Why was SR accepted w/o GR?

[gib65]

It occurred to me the other day that Einstein's special theory of relativity should never have been accepted unless he supplied the general theory with it. The special theory, on its own, leads to the twin paradox. You need GR to resolve this. But SR was proposed in 1905. GR was proposed and proven in 1920 - 15 years later.

 

I don't know my history that well, so maybe the answer is that SR wasn't accept until GR was proven... or maybe scientific theories are accepted regardless of whether they make sense or not so long as they pass experimental testing... or maybe physicists were desperate for something to solve the paradoxes of light that the Michelson-Morley experiment made evident.

 

Please enlighten me.

[D H]

You don't need GR to explain the twin paradox. For example, see http://en.wikipedia.org/wiki/Twin_paradox#Resolution_of_the_paradox_in_special_relativity or http://www.phys.vt.edu/~jhs/faq/twins.html. Einstein didn't even view this as a paradox. He just viewed it as an interesting consequence of special relativity.

 

Historically, special relativity was accepted rather quickly. The evidence was already in, and not just in the form of the Michelson-Morley experiment. Einstein didn't even refer to that experiment in his 1905 paper. Einstein did make extensive reference to Maxwell's equations in that paper. The main problem with special relativity was attribution rather than acceptance.

[gib65]

Thanks D H. I focused mainly on phys.vt.edu (the one that refers to Prime and Unprime), and I think I understand. It has to do with switching reference frames. When you do that, all bets are off for simultaniety.

 

What would happen in the following scenario?

 

Suppose Prime had super-human vision and was able to observe Unprime at all points in his round trip. He never travels faster than light so all light emitted by Unprime should be able to reach him and his eye receive it. What would Prime observe if he were to constantly look at Unprime?

 

I understand from the website that "Prime notices that Unprime's watch is running slowly" as he first experiences uniform velocity away from Unprime (just after accelerating). So he would at first observe Unprime to be aging more slowly as well - right?

 

I assume this is what he would observe on his return trip as well (during uniform velocity). The website also says that "Once Prime stopped at the distant station, he rejoined Unprime's frame of reference: Prime saw all the clocks in that frame to be synchronized again (but reading 1.25 years, while his own watch said 0.75 years)." So at the distant station, Prime would observe Unprime to be aging just as fast as he was (but at a younger age?).

 

What would he observe as he decelerates to the distant station? As he accelerates away from the distant station? As he decelerates at home?

 

There would have to be some point at which Prime observes Unprime leaping ahead in years to catch up to and surpass Prime in age. At what point is that?

[swansont]

There would have to be some point at which Prime observes Unprime leaping ahead in years to catch up to and surpass Prime in age. At what point is that?

 

When Unprime undergoes the acceleration.

[gib65]

When Unprime undergoes the acceleration.

 

Is that at all points of accerelation (including deceleration) or just one in particular (like when he first leaves Unprime or when he begins his return trip)?

[J.C.MacSwell]

It occurred to me the other day that Einstein's special theory of relativity should never have been accepted unless he supplied the general theory with it. The special theory, on its own, leads to the twin paradox. You need GR to resolve this. But SR was proposed in 1905. GR was proposed and proven in 1920 - 15 years later.

 

I don't know my history that well, so maybe the answer is that SR wasn't accept until GR was proven... or maybe scientific theories are accepted regardless of whether they make sense or not so long as they pass experimental testing... or maybe physicists were desperate for something to solve the paradoxes of light that the Michelson-Morley experiment made evident.

 

Please enlighten me.

 

Einstein was given the Nobel Prize in 1921 for his work in theoretical Physics, especially for his description of the photoelectrical effect, but at that time they intentionally chose to avoid mentioning his work on relativity (SR or GR). At that time I think it was still controversial.

[NowThatWeKnow]

Is that at all points of accerelation (including deceleration) or just one in particular (like when he first leaves Unprime or when he begins his return trip)?

 

During acceleration away from Earths frame your clock will continue to run slower and slower as you accelerate. When you shut off your engines and become an inertial frame moving away from Earth your clock will maintain a ratio of running slow. As you decelerate back to Earth's frame your clocks will speed up until they match the speed of Earth's clocks. The same thing happens on the way home.

 

Does that sound right Swansont?

