# Are relativistic effects real ?

Hello stillwonder.

An object is moving inertially or not moving inertially. Clocks do not define this. The clocks of course will only remain synchronized if they are in zero relative motion to each other.

Matheinste

Janus
Staff Emeritus
Gold Member
Let me point out that following calculations are made in rest frame of O.
1. The distance beween the posts '||' = d
2. The velocity v of the spaceships S
Hence the time needed to cross distance d is d/v. These can be computed to arbitrary precision.
3. S's clock is stopped when it reaches '|'. This can be automated via having S fly arbitrarily close to post '|'. Infact, O can actually observe this himself that S stops the clock when he reaches the post '|'.

Assertions:

1. O's clock shows d/v
2. If there is time dilation, S's clock must show less than d/v
3. If there is no time dilation, S's clock also shows d/v

There is no option of S stopping his clock after crossing the post, since he would have crashed into mountain range M (not shown).

So, will the clocks read same value or not?

The choice for O is :
1. Are his scientific calculations wrong?
2. Is his "eyeball" observation of time dilation misleading because of delays in receiving signals from far.
S does not reach his post at the same time as O reaches his post according to O, S's clock does stop when it reaches the post, but reaches his post after O reaches his post.

You have to take the relativistic addition of velocities into account.

$$w=\frac{u+v}{1+\frac{uv}{c^2}}$$

where v is the velocity of O and u is the velocity of S and w is the velocity of S to O as measured by O.

Thus O sees sees the time for himself to travel distance d as d/v, but the time it takes S to traverse distance d is$$\frac{d}{ \frac{u+v}{1+\frac{uv}{c^2}}-v}$$

Also, from your set up, O and S would not agree that they even started their clocks at the same time.

Hello stillwonder.

An object is moving inertially or not moving inertially. Clocks do not define this. The clocks of course will only remain synchronized if they are in zero relative motion to each other.

Matheinste
i think what stillwander is getting at is... what will happen to the clocks????... they are moving they were synced while moving... if they are not going to stay synced then which one will be fast which one slow?

Hello neh4pres

Quote:-

---i think what stillwander is getting at is... what will happen to the clocks????... they are moving they were synced while moving... if they are not going to stay synced then which one will be fast which one slow?.....

We are back to square one. Each will, when all other effects are taken into account, consider the other's clock to be running slower than their own. I avoid the word see.

Clock synchronization has no effect on the rate of the ticks. If clocks moving relative to each other are synced at one time they will be out of synch at all other times if their motion relative to each is other remains unchanged.

Synchronizing does not affect the rate at which they tick. To alter this rate you would have to take some action to make the clock do other than it would normally do.

Matheinste

S does not reach his post at the same time as O reaches his post according to O, S's clock does stop when it reaches the post, but reaches his post after O reaches his post.

You have to take the relativistic addition of velocities into account.

$$w=\frac{u+v}{1+\frac{uv}{c^2}}$$

where v is the velocity of O and u is the velocity of S and w is the velocity of S to O as measured by O.

Thus O sees sees the time for himself to travel distance d as d/v, but the time it takes S to traverse distance d is$$\frac{d}{ \frac{u+v}{1+\frac{uv}{c^2}}-v}$$

Also, from your set up, O and S would not agree that they even started their clocks at the same time.
O never left his post. Its the S and S1 that are equidistant from g that make identical travel in opposite directions. and S and S1 reach their posts simultaneously since everything is symmetric in the whole setup.

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Hello neh4pres

Quote:-

---i think what stillwander is getting at is... what will happen to the clocks????... they are moving they were synced while moving... if they are not going to stay synced then which one will be fast which one slow?.....

We are back to square one. Each will, when all other effects are taken into account, consider the other's clock to be running slower than their own. I avoid the word see.

Clock synchronization has no effect on the rate of the ticks. If clocks moving relative to each other are synced at one time they will be out of synch at all other times if their motion relative to each is other remains unchanged.

Synchronizing does not affect the rate at which they tick. To alter this rate you would have to take some action to make the clock do other than it would normally do.

Matheinste

thats where is the rub ... once the clocks are synced in inertial frames (moving wrt each other), they are symmetric. one considers the other to be ticking slower by equal amounts. their being out of sync is the thing thats "virtual" here.

a parallel is, loosely speaking, two identical twins, separated by 1 mile, will see the other one shorter than himself. neither is shorter than the other, they both remain same height.

