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

learn more… | top users | synonyms

1
vote
2answers
940 views

If time stops for an object, does that object feel gravity?

As far as I understand The GTR, it is said that Mass bends space-time which causes gravity. So every Mass in this universe is flowing through space-time example earth is moving along with space-time ...
0
votes
2answers
178 views

Does relativity violate uncertainty principle?

Let us say I sit on an electron. According to me the electron is at rest. Also, I will know the position of the electron accurately as I can take the electron as the origin. So, I know both position ...
0
votes
2answers
246 views

Can relativistic momentum (photons) be used as propulsion for 'free' after the initial generation?

In discussing this question about propelling a spacecraft with photons and their relativistic momentum, the author asked that I restate my comment as another question. If photons can really be used ...
0
votes
1answer
12k views

Could the shadow move with faster-than-light speed? [duplicate]

If I make a huge laser with a figure for shadow in front of the laser, and I shine it on to the moon, will I see the light from the laser AND the shadow moving the same speed? (I read somewhere the ...
0
votes
2answers
347 views

What if a normal digital clock used to measure time in twin paradox?

Last night I was watching a youtube video about twin paradox. It still continues to baffle me :). In that video, the speaker conceptualizes a clock that measures time by reflections of light. If we ...
0
votes
2answers
205 views

What will happen if we use a speed greater than light speed and find a body'motion and energy relative to it?

In Einstein's papers, he used light speed as a reference speed. What if we use a greater finite speed and do the same calculations. Won't this greater speed then be the limit.
0
votes
3answers
135 views

How can you explain objects of unequal masses falling at the same rate using GR?

Isn't gravity caused by the curvature of space-time, and the stronger it's curved the stronger the attraction? it makes more sense to me that if a heavier object is falling on earth it would fall ...
0
votes
4answers
659 views

What is the proper time interval for simultaneous events?

Let us take a rod of length L and the two ends A and B have two photon guns. A----------------------B Let the end A fire a pulse (event ...
0
votes
2answers
108 views

Minkowski metric and definition of coordinate differentials?

This is probably a really silly confusion I have about the definition of “coordinate differentials”, which I thought were things like $dx,dy,dz$ etc. The Minkowski line element ...
0
votes
2answers
11k views

If nothing in the universe can travel faster than light, how come light can't escape a black hole? [duplicate]

Possible Duplicate: How does gravity escape a black hole? If nothing in the universe can travel faster than light, how come light can't escape a black hole? I mean, Einstein's relativity ...
0
votes
2answers
405 views

length contraction question

we know from eintein's theory of relativity that lets say, a ruler is travelling to a speed if light, then we can say that the ruler (from our view as observers) has shorten. but why, lets say we have ...
0
votes
3answers
98 views

Equal and opposite reaction at light speed

My knowledge of physics is very limited. And this question is only really to help me put to rest a question i have had for some time. I would like the answer to be a simple one as i am not really in ...
0
votes
2answers
258 views

Is it really “time” that is dilating?

Consider the following variation of the twin paradox: A clock or a biological system ultimately is an electromagnetic system. First, let’s devise a new time measuring device. Imagine a tank of ...
0
votes
2answers
1k views

Am I faster than my shadow?

I guess that everything that happens to me (or I do), happens before my shadow "records" the information. Is that right? Is it the same for any observer?
0
votes
1answer
83 views

Why is the speed of light being invariant and finite in all inertial reference frames?

I understand the basics of Lorentz transformation and Riemann Geometry but I still cannot understand why the speed of light is the same in all inertial references. Has anyone ever researched about ...
0
votes
3answers
135 views

can a spaceship decelerate relativistically? [closed]

Say I have a spaceship, and on board is a laboratory set to accomplish some sort of experiment, simulation, or computation which might take upwards of a few hundred years or more to complete. Instead ...
0
votes
2answers
157 views

Meaning of Proper time

Sorry for a bit of a basic question, but want to clarify things in my head. Is proper time quantified by the amount of physical process that an object, or physical system undergoes, for example the ...
0
votes
3answers
335 views

Why does time slow down the closer you are to a mass?

When ever i look this up all I get is sites saying how its because general relativity says "-" why does it do it though? it is because there is more motion near gravity than further away? Or is it ...
0
votes
3answers
266 views

On Group Theory: Symmetry Groups and Our Interest

Over the past few years, I've been doing a lot of self education in the Quantum Mechanics and General Relativity, and of course, there are mathematical elements of both doctrines that are matrices. ...
0
votes
1answer
179 views

Apparent paradox in special relativity: transmitting a message and setting off after it

I have a question about special relativity, which is set in the context of the science fiction anime Voices of a Distant Star, though it is independent of that context. Mikako goes on a spaceship ...
0
votes
3answers
231 views

Violation of Newton's 3rd law

I'm just expressing my guess. Let two particles A and B experiences forces $F_1$ and -$F_2$ between them and let guess also there are two observer, one is stationary and other is moving with ...
0
votes
3answers
84 views

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 ...
0
votes
2answers
179 views

Special Relativity and Gravity

As Einstein was seeking a relativistic theory of gravity, he thought that special relativity should be upgraded to general relativity thus promoting the Minkowski space to curved pseudo-Riemannian ...
0
votes
1answer
86 views