[swansont]

Is that at all points of accerelation (including deceleration) or just one in particular (like when he first leaves Unprime or when he begins his return trip)?

 

All acceleration. (In physics, "deceleration" is a subset of acceleration, rather than being its opposite)

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Merged post follows:

Consecutive posts merged

During acceleration away from Earths frame your clock will continue to run slower and slower as you accelerate. When you shut off your engines and become an inertial frame moving away from Earth your clock will maintain a ratio of running slow. As you decelerate back to Earth's frame your clocks will speed up until they match the speed of Earth's clocks. The same thing happens on the way home.

 

Does that sound right Swansont?

 

Yes.

 

The standard twins paradox has the moving twin already at constant velocity when the clocks are synchronized, so it avoids the issue of that initial acceleration.

[gib65]

During acceleration away from Earths frame your clock will continue to run slower and slower as you accelerate. When you shut off your engines and become an inertial frame moving away from Earth your clock will maintain a ratio of running slow. As you decelerate back to Earth's frame your clocks will speed up until they match the speed of Earth's clocks. The same thing happens on the way home.

 

 

That would be true from the point of view of the stay-at-home twin. But relativity says that from the your point of view, the stay-at-home twin is moving. So from your point of view, the stay-at-home twin's clock will appear to run slower.

[NowThatWeKnow]

That would be true from the point of view of the stay-at-home twin. But relativity says that from the your point of view, the stay-at-home twin is moving. So from your point of view, the stay-at-home twin's clock will appear to run slower.

 

I never understood why they confused the twin paradox with "the way it appears" to each twin. At least until you go through it in real time using local clocks. The reality of the relativity is the stay at home twins clock (due to no acceleration) is going much faster then the traveling twin. That is apparent when you compare the ages when they reunite. The way it appears to each twin because of relativistic speeds should be covered in part two IMO.

[Bob_for_short]

Einstein was given the Nobel Prize in 1921 for his work in theoretical Physics, especially for his description of the photoelectrical effect, but at that time they intentionally chose to avoid mentioning his work on relativity (SR or GR). At that time I think it was still controversial.

 

No, SR was not controversial. The problem was in H. Loretnz who knew the works of H. Poincaré on Poincaré's principle of relativity and relativistic mechanics. H. Poincaré in turn considered his own contribution modestly and attributed the main achievements to H. Lorentz. H. Poincaré had written many scientific and popular articles on this subject, and A. Einstein studied them. But A. Einstein never mentioned the works of the academician H. Poincaré and tried not to mention the Lorentz transformations. He popularized the principle of relativity with playing with clocks and rods but he never dealt with real conceptual problems, for example, with radiative friction in relativistic mechanics. His achievements were not so personal. With H. Lorentz alive at that time, it was not possible to give the Nobel prize to A. Einstein for SR.

GR was developed also with help of H. Minkowski, M. Grossmann, and D. Hilbert (the latter was still alive).

 

Bob.

Edited May 5, 2009 by Bob_for_short

[gib65]

I never understood why they confused the twin paradox with "the way it appears" to each twin. At least until you go through it in real time using local clocks. The reality of the relativity is the stay at home twins clock (due to no acceleration) is going much faster then the traveling twin. That is apparent when you compare the ages when they reunite. The way it appears to each twin because of relativistic speeds should be covered in part two IMO.

 

Well, if you really want to get to the bottom of relativity, neither of the twins' clocks are going faster or slower than the other in any absolute sense, at least not when they are travelling at uniform velocity. Acceleration may be another matter. One of the first insights that lead Einstein to SR was the relativity (or non-existence?) of simultaneity. That is to say whether two events happen simultaniously or not depends on the observer and his speed relative to those events.

 

So whether the one twin's clock strikes 1:00 simultaniously as the other's strikes 2:00 or visa-versa is not an absolute fact. It can legitimately be said that relative to one, 1:00 happens before 2:00 but relative to the other, 2:00 happens before 1:00.

 

When the travelling twin turns around, he accelerates, and that constitutes a shifting in reference frames, which allows for any adjustment needed to compensate for the discordance between their temperals schisms.

[NowThatWeKnow]

Well, if you really want to get to the bottom of relativity, neither of the twins' clocks are going faster or slower than the other in any absolute sense, at least not when they are travelling at uniform velocity. Acceleration may be another matter. One of the first insights that lead Einstein to SR was the relativity (or non-existence?) of simultaneity. That is to say whether two events happen simultaniously or not depends on the observer and his speed relative to those events.

