## TomLikesPhysics 3 years ago If they (scientists) accelerate some particle (e.g. a proton) in their accelerators they can get some high velocity like 0.999...*c. As I understand they can never reach c because Einstein does not allow that kind of stuff but isn´t their total velocity higher than c if I also consider that the earth is going around the sun and our galaxy is also moving with some speed around some center or rotation.

1. Mani_Jha

Nice question. Speed is a relative quantity. It will be different when you observe it from different places. So which is right? That's why we have developed inertial frames. Earth is one, we measure velocities from Earth and consider it right. From space, you will get a different value, but you just shouldnt, because the earth is accelerating with respect to that stationary space. So, we cant consider space as an inertial frame. I m not very sure about this, as I have used Newtonian Physics to explain Eienstin's. :P

2. shubham

First thing that you need to understand is Speed of light, c is same from any frame of reference. Suppose you are travelling in a car at speed, v relative to the ground. Now, Do you think velocity of light particles ( photons ) will be different as seen from ground and car, I mean like c and c-v.

3. TomLikesPhysics

I "know" light always travels with the speed of light but in this example I want to talk about some particle with rest mass like a proton or electron. So say that someone who is sitting in the sun is looking at some particle in an accelerator. Than in his frame of reference he should consider the earth´s movement around the sun and it´s spin.

4. Mani_Jha

Well, the reference frame of the sun is not an inertial frame, because earth is accelerating with respect to it. So, what he measures shouldnt be correct.

5. TomLikesPhysics

k. I also found accidentally an answer in the Physics Video from Yale (13 Lorentz Transformation – 34 minutes) on iTunesU. Apparently it is not possible to add velocities so simply. There goes my nobel prize. ;)

6. Mani_Jha

Lol, That happens. You've got to keep thinking like that, and post questions like this. Maybe someday, you will ask a question which will lead to your nobel prize!(Share it with me for giving you this advise :P)

7. Mani_Jha

Hey, where are you from?

8. TomLikesPhysics

I´m from Germany. Why?

9. Mani_Jha

Just wanted to know you more :)

10. TomLikesPhysics

Alright, well thanks for your help Mani Jha (and shubham). I guess we will meet again on this site :) until then have a good time - cu