)

Great quote, Vandam. And it is so very relevant for this kind of discussion. Thanks.

 

[Dale]

These calculated effects are not optical so the word "appear" is not appropriate. But how can something that is not optical be an optical illusion?

You are, of course, correct. It is an absurd impression, but nonetheless it is one that many new students get. They often think that time dilation and relativity of simultaneity are optical illusions, perhaps due to things like photon clocks and typical thought experiments. Using words like "appear" makes overcoming that just a little more challenging.

I don't see how "appear" versus "seem" resolves this issue. It's always going to take phrases and extra commentary to clarify what we mean. [Notice how I just used the word "see" in a non-optical sense.]

I agree that "seem" doesn't provide any benefit over "see".

 

[ModusPwnd]

Be careful with 'observed'. Optical illusions are observations but you know they are not valid observations.

Of course optical illusions are valid observations. It the conclusions you draw from them that may be invalid. If you observe a pool of water on hot asphalt or observe a car wheel running backwards those are valid observations. If you conclude that you could go drink that water or the car wheel is fighting the motion of the car, then those conclusions would be invalid (since they don't jive with other observations).

Sorry for the digression...

 

[Vandam]

Peter, to dicsuss SR/free will with you will take ages. And off topic here. And I'm also afraid a discussion about free will be considered far too philosophical. Even in the context of SR. I gave my short point of view on this, I know yours, I prefer to keep it that way if you don't mind.

 

[Dale]

Then stop bringing it up.

 

[Vandam]

Of course optical illusions are valid observations. It the conclusions you draw from them that may be invalid. If you observe a pool of water on hot asphalt or observe a car wheel running backwards those are valid observations. If you conclude that you could go drink that water or the car wheel is fighting the motion of the car, then those conclusions would be invalid (since they don't jive with other observations).

Sorry for the digression...

Correct. Sorry about that.

So if simultaneous events are observed as non-simultaneous in another frame let's not make the wrong conclusions. The are non-simultaneus, not only observed as non-simultaneous.

 

[ModusPwnd]

I agree (but I don't think the distinction is relevant). Thats what I was taught when I was in school and that's what the theory and observations each imply.

Cant blame students for being skeptical though! Intuition is a hard nut to crack.

 

[Vandam]

Then stop bringing it up.

It the first time ever I bring this free will thing in my post.
So after this one-off I will indeed stop to please you.

But I will not stop bringing up the block universe in this forum. No way.

 

[ghwellsjr]

So if simultaneous events are observed as non-simultaneous in another frame let's not make the wrong conclusions. The are non-simultaneus, not only observed as non-simultaneous.

You just agreed with me that relativity of simultaneity is not observerable:

Please don't take me out of context. I was specifically referring to the calculated effects that DaleSpam just mentioned:

When I am talking about calculated effects, such as length contraction or time dilation or relativity of simultaneity, then I think that the word appear conveys the connotation that SR effects are optical illusions.

These effects are not "a matter of observation of measurement instruments". An observer cannot optically observe these effects either with his naked eyes or with the help of instruments because they are always, because they involve moving objects, remote observations and we have to factor out the time delay caused by the propagation of light which always involves an arbitrary assumption about how long that takes and then a calculation. You need a well-defined frame with coordinates to discuss those three non-optical effects.

I agree.

Why then are you now talking about observing the simultaneity or non-simultaneity of events? What you should be saying is that events in one frame are simultaneous and not simultaneous in another frame. Forget about observing, or seeing, or viewing, or appearing.

 

[ModusPwnd]

What you should be saying is that events in one frame are simultaneous and not simultaneous in another frame. Forget about observing, or seeing, or viewing, or appearing.

I don't see the difference between those. All we can do is observe and all scientific theories can do is predict and describe our observations. You seem to be appealing to some kind of presumed underlying 'reality' which is not relevant here, or anywhere in science.

 

[PeterDonis]

It the first time ever I bring this free will thing in my post.

It's the first time you've specifically mentioned the term "free will", AFAIK. And I agree that a discussion of free will is way off topic for this thread and this forum.

But it is not the first time you have claimed that SR requires hard determinism. And that is really what I am disputing.

But I will not stop bringing up the block universe in this forum. No way.

And I will keep challenging you to prove that SR requires hard determinism, given the issues I raised in my earlier post. As long as you are unable to prove that, I will continue to point that out.

 

[ghwellsjr]

What you should be saying is that events in one frame are simultaneous and not simultaneous in another frame. Forget about observing, or seeing, or viewing, or appearing.