Hello stillwonder

Quote:-

---a parallel is, loosely speaking, two identical twins, separated by 1 mile, will see the other one shorter than himself. neither is shorter than the other, they both remain same height---

In their own inertial system.

I really have nothing else to add at the moment. It is 5.30 AM here and while time is relative the need for sleep is absolute.

Matheinste.

Hello stillwonder

Quote:-

I really have nothing else to add at the moment. It is 5.30 AM here and while time is relative the need for sleep is absolute.

Matheinste.
lol ..

let me give another example thats mirror image, unfortunately it involves acceleration also, but as you will agree it shouldnt matter if symmetric.

consider two identical rockets S1 and S2, each with two forward pushing thrusters F1, F2 and two rearward pushing thrusters R1, R2. Each have two candles K1, K2 that burns some arbitrary equal amount of time.

(Syncing clocks not really required here) shoot in opposite directions via thruster F1
------------------------------------<-S1**S2->
once F1 is out, light candle K1, now cruising at velocity v
----------------------<-S1(i)--------------------------(i)S2->
candle K1 is out, fire rear thruster R1

------------*<-S1-------------------------------------------------S2->*
R1 out, come to rest, immediately fire thruster F2

-*S1->-----------------------------------------------------------------------<-S2*
F2 out, reached constant velocity
--------------S1->------------------------------------------------<-S2
They pass each other (at mid point), Sync clocks, light candles K2 as they pass each other.
--------------------------------t=0,(i)S1-><-S2 t=0,(i)

Now they see each others' clocks ticking slower.
candle K2 out, **stop**clock** and crash land.

Now if you compare clocks of S1 and S2,

1)which one will show less time? why?
2)if they show same time, what happened to them being started and stopped in the inertial frames and all the slower ticking in between?

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Hello neh4pres

Quote:-

---i think what stillwander is getting at is... what will happen to the clocks????... they are moving they were synced while moving... if they are not going to stay synced then which one will be fast which one slow?.....

We are back to square one. Each will, when all other effects are taken into account, consider the other's clock to be running slower than their own. I avoid the word see.

Clock synchronization has no effect on the rate of the ticks. If clocks moving relative to each other are synced at one time they will be out of synch at all other times if their motion relative to each is other remains unchanged.

Synchronizing does not affect the rate at which they tick. To alter this rate you would have to take some action to make the clock do other than it would normally do.

Matheinste
but clock synchronization does affect what each one perceives the other to be doing.

Dale
Mentor
i dont know how i come back here even after saying i have no problems with SR per se, but only how people go run off tangent with it.
Then I don't understand what you are saying in this thread. What is your point/question?

Janus
Staff Emeritus
Gold Member
O never left his post. Its the S and S1 that are equidistant from g that make identical travel in opposite directions. and S and S1 reach their posts simultaneously since everything is symmetric in the whole setup.
Just replace S1 for O in my response. (I was considering how each ship regarded the other.)

Thus, O determines that each ship reaches their respective starting post at the same time and reach their ending posts at the same time. Both ship's clocks will show time dilation and read an equal amount of time after stopping . O can also be stopped when it determines when S and S1 have reached their end posts. At the end, the clocks S and S1 will read less than the clock at O when brought back together.

However, according to S and S1, the Clock at O does not stop when they reach their end posts, but contiunes to run. The exact determination of how it runs depends on what S and S1 do after they stop their respective clocks.

It still holds true that O and S(or S1) will not agree that the their respective clocks stopped running at the same time. O may determine that this is the case, but S and S1 will not.

i am for now limiting to clocks synced in intertial frames, and started/stopped after acceleration/deceleration. ie whether the time dilation seen in intertial clocks is "virtual" or not.
If there's no difference in the acceleration histories of the two clocks, then the times accumulated by the two clocks will be the same. Time dilation is a symmetrical effect. But if one clock has undergone acceleration(s) that the other hasn't, then the accelerated clock will record less time.

thats where is the rub ... once the clocks are synced in inertial frames (moving wrt each other), they are symmetric. one considers the other to be ticking slower by equal amounts. their being out of sync is the thing thats "virtual" here.