 

So whether the one twin's clock strikes 1:00 simultaniously as the other's strikes 2:00 or visa-versa is not an absolute fact. It can legitimately be said that relative to one, 1:00 happens before 2:00 but relative to the other, 2:00 happens before 1:00.

 

When the travelling twin turns around, he accelerates, and that constitutes a shifting in reference frames, which allows for any adjustment needed to compensate for the discordance between their temperals schisms.

 

It sounds like you are complicating things combining what is observed and what is really happening and worrying about simultaneous events when it isn't necessary. That is what I was saying is a problem to me with most twin paradox examples. Sort of like mixing frames and getting all screwed up.

 

You mentioned "when they are travelling at uniform velocity" which I take as they are at rest with each other and in the same frame as far as SR goes.

 

I think post #7 put it well (swansont approved) but this is what I understand.

If the Earth twin and the traveling twin both had a universal clock synchronized at rest with the CMB with them, the Earth twin would see a consistent minute difference between his local and universal clock. This is because Earth is not totally at rest with the CMB.

 

The traveling twin would notice during acceleration out of Earth's frame that his proper time clock would start running slower and slower then the universal clock. When the engines were shut off and he becomes an inertial frame, the proper time clock would run consistently slower then the universal clock. When the traveling twin turned around and accelerated (decelerate) towards Earth's frame his proper time clock would eventually become synchronized with the universal clock. As he accelerates towards Earth the whole thing starts over.

 

Martin, swansont, do you see any flaws? I very much consider myself a layman and get corrected often.

Edited May 6, 2009 by NowThatWeKnow

[swansont]

The traveling twin would notice during acceleration out of Earth's frame that his proper time clock would start running slower and slower then the universal clock. When the engines were shut off and he becomes an inertial frame, the proper time clock would run consistently slower then the universal clock. When the traveling twin turned around and accelerated (decelerate) towards Earth's frame his proper time clock would eventually become synchronized with the universal clock. As he accelerates towards Earth the whole thing starts over.

 

Not synchronized — the clock will be behind the Master clock. (I prefer that term to universal) It will run at the same rate when it's in the same inertial frame, which means it is syntonized, but it will not read the same number. Synchronized means same rate and same reading, i.e. synchronized ideal clocks remain synchronized if unperturbed.

[NowThatWeKnow]

Not synchronized — the clock will be behind the Master clock. (I prefer that term to universal) It will run at the same rate when it's in the same inertial frame, which means it is syntonized, but it will not read the same number. Synchronized means same rate and same reading, i.e. synchronized ideal clocks remain synchronized if unperturbed.

Correction accepted, synchronized was the wrong word. It would be running at the same speed but behind the master clock when they shared the same inertial frame mid way. Thanks for keeping an eye on me.

[gib65]

It sounds like you are complicating things combining what is observed and what is really happening and worrying about simultaneous events when it isn't necessary. That is what I was saying is a problem to me with most twin paradox examples. Sort of like mixing frames and getting all screwed up.

 

I'm not complicating anything. That's just the way the theory is.

 

You mentioned "when they are travelling at uniform velocity" which I take as they are at rest with each other and in the same frame as far as SR goes.

 

No, it just means neither one is accelerating. They could be going a different speeds though.

 

Here's some good videos that explain SR:

 

<-- simultaniety

 

<-- time dilation

 

The last minute and a half of the last video (starting at 7:30) stresses my point, but you should watch the whole thing because it's all relevant to understanding SR.

[NowThatWeKnow]

I'm not complicating anything. That's just the way the theory is.

 

No, it just means neither one is accelerating. They could be going a different speeds though...

 

You were asking questions that indicated the combination of information presented in the twin paradox was confusing you. I tried to break it down twice in a way for you grasp where and when the time differences actually took place and not where and when it appeared to take place from different frames. If my simple version did not make sense to you then I am not sure how else to put it. It seems the powers that be had no problem with my version. Good luck on a complete understanding as it is not intuitive.

 

"travelling at uniform velocity". Uniform relative to what? Each other? The CMB? The Earth? You lost me.

[gib65]

You were asking questions that indicated the combination of information presented in the twin paradox was confusing you.