I don't see the difference between those. All we can do is observe and all scientific theories can do is predict and describe our observations. You seem to be appealing to some kind of presumed underlying 'reality' which is not relevant here, or anywhere in science.

Well let's talk about when the rover recently landed on Mars. Since it took 14 minutes in the solar system rest frame for the signal to get from Mars to Earth, everyone knew that when we received the signal that the parachute had opened and the seven minutes of terror had already begun, the rover actually was already on the surface of Mars, either sending out good signals or a $2.5 billion piece of trash. The event of the landing on Mars was simultaneous with the event of the commentators on Earth saying that the seven minutes of terror was still seven minutes away. In fact, I think they even pointed out that the landing had already occurred but what would everyone think if they said "we now observe the rover landing on Mars"?

 

[ModusPwnd]

That looks like a simple confusion between signal propagation time and time dilation. Thats not really what is at issue here, is it?

We observe the signal that the craft has landed, we observe the speed of signal propagation and infer when it landed (w.r.t. our frame of course).
A different planet in a different frame would observe the signal, observe the speed of signal propagation and infer when it landed (w.r.t. its own frame).

 

[ghwellsjr]

That looks like a simple confusion between signal propagation time and time dilation. Thats not really what is at issue here, is it?

Huh? There's no time dilation involved here, why do you say that? I'm not confused about what I said but I am confused about what you said.

We observe the signal that the craft has landed, we observe the speed of signal propagation and infer when it landed (w.r.t. our frame of course).
A different planet in a different frame would observe the signal, observe the speed of signal propagation and infer when it landed (w.r.t. its own frame).

As I said, in the solar system rest frame, we observe the signal 14 minutes after it happened but we don't observe the landing event simultaneously with the event happening. That's the issue. Is it appropriate to talk about observing remote events when the signals of those events haven't reached us yet?

We don't have to be on a different planet to describe the same events in a different frame. We can take a frame that is moving at just a hair under the speed of light in the direction from Mars to Earth. Then we can say that the landing happened just milliseconds prior to our observing it.

 

[ModusPwnd]

What I mean is that time dilation implies the relativity of simultaneity (or vise versa), not finite transmission speeds.

The fact that it takes light 14 minutes to reach us does not imply the relativity of simultaneity.

I see no problem in taking for granted that any observer is able to back calculate events based on the finite propagation of signals.

We can take a frame that is moving at just a hair under the speed of light in the direction from Mars to Earth.

It doesn't really matter which way we are traveling. Time dilation and the relativity of simultaneity does not depend on velocity, it depends on speed.

 

[Austin0]

What I mean is that time dilation implies the relativity of simultaneity (or vise versa), not finite transmission speeds.

The fact that it takes light 14 minutes to reach us does not imply the relativity of simultaneity.

I see no problem in taking for granted that any observer is able to back calculate events based on the finite propagation of signals.




It doesn't really matter which way we are traveling. Time dilation and the relativity of simultaneity does not depend on velocity, it depends on speed.

The relativity of simultaneity depends on velocity. I.e. it is direction dependent

 

[Vandam]

You just agreed with me that relativity of simultaneity is not observerable:

?

If I said that if simultaneous events are observed as non-simultaneous in another frame, I mean that in that other frame they are not only 'observed' as non-simultaneous, but also 'are' non-simultaneous in that frame.

Why then are you now talking about observing the simultaneity or non-simultaneity of events? What you should be saying is that events in one frame are simultaneous and not simultaneous in another frame. Forget about observing, or seeing, or viewing, or appearing.

That's what I meant.

 

[Vandam]

It's the first time you've specifically mentioned the term "free will", AFAIK. And I agree that a discussion of free will is way off topic for this thread and this forum.

But it is not the first time you have claimed that SR requires hard determinism. And that is really what I am disputing.



And I will keep challenging you to prove that SR requires hard determinism, given the issues I raised in my earlier post. As long as you are unable to prove that, I will continue to point that out.

Peter, we went through such a discussion. I stopped the discussion because everythinhg you wrote didn't make sense to me. My conclusion was that you only believe in the existence of your own present event, nothing else. See also https://www.physicsforums.com/showpost.php?p=3990686&postcount=89.
And I leave it there.

 

[ghwellsjr]

What I mean is that time dilation implies the relativity of simultaneity (or vise versa), not finite transmission speeds.