a parallel is, loosely speaking, two identical twins, separated by 1 mile, will see the other one shorter than himself. neither is shorter than the other, they both remain same height.
what i gain from this is if i have a clock and the other person sees it running slow and we both stop as we meet, he will see my clock hand on one # and ill see it on another #.... that is imposable one observer will have to see the others clock as being fast... if i leave earth and travel to our closest galaxy i will come back maybe 100 years older and millions of years will have passed on earth... I know i was the one accelerating... but think of it this way.. if we both traveling at each other for some time then both accelerate the same amount to come to a stop beside each other will we disagree as to who's clock is the one thats slow

OK I GOT IT..... loss of simultaneity . observers are a and b

think of two rockets moving at each other under inertia at a course so that they pass very close. Observer A will look at both clocks when the rockets pass. he will see his own as being T and he will see observer B,s clock as being .5T ..........Observer B will see his clock as being T and he will see Observer A's clock as being .5T ....

Then I don't understand what you are saying in this thread. What is your point/question?
the point is neither classical physics nor SR (or anyone else) is any privileged position to assert statements about underlying reality (if any). "OMG, time *itself* slows down ... aww mannn" sounds like (to me atleast) there is a reality of something called "time" apart from what clocks measure. In physics definitions are operational. time is what clocks measure. length is what a ruler measures. SR just allows us to more accurately measure and predict events (which in turn are measurements) in inertial frames of reference.

Dale
Mentor
the point is neither classical physics nor SR (or anyone else) is any privileged position to assert statements about underlying reality (if any).
What do you mean by "underlying reality"? If you mean something that is not measurable then the topic is inherently unscientific: it is philosophy or religion.

"OMG, time *itself* slows down ... aww mannn" sounds like (to me atleast) there is a reality of something called "time" apart from what clocks measure. In physics definitions are operational. time is what clocks measure. length is what a ruler measures. SR just allows us to more accurately measure and predict events (which in turn are measurements) in inertial frames of reference.
If it sounds like that to you then I think that you misunderstand Einstein. Lorentz was the one proposing an underlying, unmeasurable physical reality which Einstein discarded and obtained a cleaner interpretation that made the same experimental predictions without proposing any unmeasurable underlying reality. That is why it gained such rapid acceptance by the scientific community.

In the title you ask if relativistic effects are real. The answer is, "yes they are real", they have been experimentally measured. If you claim that the relativistic effects are somehow not real then I submit that it is you who is asserting some unmeasurable "underlying reality".

What do you mean by "underlying reality"? If you mean something that is not measurable then the topic is inherently unscientific: it is philosophy or religion.

If it sounds like that to you then I think that you misunderstand Einstein. Lorentz was the one proposing an underlying, unmeasurable physical reality which Einstein discarded and obtained a cleaner interpretation that made the same experimental predictions without proposing any unmeasurable underlying reality. That is why it gained such rapid acceptance by the scientific community.

In the title you ask if relativistic effects are real. The answer is, "yes they are real", they have been experimentally measured. If you claim that the relativistic effects are somehow not real then I submit that it is you who is asserting some unmeasurable "underlying reality".
Having articulated it so well yourself, it amazes me you still missed the point.

Science is about repeatability of experiments (act of measuring) in same/similar settings (equipment) with statistically insignificant aberrations in results (measurements). What is being measured still remains undefined, but results are all one cares about (not saying thats undesirable)

Now, as questionable the "photon bouncing off mirrors clock" is, even taking it as correct, the conclusion is not left at "photon clock reading will be lesser". It is asserted that the underlying "time" has slowed down. This is where the underlying, common reality concept is invoked. If photon clocks have problems at high speeds, use atomic clocks, or handwound clocks. No, no, "the underlying time" has slowed down, so it doesn't matter!! *ALL* clocks will slow down, since all clocks measure the "underlying reality of time", so whats going to be different if "underlying real time itself" slows down?!! This is the kind of argument that makes scientists lazy not to even try to do any experiments and find out.

It was Einstein himself (if i remember correct) who wondered about the identical twins paradox. Its highly presumptuous to assume Einstein himself didnt know how to apply SR to the situation which every graduate and their cocksure professors do it as a matter of fact. What I believe is his question came from he himself not making that leap of faith.

The dynamics of aging are not as rigorously understood and modeled as the photon or handwound clock. In the absence of experiments and/or cost and/or effort etc its conceivable why one would/should use the "underlying reality" argument(since not doing so would mean scrapping everything and just sit there doing nothing). But to start everything from "underlying reality" argument sounds suspicious (to me).

