# Tagged Questions

The union of special (SR) and general (GR) relativity. Use this tag if both SR and GR apply.

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### Is there anything we are aware of that can't be slowed by time dilation?

While thinking about the ambitions of this post: Can radioactivity be slowed through time dilation? I was asking myself, is there even anything that is dependent on time and can't be slowed through ...
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### Can someone conceptually explain time dilation?

Can someone intuitively explain how physically time dilation happens? Please don't explain about the invariant speed of light and the mathematical background, I am familiar with that. I just can't ...
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### Light's speed constancy

Trying to understand the special relativity I faced a problem,and have a question, well, with the speed of light being constant in every frame, the operation s=d/t (s for the speed of light d: ...
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### Reference request for relativistic imaging

Being a high-school physics teacher, I always am searching for compelling and different approaches to the subject. In the case of (special) relativity a frequent curiosity arises while discussing what ...
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### What is the benefit of the relativistic effects (time dilation and length contraction)? [closed]

Can an observer ever experience the relativistic effects, or he just can observe them. For an observer these effects happens only on other objects that he observe, but can he realize if he is ...
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### If mass increases as velocity increases, does gravity increase as well? [duplicate]

The way I understand it, velocity and mass are tied together with relativity. As I increase in velocity, I increase my mass until my mass is so great that it would take more energy than the entire ...
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### Tensor manipulation and showing equality

Im taking GR for the first time and it is definitely throwing me for a loop. The question I am working on is this: Prove that if a contravariant tensor $A^{uv}$ is symmetric, then it remains ...
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### Universe expansion and general relativity [closed]

If the universe is expanding faster and faster, won't we reach a moment where the general relativity will make the mass so big, that the universe will have to decrease its acceleration?
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### Are gravitational waves constrained by special relativity (speed of light)? [duplicate]

In Lawrence Krauss's excellent book "Universe from Nothing" and his related lectures, he cites findings of the BOOMERANG-instrument observations in Anarctica as used to measure the diameter of ...
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### Using gravity to send messages (at the speed of light) [duplicate]

I've been wondering what the current state of the art (both theoretically and practically) for sending messages using changes in a gravitational field is, and I have had a hard time finding ...
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### Where would you go to get feedback, advice and assistance for a new theory of physics? [closed]

I know that crackpots are constantly running down physicists to pitch them on a "new theory" that solves everything. This has understandably led to extreme skepticism for anyone not affiliated with a ...
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### Three time dimensions and one spatial dimension degeneracy

Is there a sort of degeneracy in the space-time metric for our universe? What I mean is that it seems you would observe all the same properties of our universe if you simply placed a minus sign in ...
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### Are there any known non-zero mass objects travelling at almost $c$ observed in the universe so far?

Have we ever observed a body or particle with non zero mass traveling at almost $c$? I'm asking this because according to relativity as an object approaches light speed it's mass approaches infinity, ...
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### Double the mass in the universe, double the inertia

If I double (halve) the mass in the visible universe, will my inertia double (halve)? I think it should, at least as soon ''I have received the news of this doubling''. But what does the General ...
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### Inertial Frames of Reference - Inertial vs. Accelerated Frames

According to Robert Resnick's book "Introduction to Special Relativity", a line states the following as the definition of an inertial frame of reference: "We define an inertial system as a frame of ...
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### Space: a vacuous void or an entity?

I am a chemist and, until recently, a senior Research Manager with a major chemical company. Please excuse the potentially naive ramblings of an idiot in what follows, but I do not have the ...
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### Special Relativistic approximation to GR

Some time ago I was talking to a professor in college about some of the fundamental aspects and origin of General Relativity. I was surprised to learn, in fact, that a pretty good approximation to GR ...
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### F=ma is true in an accelerating coordinate system [closed]

There are plenty of similar topics about the physical or intuitive meaning of the equivalence principle or statement such as ''laws of physics are true in every frame of reference''. Usually answers ...
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### Real and relative velocity formula

What i need is a thing more complicated than the usual relative velocity formula. Imagine a radar. You are at the center, moving at some angle, but lets make it clear, you are always at the center. ...