Time dilation is what happens to moving objects (clocks) in a single frame. Relativity of simultaneity refers to the fact that pairs of events have different time differences in different frames.

The fact that it takes light 14 minutes to reach us does not imply the relativity of simultaneity.

The difference in the times of the events where the light leaves Mars and arrives at Earth is frame dependent. In the solar system rest frame it is 14 minutes. In other frames, it takes on other values. See below.

I see no problem in taking for granted that any observer is able to back calculate events based on the finite propagation of signals.

Of course, but don't you see the problem with someone saying that an observer can observe events simultaneously with their occurrence? In other words, the observer's rest frame permits him to assign the same coordinate time to distant events that he sees on his local clock and this leads some people to think that also permits him to observe those distant events simultaneously with their occurrence not later as you describe. The term "relativity of simultaneity" applies to the fact the coordinate times of remote events is not absolute but dependent on the chosen frame, just like time dilation and length contraction.

We can take a frame that is moving at just a hair under the speed of light in the direction from Mars to Earth.

It doesn't really matter which way we are traveling. Time dilation and the relativity of simultaneity does not depend on velocity, it depends on speed.

You're right that time dilation depends only on speed within a chosen frame but we're not talking about time dilation. We're talking about viewing remote events. And direction does make a difference when considering different frames. You should work this out. In a frame traveling at 0.9999c in the direction from Mars to Earth, an event on Mars takes less than 10 milliseconds for us to observe it on Earth. In a frame traveling at the same speed in the opposite direction it takes almost five and a half hours.

 

[ModusPwnd]

Well, its clear that I don't know enough to see the distinction you are making. Its been a few years since I have looked at this stuff and I never was that good back then either.

In other words, the observer's rest frame permits him to assign the same coordinate time to distant events that he sees on his local clock and this leads some people to think that also permits him to observe those distant events simultaneously with their occurrence not later as you describe. The term "relativity of simultaneity" applies to the fact the coordinate times of remote events is not absolute but dependent on the chosen frame, just like time dilation and length contraction.

I honestly didnt think anybody was confused about that in the bold. At least, not in this thread. Saying two things happen simultaneously, in my mind, means that after I have collected the signals I calculate that they happened at the same time coordinate, in my frame. You can never observe an event when it happens, unless your observation is the 'event'...

 

[Vandam]

It's not because you have not observed an event that it doesn't or didn't exist yet.
When the signal has not arrived yet, the rover has already landed safely on Mars or crashed. Whether it has landed safely or not is already a real fact before you observe it.

<<Physics is an attempt conceptually to grasp reality as it is thought, independently of its being observed. In this sense, one speaks of physical reality>>quote Einstein.

Einstein looked further than the observations. Quite a few people here do not want to look further than observations. Einstein would not share that kind of approach.

 

[ModusPwnd]

Einstein looked further than the observations. Quite a few people here do not want to look further than observations. Einstein would not share that kind of approach.

You can count me as one of those people. And lacking Einstein's approval honestly does not bother me at all.

Observations can be predicted and described, in qualitative or quantitative ways. "Reality" doesn't really matter. You can postulate any type of underlying reality you like. But if that postulate does not increase our predicative or descriptive power then it is superfluous to the theory. If it does increase our power, then its incorporation into the theory is because of observations and observations alone (observations that the postulate increases predictive ability).

Didn't Einstein also say something about not making any theory more complicated than needed? Isn't presuming an underlying reality with no benifit to the theory doing just that?

 

[Vandam]

You can count me as one of those people. And lacking Einstein's approval honestly does not bother me at all.

Observations can be predicted and described, in qualitative or quantitative ways. "Reality" doesn't really matter. You can postulate any type of underlying reality you like. But if that postulate does not increase our predicative or descriptive power then it is superfluous to the theory. If it does increase our power, then its incorporation into the theory is because of observations and observations alone (observations that the postulate increases predictive ability).

Didn't Einstein also say something about not making any theory more complicated than needed? Isn't presuming an underlying reality with no benifit to the theory doing just that?

Well, reality doesn't matter to you.
If I see a tree in front of me I have a concept of a tree that was there/is there independent of observations. You and many others on this forum reject this because you find this philosophical mumbo jumbo. I'm not a solipsist.

 

[ModusPwnd]

Well, reality doesn't matter to you.

I don't think it matters with respect to science. Outside of science I can conject and hypothesize away.

If I see a tree in front of me I have a concept of a tree that was there/is there independent of observations.

