# What is Special relativity: Definition and 996 Discussions

In physics, the special theory of relativity, or special relativity for short, is a scientific theory regarding the relationship between space and time. In Albert Einstein's original treatment, the theory is based on two postulates:
The laws of physics are invariant (that is, identical) in all inertial frames of reference (that is, frames of reference with no acceleration).
The speed of light in vacuum is the same for all observers, regardless of the motion of the light source or observer.

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1. ### Special Relativity: What are the events in the question?

This was part of a test we did a while back, so I forgot how exactly I solved it, but I think I basically solved the question by putting the values into equations and hoping for the best, since I didn't have a good understanding back then. Since then, I have learnt that it's a good idea to break...
2. ### B LIGO to go back online today after updates

From this morning's Economist briefing: The Laser Interferometer Gravitational-Wave Observatory—the world’s most sensitive device for spotting gravitational waves—starts up again on Wednesday after a three-year hiatus for upgrades. LIGO is designed to detect subtle ripples in space and time...
3. ### I Time dilation with respect to non-stationary reference frame

Let's consider three observers A, B and C. The experiment starts at t = 0. A is 'absolutely' stationary. B immediately (please imagine it) starts moving at speed v1 with respect to A. C immediately starts moving at speed v2 with respect to A in the same direction as B. Let's say A measures a...
4. ### B Perception of velocity in special relativity?

If an object is going close to the speed of light, will outside frames of references perceive the moving object as going slow or fast?
5. ### Solving a Problem with Interchanging Field Tensors

Exercise: Solution: The result is correct, but I'm unsure about equation from 29 to 30 where right-hand side became just the covariant dual field tensor. I assumed that I could interchange the covariant dual- and normal covariant field tensor, but don't think it's possible since matrices...
6. ### Special Relativity - Which reference frame experiences which time?

This was a practice question, so it had the answer with it, which is 31 minutes. However, I'm confused as to why Lisa experiences T0. It isn't exactly an event happening in Lisa's rocket, but rather her just moving through space. From her perspective, it should look like Earth is moving at the...
7. ### ChatGPT Results: Testing Special Relativity

Hi guys, I have heard a lot of claims about ChatGPT and how it is going to put a lot of people out of work. I have a friend who is a teacher of humanities and he is fearful of losing his job in the long term. People seem to be in awe at the thing and think it understand what is saying. So I...

48. ### B Time dilation on rotating disk according to clocks on the disk

Obviously, a third observer who is at rest with respect to the disk will see that the clock on the outside has a much faster velocity than a clock on the interior of the disk, so clearly the outside clock will show that it has measured less time. But that's one question. What about looking at...
49. ### I The Killer Crate Paradox

Hi Physics Forums, I've devised a thought experiment called the "Killer Crate Paradox" to put a spotlight on an issue I'm having, with regards to understanding length contraction, specifically in instances where multiple objects are observable and they have different velocities and directions...
50. ### B Sagnac effect for matter beams

Hello, I have recently come across this article by Rizzi and Ruggiero, called "The Relativistic Sagnac Effect: Two Derivations": https://arxiv.org/pdf/gr-qc/0305084.pdf In section 3, the authors derive the Sagnac proper time difference for all beams (light beams and matter beams, including...