 

When did I ask this? I began this thread asking why SR was accepted without GR. Since then, I got my answer.

 

I also asked a question about what the travelling twin would see if he constantly looked at his stay-at-home brother. I got my answer to that as well.

 

My reply to your comment was simply to add something I felt was important for a full understanding of relativity.

 

I tried to break it down twice in a way for you grasp where and when the time differences actually took place and not where and when it appeared[/b'] to take place from different frames.

 

Dude, there is no 'actual'. That's the whole point of relativity. There are only relative states. The travelling twin isn't 'actually' travelling while the stay-at-home only 'appears' to be travelling from the point of view of the travelling twin. Both are actually travelling relative to the other. Einstein didn't just pull the term 'relativity' out of thin air.

 

If my simple version did not make sense to you then I am not sure how else to put it.

 

You're version's a little too simple. Did you even watch the videos I offered?

 

It seems the powers that be had no problem with my version.

 

That's because there was nothing wrong with your version. It was just incomplete.

 

Good luck on a complete understanding as it is not intuitive.

 

Actually, I find it quite intuitive. Good luck to you (you'll need a lot of it).

 

"travelling at uniform velocity". Uniform relative to what? Each other? The CMB? The Earth? You lost me.

 

Yes, each other.

[NowThatWeKnow]

When did I ask this?

I saw confusion in post #3:

"What would Prime observe if he were to constantly look at Unprime?"

"So he would at first observe Unprime to be aging more slowly as well - right?"

"So at the distant station, Prime would observe Unprime to be aging just as fast as he was (but at a younger age?)."

"What would he observe as he decelerates to the distant station? As he accelerates away from the distant station? As he decelerates at home?"

"There would have to be some point at which Prime observes Unprime leaping ahead in years to catch up to and surpass Prime in age. At what point is that?"

I saw confusion in post #5

"Is that at all points of accerelation (including deceleration) or just one in particular (like when he first leaves Unprime or when he begins his return trip)?"

 

That is when I chimed in. I have seen almost everyone (including myself) have trouble with the twin paradox. I finally figured out that you could look at it in steps and it was easier to understand. You must learn to add and subtract before moving onto algebra. My simple version is NOT complete when it comes SR, but it lets you understand addition before moving on.

 

My reply to your comment was simply to add something I felt was important for a full understanding of relativity.

Again, I need the basics, one step at a time, to even understand some of relativity. Then I will move onward.

 

Dude, there is no 'actual'. That's the whole point of relativity. ...

 

I basically understand relativity of simultaneity but that does not make my story invalid. While the twins speeds are not uniform to each other there is an 'actual' and continuous difference occurring in there proper times. This is why having a master clock set to Earth time shows when and where the traveling twins 'actual' changes take place. When you understand this, the second part makes much much much more sense (at least to me).

 

You're version's a little too simple. Did you even watch the videos I offered?

I consider myself a beginner and I need simple to grasp things that are not intuitive.

 

I watched both videos and thought the second one was especially well done. I have watched similar videos in the past trying to grasp relativity at a basic level.

 

 

That's because there was nothing wrong with your version. It was just incomplete.

We all crawl before walking.

 

I am far from an expert and do not want to get into a P!$$!ng match with anyone. I just try to add my input when I think it may be food for thought. From reading your post I see you are ahead of me in many areas and I am trying to catch up. I did see one area where I could add a view from a different angle to help grasp the difficult concepts of SR. I did not mean to offend anyone and hope we can all be friends and learn from each other.

[gib65]

Fair enough. And I'm sorry on my part for being snippy.

 

I think we misinterpreted each other. I was adding something further to your comment and I think you interpreted that for a search for further answers (as though your comment didn't make sense).

 

I basically understand relativity of simultaneity but that does not make my story invalid.

 

Your story is not invalid in the sense that you can posit that a Master Clock exists relative to which all other clocks' date=' insofar as they are moving relative to it, slow down. But this is only in virtue of choosing a reference frame in which the Master Clock is fixed. If we were to choose our reference frame such that the stay-at-home twin was fixed, then the Master Clock would be moving relative to it and tick slower. If we chose to consider the travelling-twin as fixed, both the Master Clock and the stay-at-home twin's clock would be running slower.

