Special relativity:Reality or measurment error(?

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Discussion Overview

The discussion revolves around the nature of simultaneity in the context of special relativity, exploring whether the differences in perceived simultaneity are due to measurement errors or if they reflect a deeper reality. Participants examine thought experiments, such as the train and track scenario, and raise questions about the implications of relativity on concepts like time dilation and length contraction.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Exploratory

Main Points Raised

  • Some participants argue that the differences in simultaneity perceived by observers in different frames of reference are merely measurement errors, suggesting that an absolute notion of simultaneity might exist.
  • Others contend that there is no way to determine whose measurements are correct, emphasizing that simultaneity is fundamentally a matter of definition rather than measurement.
  • One participant highlights that simultaneity cannot be universally agreed upon across different frames, as each frame has its own conflicting definition.
  • There is a discussion about whether phenomena like time dilation and length contraction are real effects or simply artifacts of measurement, with some asserting that these effects do indeed occur.
  • Questions are raised about the philosophical implications of relativity, particularly regarding the nature of reality and our understanding of simultaneity.
  • Participants express uncertainty about whether events can truly be simultaneous or if this is a concept that cannot be definitively established.

Areas of Agreement / Disagreement

Participants do not reach a consensus; multiple competing views remain regarding the nature of simultaneity and the implications of special relativity. The discussion reflects a range of opinions on whether the effects described by relativity are real or merely measurement errors.

Contextual Notes

Some discussions touch on the limitations of defining simultaneity and the challenges posed by the absence of a single reference frame. The conversation also highlights the philosophical questions surrounding the interpretation of relativistic effects.

  • #31
I did a Google search on the phrase "relativistic velocity composition formula" and found only 14 hits but I couldn't get a clear definition of the formula. I would think a legitimate formula would have hundreds, if not thousands, of hits. Could you please point to a reference that defines it? The reason I ask is that I have never heard of a formula that would allow you to obtain the speed of one photon relative to another one.
 
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  • #32
Shyan said:
This question is not related to the previous ones but I don't want to make a new thread for it.
Imagine we have a source of light which can emit photons in two direcions.We take the refrence frame connected to the light source,our preferred refrence frame.Then we emit photons from two sides simultanously(So photons move in opposite direcions).If we use relativistic velocity composition formula to obtain the speed of one of the photons relative to the other one,we obtain c.What it means?How can you explain it?
thanks

It is just a consequence of putting in a legitimate?? value, c, (for a massless particle) for velocities into the SR relative velocity formula. Remember the formula returns the value of the velocity of one photon as measured?? from the other photon's point of view. Of course whether or not a photon has a valid reference frame, or point of view, is often the subject of some, mostly informed and thought provoking, heated argument in this forum. However, I prefer to avoid the question and stick to subluminal speeds.

Matheinste.
 
  • #33
ghwellsjr said:
I did a Google search on the phrase "relativistic velocity composition formula" and found only 14 hits but I couldn't get a clear definition of the formula. I would think a legitimate formula would have hundreds, if not thousands, of hits. Could you please point to a reference that defines it? The reason I ask is that I have never heard of a formula that would allow you to obtain the speed of one photon relative to another one.

Huh? Google says "564,000 results". Try

Try http://www.google.com/search?q=relativiistic+velocity+addition
 
  • #34
I have another question.In SR there is a notion called rest mass.but we know sth which is at rest in one frame of refrence,is moving in another.So How can we define rest mass when there is nothing called rest?
 
  • #35
Daverz said:
ghwellsjr said:
I did a Google search on the phrase "relativistic velocity composition formula" and found only 14 hits but I couldn't get a clear definition of the formula. I would think a legitimate formula would have hundreds, if not thousands, of hits. Could you please point to a reference that defines it? The reason I ask is that I have never heard of a formula that would allow you to obtain the speed of one photon relative to another one.
Huh? Google says "564,000 results". Try

Try http://www.google.com/search?q=relativiistic+velocity+addition
You have to put quotes around a phrase (and it helps if you spell it right), otherwise it searches for the words anywhere in a document. Now, when I do it, it finds 15 hits, because it found this webpage.

In any case, I'm still waiting for an answer to my question.
 
  • #36
Shyan said:
I have another question.In SR there is a notion called rest mass.but we know sth which is at rest in one frame of refrence,is moving in another.So How can we define rest mass when there is nothing called rest?
In SR, you must select just one frame at a time. Anything at rest in that frame will exhibit its rest mass.
 
  • #37
Hey! read 1 of the TS original questions. super interesting. So if we have a 2m car, a 1m hole and an stationary observer. now the 2m car is accelerated to approx c. then the observer measures the car nw, it is less than 1m, will it fall into the hole? (since the hole is not moving wrt to observer, even if he measures it again, it will still b 1m right?)

hmm from the car driver pt of view, he will always measure his car at 2m right? but he will see the hole contract? if so...then he (even more) won't fall into the hole from his pt of view.
 
  • #38
The car would contract he just wouldn't be able to measure it with a contracted ruler, so he would measure his car to still be 2m but it could still be smaller than the hole.

Same problem of two observers both measuring each other to contract doesn't fit into one single reality. I would think that since the car does the acceleration it is the one that actually contracts, but then acceleration doesn't cause spacetime dialation...

Earth has never contracted due to an object traveling close to the speed of light either.
 
  • #39
ghwellsjr said:
I did a Google search on the phrase "relativistic velocity composition formula" and found only 14 hits but I couldn't get a clear definition of the formula.
Usually terms for equations don't actually have the word "formula" at the end of them, if you search for "relativistic velocity composition" you get 1,990 hits and if you search for the more common synonym "relativistic velocity addition" you get 10,300 hits.
 
  • #40
why would it still be smaller than the hole? if the stationary observer measures it again(when it is traveling at near speed now) but this time it is less than 1m, shouldn't it fall into the hole?

sry if i seem slow. this concept is quite non intuitive.=x
 
  • #41
The saying goes that you can't measure your own length contraction because your ruler would contract by the same amount. So he would measure himself as being the same size but he would still be contracted to a smaller size.

But, he would only be contracted in the direction of motion so if he was traveling head on into the hole then he still wouldn't fit because his ship would still be just as wide.
 

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