Are relativistic effects real ?

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SUMMARY

The forum discussion centers on the reality of relativistic effects, particularly time dilation and length contraction as described by Einstein's theory of relativity. Participants debate whether these effects are genuine or merely perceived illusions, emphasizing that all motion is relative and that observers in different frames will measure time and distance differently. Key points include the assertion that clocks do return to their original measurements when observers are at rest relative to each other, and the idea that length contraction is a real phenomenon, not just an optical illusion. The discussion highlights the complexities of understanding these relativistic effects and their implications for measurements in physics.

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  • Understanding of Einstein's theory of relativity
  • Familiarity with concepts of time dilation and length contraction
  • Knowledge of inertial reference frames
  • Basic grasp of spacetime diagrams
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  • #31
DaleSpam said:
You didn't answer this before when I posed it, but do you consider the muons which reach the surface of the Earth to be "virtual", do they just "appear" to reach the earth, or do they really reach the earth?

the muon is a particle and hence accelerates to its speed v. that definitely isn't in the same category as current discussion where the time dilation and length contraction of inertial frames is discussed.
 
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  • #32
Ich said:
What illusion? Therein lies the solution.

But he would stop his clock at the same time S reaches his post. Thats how O setup his posts and rockets. So either his computations are wrong, or his bare eye observation is tricking him.
 
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  • #33
matheinste said:
Hello stillwonder

Quote:-

--- Hence there IS not such thing as "purely inertial but at motion wrt each other" set of frames.-----

Are you saying that two objects, each moving inertially, cannot be in relative motion. Or do you want to reword your statement

Matheinste.

Let me put it this way: how can there be two mutually in motion inertial frames, neither of which ever accelerated?
If one frame must accelerate at some point or the other to reach speed v, then your assertion that "that acceleration spoils the game, SR cannot be applied" implies "SR cannot be applied in any situation". This is logical conclusion of your assertion that no acceleration be used at no point. My assertion is "SR should be applicable when clocks are synced in inertial frames, and rest of the experiment happens in the inertial frames. How the inertial frame got to their respective velocities earlier to syncing, or what happens to them after the experiment are irrelevant"
 
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  • #34
neh4pres said:
OK new question if i accelerate to a point where i can travel ten lightyears in 5 years. then stop accelerating and just float under my inertia. how can a light ray sent from my start point ever catch me?

light will always be faster than anything in vacuum by definition. so it will eventually catch you.
 
  • #35
stillwonder said:
the muon is a particle and hence accelerates to its speed v. that definitely isn't in the same category as current discussion where the time dilation and length contraction of inertial frames is discussed.
No, it doesn't. The muon is created in the upper atmosphere already moving at relativistic speed. It does not accelerate, but moves inertially its whole life. It is a perfect and exact example of precisely this discussion.
 
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  • #36
stillwonder said:
light will always be faster than anything in vacuum by definition. so it will eventually catch you.

i've been told that as long as you stay at constant acceleration near speed c light signal sent from behind you will never catch you
 
  • #37
stillwonder said:
Let me put it this way: how can there be two mutually in motion inertial frames, neither of which ever accelerated?
If one frame must accelerate at some point or the other to reach speed v, then your assertion that "that acceleration spoils the game, SR cannot be applied" implies "SR cannot be applied in any situation". This is logical conclusion of your assertion that no acceleration be used at no point. My assertion is "SR should be applicable when clocks are synced in inertial frames, and rest of the experiment happens in the inertial frames. How the inertial frame got to their respective velocities earlier to syncing, or what happens to them after the experiment are irrelevant"
You are making a classic error here. A frame is a coordinate system, not a material object. SR applies to inertial coordinate systems*, but is in no way restricted to the analysis of inertially moving objects only within those coordinate systems. You can use SR to analyze arbitrarily moving bodies provided you do so from an inertial coordinate system in flat spacetime.

*Technically you can use SR in non-inertial coordinate systems as long as spacetime is flat, but this requires a lot of care.
 
  • #38
DaleSpam said:
No, it doesn't. The muon is created in the upper atmosphere already moving at relativistic speed. It does not accelerate, but moves inertially its whole life. It is a perfect and exact example of precisely this discussion.

muon being a subatomic particle, claims of being able to tell when and where it was born and at what speed with arbitrary precision is inviting trouble from quantum fellas. did someone knock already ? :-)
 
  • #39
neh4pres said:
i've been told that as long as you stay at constant acceleration near speed c light signal sent from behind you will never catch you
This is correct, but you should specify constant proper acceleration. Constant coordinate acceleration is not possible.
 
  • #40
stillwonder said:
muon being a subatomic particle, claims of being able to tell when and where it was born and at what speed with arbitrary precision is inviting trouble from quantum fellas. did someone knock already ? :-)
I will let conservation of momenum answer the door. Besides, you don't even need very high precision, let alone arbitrary precision. Your response is simply a weak attempt to dismiss important physical evidence.

You ask if SR is "real". Relativistic muons really reach the surface of the earth, it is not just appearances. If you don't like the SR explanation then I challenge you to explain the observed evidence without SR. It is certainly possible to posit an alternative theory, but you cannot ignore experimental evidence when you are asking questions about whether a theory is real.
 
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  • #41
Hello stillwonder.

For two objects in relative motion, at least one of them must have undergone acceleration at some point. I think i would accept that statement but there couild be some deeper considerations, not relevant to this thread which may apply to the statement. But this does not mean that an object's total history is always relevant in any situation. If two objects are, despite their previous history, at zero relative velociy in inertial motion with respect to each other at some time then we can ignore their history and start from that situation. For all we know they may have always been in this relation to each other. So an acceleration by one, or unequal accelerations, result in asymmetry if they then return to their previous inertial state with regard to each other.