 

Those who are just getting into relativity often have a hard time with accepting that there is no answer to the question "Okay, but really - who's [i']actually[/i] moving? Whose clock is really ticking slower?" The answer is, it depends.

 

This can be difficult to grasp unless you get the principle of the relativity of simultaniety. According to that principle, it's certainly possible that in one reference frame, as one person's clock (who's fixed) approaches 2:00, a second person's clock (who's moving) approaches 1:00, and they both strike those hours simultaniously, but in a different reference frame, it's the exact opposite. The first person's clock (who's now considered moving) approaches 1:00 whereas the other's (who's now considered fixed) approach 2:00, and they both strike those hours simultaniously.

 

If you can wrap your head around that concept, the rest of relativity is a breeze (as far as I'm concerned).

[swansont]

Those who are just getting into relativity often have a hard time with accepting that there is no answer to the question "Okay, but really - who's actually moving? Whose clock is really ticking slower?" The answer is, it depends.

 

Or, as I have said on occasion, saying that something is moving without giving a reference is equivalent to asking, "What's the difference between a duck?"

[NowThatWeKnow]

...Your story is not invalid in the sense that you can posit that a Master Clock exists relative to which all other clocks, insofar as they are moving relative to it, slow down. But this is only in virtue of choosing a reference frame in which the Master Clock is fixed. If we were to choose our reference frame such that the stay-at-home twin was fixed, then the Master Clock would be moving relative to it and tick slower. If we chose to consider the travelling-twin as fixed, both the Master Clock and the stay-at-home twin's clock would be running slower...

 

For some reason I am not clear on what you are saying above. Let me put it a different way and you let me know if we agree. To keep it simple, both twins start off on Earth and both have master clocks that stay synchronized to each other.

 

Example #1:

The master clocks are synchronized to Earth time and the twin blast off. Earths master time and proper time remain synchronized. The traveling twins proper time starts slowing down relative to master time. The Earth twin starts aging faster then the traveling twin.

 

Example #2:

the master clocks are synchronized to the traveling twins proper time and the twin blast off. Now the traveling twins proper time stays synchronized to the master clocks and the Earths proper time starts speeding up relative to the master clock. Again we can see the earth twin aging faster.

 

Do we agree?

It seems that acceleration is the key. Starting off with both twins moving makes my head hurt. Maybe a good exercise, but not good for me, the beginner, trying to grasp the basics.

[gib65]

Or, as I have said on occasion, saying that something is moving without giving a reference is equivalent to asking, "What's the difference between a duck?"

 

Ha! Or like I've said: "My car goes 300km!!!" as an expression of its speed.

 

For some reason I am not clear on what you are saying above. Let me put it a different way and you let me know if we agree. To keep it simple' date=' both twins start off on Earth and both have master clocks that stay synchronized to each other.

 

Example #1:

The master clocks are synchronized to Earth time and the twin blast off. Earths master time and proper time remain synchronized. The traveling twins proper time starts slowing down relative to master time. The Earth twin starts aging faster then the traveling twin.

 

Example #2:

the master clocks are synchronized to the traveling twins proper time and the twin blast off. Now the traveling twins proper time stays synchronized to the master clocks and the Earths proper time starts speeding up relative to the master clock. Again we can see the earth twin aging faster.

 

Do we agree?

It seems that acceleration is the key. Starting off with both twins moving makes my head hurt. Maybe a good exercise, but not good for me, the beginner, trying to grasp the basics.

[/quote']

 

Generally yes, we agree - for acceleration.

 

I would point out, however, that a Master Clock is a clock that is not moving. So they can't both have a Master Clock, but they can both synchronize their clocks to the Master at the start - but only one of them will stay synchronized to it, and which one that is depends on whether the Master Clock stays at home or goes along for the ride.

[NowThatWeKnow]

I would point out, however, that a Master Clock is a clock that is not moving. So they can't both have a Master Clock,...

But I think they both could have a master clock (or call it what you want) that is synchronized with each other. The clocks on the GPS satellites are a good example of clocks adjusted for both GR and SR so they are synchronized with earth clocks. Future technology will allow the clocks to maintain synchronization during acceleration. At this point I can use my mind to imagine any technology necessary to help me understand relativity.

[D H]

I would point out, however, that a Master Clock is a clock that is not moving.

Not moving with respect to what? Keep in mind that there is no such thing as an absolute reference frame.