Aww, that's not true man. That like saying a blind mans knows what red looks like. If you never had an observation of a tree how would you create that concept to begin with? Its the collection of many observations you have made over your life that forms the concept of your tree.

You and many others on this forum reject this because you find this philosophical mumbo jumbo.

I reject because I don't see it adding any predictive or descriptive power to our theories. In that sense it is completely superfluous and thus irrelevant to science. It may be relevant to other philosophical areas, but not 'natural' philosophy, not science.

I'm not a solipsist.

A key tenant of science, IMO and I think many others as well, is that all theories are tentative with respect to new observations. All of them. Presuming that any are immune to new counter observations is denying any further investigation. That is counter to science. This is not nearly as hard of a line as I think of a solipsist as taking. But if it is, so be it. We are talking science here - not philosophy at large.

 

[ghwellsjr]

In other words, the observer's rest frame permits him to assign the same coordinate time to distant events that he sees on his local clock and this leads some people to think that also permits him to observe those distant events simultaneously with their occurrence not later as you describe. The term "relativity of simultaneity" applies to the fact the coordinate times of remote events is not absolute but dependent on the chosen frame, just like time dilation and length contraction.

I honestly didnt think anybody was confused about that in the bold. At least, not in this thread. Saying two things happen simultaneously, in my mind, means that after I have collected the signals I calculate that they happened at the same time coordinate, in my frame. You can never observe an event when it happens, unless your observation is the 'event'...

Maybe not in this thread, but haven't you seen many cases of people insisting that it's important for an observer to have a perspective or a point of view from his own rest frame, even he's not inertial?

 

[Vandam]

I don't think it matters with respect to science. Outside of science I can conject and hypothesize away.

Aww, that's not true man. That like saying a blind mans knows what red looks like. If you never had an observation of a tree how would you create that concept to begin with? Its the collection of many observations you have made over your life that forms the concept of your tree.

I reject because I don't see it adding any predictive or descriptive power to our theories. In that sense it is completely superfluous and thus irrelevant to science. It may be relevant to other philosophical areas, but not 'natural' philosophy, not science.
A key tenant of science, IMO and I think many others as well, is that all theories are tentative with respect to new observations. All of them. Presuming that any are immune to new counter observations is denying any further investigation. That is counter to science. This is not nearly as hard of a line as I think of a solipsist as taking. But if it is, so be it. We are talking science here - not philosophy at large.

I'm not saying observations are not important.
I'm saying that based on the observations we know what the exteriour world is made of independent of observations: I see a tree because there was a tree even before it was observed.

In a frame two events are observed simultaneous because they are simultaneous in that framle even if not observed. And those two events are non-simultaneous in another frame because they are non-simultaneous in that frame, even not observed. That's SR and block unverse. For me Block universe is the only correct physical interpretation of SR. All the rest I consider philosophical ad hoc explanations. Of course you do not agree with what I say.

 

[Dale]

I'm not a solipsist.

Nor are most of the people who disagree with you on some of your more extreme block universe positions.

 

[bobc2]

Nor are most of the people who disagree with you on some of your more extreme block universe positions.

"...extreme block universe positions"? I've seen nothing extreme about the positions presented by Vandam. Block universe is widely discussed among physicists--quite a few references have been cited on this forum. LET is usually the concept offered as proof that block universe is not the only world view among physicists. I personally have not dug into the details sufficiently to critique LET.

My grad school prof discussed it only briefly and basically dismissed it as an alternative to the Einstein-Minkowski 4-dimensional universe. So, I took on that same attitude without really doing my own homework on the subject. I've always assumed that LET did not have the natural connection to general relativity that is had by special relativity. The little homework I did with LET years ago left me feeling that one would have to deal in tedious detail with many different special relativity effects and examples before considering LET a valid theory. Contrast that with the ease that the 4-dimensional universe concept clarifies so many different special cases of phenomena related to special relativity.

 

[Vandam]

Nor are most of the people who disagree with you on some of your more extreme block universe positions.

Extreme block positions...
At least I have a position. After all the posts I've read of the non block followers (like you) I still do not understand a word. Even if you try to explain it.
Or there are a lot of solipsists on this forum. Or you all believe in LET, I.e. mathematical illusions to save the physical ether. And probably a combination of both.
Or what else is it?
That all has nothing to do with SR. Solipsism is for philosophy forum. And LET is an ether disaster and old school (Lorentz himself admitted it). So in fact both approaches are off topic on this SR forum.