# Is there a stationary frame of reference?

My understanding of relativity is at the beginner level, so please bear with me to help a beginner to understand. Something which I don't understand is consider if you travel close to the speed of light you will notice effects occurring, for example in this video. https://www.youtube.com/watch?v=-CIs3jOnfiM it says that close to the speed of light you will see distortions.

Now it is also said that there is no stationary position, everything is moving relative to other objects. However, lets say there are three people, one is myself, I sit still. Person A and B are sitting next to me then they go off in opposite directions from me and exert exactly the same amount of energy (thrust) for the same amount of time to accelerate away from me. Both of them came close to the speed of light, of course in opposite directions to each other. Then they came back to me to report their findings.

Could it be that person A experienced more distortions than person B, when they were travelling close to the speed of light? Would this indicate that I am therefore not actually stationary, but in fact I was moving some speed relative to the speed of light?

What if then I set off at a high speed with my 3 friends together, we are all travelling together in the same direction, at what we think is half the speed of light then conduct the same experiment. Wouldn't then at least one of them person A or B come to experience "effects" before the other? Of course one of them would get to the speed of light faster than the other right?

When I said "effects" I mean what is explained in the first video at Youtube.

If person A and B experience different degree's of "effects", wouldn't that indicate that there is really a stationary frame of reference?

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Yes you're if then else statements are correct. The result in both experiments would be that A and B would report the same "distortions". – Mew Feb 1 '13 at 7:31

A modern view in physics is that when we define a term such as "stationary," we should attempt to do so operationally meaning in terms of some sort of a measurement one can perform. Before we start thinking about the existence of a stationary frame in the real world, we need to define such a frame operationally. Once we have a definition that is sufficiently operationally precise, we can go out into the world and make measurements to see if there exists anything out there that satisfies our definition.

I would recommend that you try to define "stationary frame" in some operational way such that the resulting definition aligns with your intuition for what stationary should mean, and I'll bet you won't be able to do it.

Fortunately, there is another term in physics that is pretty close to what you might want, the notion of an "inertial frame." An inertial frame is one in which if you were holding an accelerometer still in that frame, then the accelerometer would indicate zero. So basically, such a frame is one which is not accelerating. What's interesting about inertial frames, however, is that if you are in an inertial frame, then any other observer moving relative to you with constant velocity will also be in an inertial frame. In other words, if that other observer were holding an accelerometer still relative to him/herself, then he/she too would measure zero acceleration. In such a situation, you might be inclined to claim that you are the one standing still, and the other observer is moving. However, it is a basic fact of physics that the laws of physics are the same in all inertial frames, so from an operational viewpoint, there is no way to distinguish between inertial frames.

It is in this sense that saying that one inertial observer is stationary while another is moving is not really appropriate. It is also because of this that you will often hear statements like "there is no absolute rest" or "motion is relative" or "it only makes sense to talk about relative motion" etc.

The bottom line is that all frames can be categorized as either inertial or non-inertial. All inertial frames are physically equivalent and are the closest you can get to being "stationary" in some sense, while non-inertial frames are pretty far from what most people would call stationary since acceleration is involved.

I hope this helps! Let me know if you want more! (I know I didn't address the questions about distortions etc., but I felt the answer was getting too long).

Cheers!

Addition. Just for the sake of more completeness; it's important to note that infinitely large frames of reference that are inertial don't actually exist. There are, however, "local inertial frames," namely it is possible to devise a physical situation in which a small region around you satisfies the definition of an inertial frame outlined above, but as you move further away from this region, the frame becomes a worse an worse approximation to being inertial. I'd encourage you to explore this further since this point is especially important in GR for example. Here and here would be good places to begin to learn more.

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