Assuming, penny at hands' length looks same size as the moon. is it same size as the moon? Thats roughly the siprit of "real" versus "virtual" in this thread. I understand the "real" and "virtual" in relativistic situations are much more harder to distinguish, but still they are not coincident.

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Dale
Mentor
as questionable the "photon bouncing off mirrors clock" is
With comments like these, it is hard to take your claims that you "have no problems with SR" as anything but disingenuous and insincere.

Now, as questionable the "photon bouncing off mirrors clock" is, even taking it as correct, the conclusion is not left at "photon clock reading will be lesser". It is asserted that the underlying "time" has slowed down. This is where the underlying, common reality concept is invoked. If photon clocks have problems at high speeds, use atomic clocks, or handwound clocks. No, no, "the underlying time" has slowed down, so it doesn't matter!! *ALL* clocks will slow down, since all clocks measure the "underlying reality of time", so whats going to be different if "underlying real time itself" slows down?!! This is the kind of argument that makes scientists lazy not to even try to do any experiments and find out.
What pompous ignorant arrogance! It is plain to see that either you didn't read the http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html" [Broken] I posted earlier or you didn't understand it. These kinds of experiments have been done for decades! Get your facts straight before making such accusations about the work ethic and dedication of the scientific community.

In any case, the first postulate (which is a testable assumption) requires that all clocks dilate by the same factor, as https://www.physicsforums.com/showpost.php?p=1561105&postcount=3". None of this involves any assertions about unmeasurable underlying reality. As long as the measured "t" in all physical laws is the same we can safely say that time slows down without stepping out of the measurable realm of science and into philosophy about any unmeasurable underlying reality.

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With comments like these, it is hard to take your claims that you "have no problems with SR" as anything but disingenuous and insincere.
lol ... and I thought I was paranoid!! I have no problems per se with any theory that provides results. SR does. I use Newtonian mechanics too. If I had to base my standing on not agreeing on "how the theory got there", then it'll be pretty much every theory.

In any case, the first postulate (which is a testable assumption) requires that all clocks dilate by the same factor, as https://www.physicsforums.com/showpost.php?p=1561105&postcount=3". None of this involves any assertions about unmeasurable underlying reality. As long as the measured "t" in all physical laws is the same we can safely say that time slows down without stepping out of the measurable realm of science and into philosophy about any unmeasurable underlying reality.
Postulate 1 invokes "all physical laws" and you take it to

1. include time dilation ... which isn't something known to you at that "postulation" point
OR
2. you take it as "underlying reality, measurable or immeasurable" which is the point I made earlier.

Also, when time itself is changing, you are taking it as a derived quantity dependent on "physical laws or underlying reality". There is no mechanism given how this is regulated hence making it "immeasurable" by your own definition.

There is no real need to invoke "underlying reality, measurable or immeasurable".
Edit: Although, having a "model" makes it easier to accept and understand.
Whatever you measure is practically all thats there, and it needs to be consistent. Hence the operational definitions in physics.

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malawi_glenn
Homework Helper
Relativistic effects are not real because they are observed in a relative, not objective way.
It depends on how you define "objective way" and "relative way", to me, you are just playing with words if you cant proove your statement.

Regarding your answer in another thread that there is no strong force, I just think you are a crack pot maniac.

Relativistic effects are real in that sense that they affect our measurments. See for example the longer laboratory life time of a fast muon vs. a slow moving muon (in lab frame). And a clock traveling in a weaker gravitational field moves slower compared to a clock in a stronger. Those effects does just not exist on the paper, but also in the real world.

malawi_glenn
Homework Helper
1) Relativity is a stringent science, with a heavy mathematical formalism. Just have a look at Rindler: Special relativity, oxford press.

It could reproduce all known phenomena and predict other results. That is why Einsteins special and general relativity is the paradigm of todays physics.

2) The effects of gravity on the cesium atoms different motion is of course accounted for. Even with this account, the clock still moves to slow, exactly in accordance with Einsteins general relativity.

You know, this is like the people believing in the Moan Hoax.. "The americal flag is moving, but there is no air on the moon, hence it can't blow and set the flag in motion."

But the real explanation is that the flag was set in motion by the astronaut when he stucked it into the ground, and since there are no air resistance, the flag will continue to move forever..

Always think twice.