Find solution
Which objects reference my ViewController strongly?

When two objects are moving at a steady velocity in relation to each other at near relativistic speeds, does the mass look different depending on your frame of reference?

  • According to the theory of relativity, given two objects moving at a steady velocity in relation to each other, it is impossible to tell which objects are and aren't moving. But AIUI at near relativistic speeds, the mass of the matter becomes nearly infinite. Could the mass not be measured? And if so, what would the result be? Does the mass actually look different depending on your frame of reference? I know there is something wrong with this logic. Can a real physicist please tell me what it is?

  • Answer:

    There's a little bit of confusion in your question. If you have two objects moving with respect to each other, A and B, it's not impossible to tell which is or isn't moving - but that question depends on your frame of reference, that is, the perspective from which you're looking at them. If you're outside, then both can look like they're moving. If you imagine yourself traveling alongside A, then B is moving and A is still. Similarly, if you're traveling alongside B, A is moving and B is still. What relativity says is that none of these is "more right" - these are all perfectly valid frames to see the them interact. This is because there is literally no way for you to tell if you're "moving" alongside a moving A, or if you're both standing "still" - since they're indistinguishable, in relativity that's not even a distinction that makes sense. We then need to have a system of physics that gives us sensible answers no matter if you're looking at the system from A's perspective, or B's, or some outsider, C. This symmetry, combined with the fact that the speed of light is always the same, is what gives us the bizarre results of special relativity. The short answer to your question about mass/density is that yes, the density looks different depending on your frame of reference. Each thinks the other is very very heavy; that's because each sees the other moving very very fast. So yes, measuring the density does allow us to figure out whether or not something is moving quickly - because it is possible to tell which objects are moving or not from the perspective of a particular reference frame; special relativity just says that, in a different equally valid reference frame, you might get a different answer.

Lucian Wang at Quora Visit the source

Was this solution helpful to you?

Other answers

Understanding frames of reference is really hard. First of all, It is really hard to measure the mass of an object that is moving at near light speeds relative to your frame of reference. And if you are moving at the same speed as the object you are measuring, you are both in the same frame of reference and you won't detect any change of mass at all. The change in mass from relativity comes from moving in relation to one another. But this has been measured and is an observable effect.

Todd Gardiner

IANAP, but the answer to the last question is that you would not measure a different density and so you would not be able to tell if you are moving with a constant velocity or not. One of my favorite principles of the theory of relativity is that if you are in a reference frame that is moving at a constant velocity (not accelerating), there is absolutely nothing you can do to measure your own velocity (without looking outside and using some prior knowledge). So whenever I come across a thought experiment like the one you described, I ask myself the above question. In your case, suppose you were in a closed box moving close to speed of light. Then if the density changes then you could measure this change in density to evaluate the speed of your box. This is not possible. So, the answer is that time dilation and length contraction all act in a way that the density you measure would be the same as in a moving reference frame or in a rest reference frame. Hope this makes sense!

Rohit Sammeta

Related Q & A:

Just Added Q & A:

Find solution

For every problem there is a solution! Proved by Solucija.

  • Got an issue and looking for advice?

  • Ask Solucija to search every corner of the Web for help.

  • Get workable solutions and helpful tips in a moment.

Just ask Solucija about an issue you face and immediately get a list of ready solutions, answers and tips from other Internet users. We always provide the most suitable and complete answer to your question at the top, along with a few good alternatives below.