There may be other considerations as to how an expanding universe may effect relative motion and so on but that is not immediately relevant to the point.

Matheinste.
 
  • #42
DaleSpam said:
You are making a classic error here. A frame is a coordinate system, not a material object. SR applies to inertial coordinate systems*, but is in no way restricted to the analysis of inertially moving objects only within those coordinate systems. You can use SR to analyze arbitrarily moving bodies provided you do so from an inertial coordinate system in flat spacetime.

*Technically you can use SR in non-inertial coordinate systems as long as spacetime is flat, but this requires a lot of care.

How can I be making error when I am doing my experiment in frames attached to inertial observers? I am merely giving the whole setup to show how they got to syncing their clocks and claiming their "inertiality". The frames are automatically defined for inertial observers.

I don't know what's the point of discussing a perfectly flat space "in practice" since in practice, who will go where to perform such an experiment? To say, "oh your clock has mass so you cannot apply SR since its disturbing spacetime" would leave no place where SR will be practiacally applicable.
 
  • #43
DaleSpam said:
I will let conservation of momenum answer the door. Besides, you don't even need very high precision, let alone arbitrary precision.

Your response is simply a weak attempt to dismiss important physical evidence. You ask if SR is "real". Relativistic muons really reach the surface of the earth, it is not just appearances.

light will also turn a wheel. doesn't mean wheel was born spinning. i am just questioning how a subatomic particle with inalienable rights to show wave-particle duality and quantum behaviour be dragged into SR without complicating matters?
 
  • #44
matheinste said:
Hello stillwonder.

For two objects in relative motion, at least one of them must have undergone acceleration at some point. I think i would accept that statement but there couild be some deeper considerations, not relevant to this thread which may apply to the statement. But this does not mean that an object's total history is always relevant in any situation. If two objects are, despite their previous history, at zero relative velociy in inertial motion with respect to each other at some time then we can ignore their history and start from that situation. For all we know they may have always been in this relation to each other. So an acceleration by one, or unequal accelerations, result in asymmetry if they then return to their previous inertial state with regard to each other.

There may be other considerations as to how an expanding universe may effect relative motion and so on but that is not immediately relevant to the point.

Matheinste.

"at zero relative velociy in inertial motion with respect to each other"

so you propound the importance of zero relative velocity over non-zero relative velocity?
 
  • #45
stillwonder said:
Let me put it this way: how can there be two mutually in motion inertial frames, neither of which ever accelerated?
stillwonder said:
How can I be making error
An inertial frame never accelerates relative to another inertial frame by definition. Your error is in thinking that one reference frame (coordinate system) must accelerate in order to have some velocity relative to another reference frame (coordinate system).
 
  • #46
stillwonder said:
i am just questioning how a subatomic particle with inalienable rights to show wave-particle duality and quantum behaviour be dragged into SR without complicating matters?
So? If you feel it is complicated then put some mental effort into it.

I notice that you are still avoiding the evidence. The muon example is just one of many. I would recommend that you read the http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html" . SR is real; it is as well-tested as any theory has ever been. If you want to dissmiss it as "appearances" then you have a lot of explaining to do.
 
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  • #47
Hello stillwonder

Quote:-

---so you propound the importance of zero relative velocity over non-zero relative velocity?--

No, zero is just another velocity. All it says that they are not moving with respect to each other. If they are in inertial relative motion, any velocity will produce the same argument of asymmetry introduced by unequal acceleration leading to different spacetime paths between two events.

Matheinste.
 
  • #48
DaleSpam said:
An inertial frame never accelerates relative to another inertial frame by definition. Your error is in thinking that one reference frame (coordinate system) must accelerate in order to have some velocity relative to another reference frame (coordinate system).

i asked myself , and nope that's not what i am thinking :)
once the coordinate systems are in constant velocity with each other, thye are syncing their clocks and declaring themselves "inertial frames" from that point forward. my objection was to the requirement that the observers be "born" at relative velocity relative to each other instead.
 
  • #49
matheinste said:
Hello stillwonder

Quote:-

---so you propound the importance of zero relative velocity over non-zero relative velocity?--

No, zero is just another velocity. All it says that they are not moving with respect to each other. If they are in inertial relative motion, any velocity will produce the same argument of asymmetry introduced by unequal acceleration leading to different spacetime paths between two events.

Matheinste.

i am missing something here perhaps... isn't having the clocks synced when they are at constant velocity relative to each other and stopping the clocks before any deceleration (or acceleration) not enough to establish inertial frames?
 
  • #50
DaleSpam said:
So? If you feel it is complicated then put some mental effort into it.

unlike observers in thought experiments, I have limited time. i understand the detour you want me to take is not different from what i did to the OP's thread (and someone graciously made this its own thread, thanks!)

I notice that you are still avoiding the evidence. The muon example is just one of many. I would recommend that you read the http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html" . SR is real; it is as well-tested as any theory has ever been. If you want to dissmiss it as "appearances" then you have a lot of explaining to do.

i don't 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. thanks for the link.
 
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  • #51
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
 
  • #52
stillwonder said:
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.
 
  • #53
matheinste said:
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?
 
  • #54
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
 
  • #55
Janus said:
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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  • #56
matheinste said:
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 that's "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.
 
  • #57
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.
 
  • #58
matheinste said:
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 that's mirror image, unfortunately it involves acceleration also, but as you will agree it shouldn't 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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  • #59
matheinste said:
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.
https://www.physicsforums.com/showthread.php?t=236978
 
  • #60
stillwonder said:
i don't 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?
 

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