Question regarding FTL information transfer between two inertial frames

Why can’t information travel faster than the speed of light, if the two endpoints to and from which the information is being sent are moving relatively to each other, as long as the information ...
0
votes
2answers
144 views

Relativistic Time Difference

I thought that it might be interesting to calculate the time difference between a clock placed on Earth when I was born and a hypothetical clock placed at the centre of the sun at the same time. I ...
0
votes
1answer
43 views

The elevator and the bolt [closed]

I had this question, I don't seem to get what I am doing wrong so here it goes:An elevator car whose floor to ceiling distance is equal to $2.7 m $ starts ascending with a constant acceleration of ...
0
votes
2answers
40 views

When e/m varies with velocity, charge is variable

It is found that the e/m ratio of an electron varies with velocity. Current physics assumes that it is mass that is variable with speed. Is there any fundamental reason why it cannot be assumed that ...
0
votes
3answers
89 views

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?
0
votes
1answer
46 views

Is the matrix representation of the Lorentz transform the same for all 4-vectors?

If I have a four vector of the form: $$ \left( \begin{array}{ccc} T\\ \vec{X}\end{array} \right) $$ where $T$ is the analogous time component (i.e. energy, angular frequency, scalar potential, charge ...
0
votes
1answer
63 views

Spacelike interval and length contraction

I am having a serious trouble finding an agreement between the two facts in Special Relativity: (1) given two events $A$ and $B$ in spacetime separeted by a spacelike interval $s$, the distance in ...
0
votes
4answers
182 views

Can you tell your absolute speed in space?

Normally in relativity your speed can only be known relative to another object, given that as one approaches light speed more energy is required to accelerate faster, based on the energy consumption ...
0
votes
3answers
124 views

What is the pace of absolute time

How fast or slow compared to my alarm clock time does time passes in a place where there is no gravitational pull and where you are not moving. I don't know if my question is clear, but is there some ...
0
votes
1answer
456 views

what if an object moves with speed of light,does it converts into energy or mass?

If a mass is moving with speed of light does it converts into energy of remains as mass it self?As per relativity theory if a mass moves with speeds comparable to speed of light then the time on the ...
0
votes
2answers
134 views

For a rocket travelling to a planet, which reference frame measures the dilated time?

I'm getting into some confusion with relativity. Consider a rocket and the Earth as two observers, and then the rocket travels to a distant star. Is the proper time taken measured in the frame of ...
0
votes
4answers
295 views

Expected result of vertical Michelson-Morley Experiment [duplicate]

What would the result of a vertical variation of the Michelson-Morley experiment be? I.e., if one were to compare light traveling along a horizontal arm with light traveling along a vertical arm ...
0
votes
2answers
441 views

What happened to potential energy?

I was learning how charge can be virtue of a body's potential energy.Meanwhile,I was hung by this question. [gravitational and other forces except coulombic,are assumed to be not acting on the ...
0
votes
1answer
79 views

gamma-gamma collision seen from a relativistic rocket

This is a thought experiment. Consider two photons traveling at right angles and intersecting at some point. As seen from Earth these photons will not interact with each other because their energy is ...
0
votes
2answers
281 views

light travels a maximum speed… /? [duplicate]

Possible Duplicate: Is it possible for information to be transmitted faster than light? we know that speed of light is an unconquerable term in physics..light takes about 1 year to travel ...
0
votes
2answers
370 views

The Lorentz Transformations in the Micro-World

Two particles[or micro-observers] A and B are in relative uniform motion wrt each other in the x-x’ direction. The “observer” A decides to deduce[or interpret] the Lorentz Transformations wrt to B. ...
0
votes
1answer
43 views

Relativistic Electrodynamics [closed]

What are the applications of relativistic electrodynamics I've been learning about it in a theoretical physics module however I don't understand what implications or uses it has in real life and ...
0
votes
1answer
36 views

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 ...
0
votes
1answer
54 views

When travelling in the direction of light, what is my relative velocity?

If suppose I am traveling in the same direction as that of light, the relative velocity I am traveling with is speed of light + my speed in the direction of light. Is this correct? Does this have ...
0
votes
1answer
55 views

Magnetic field existence - a relativistic approach

Recently I learnt that magnetic force is equal to relativistic electrostatic force. With this approach I was able to understand the motion of a charged particle kept near a current carrying conductor. ...
0
votes
1answer
78 views

How to prove that “all unaccelerated frames behave likely for all isolated bodies”? [closed]

Say in an unaccelerated frame "S" a "isolated body A" moves with constancy of velocity , can we predict mathematically that any other such body B will move with same velocity in that frame.... My ...
0
votes
2answers
56 views

Time dilation and reference frame in an orbiting context [closed]

I have looked for other answers, but most confused me more than clarified and did not provide specific calculations. So I am still struggling with this simple question. Consider two persons, $P_a$ ...
0
votes
3answers
176 views

Are there any well-known large body objects moving at a significant fraction of the speed of light relative to earth?

Introduction I've been reading a book called PsychoPhysics, part of the "Illuminati God Series" by Mike Hockney (a pseudonym). Without getting into too much detail, they basically believe that the ...
0
votes
1answer
96 views

Black Holes and Einstein Field Equations

I recently watched a video where Michio Kaku argues that there must be something fundamentally wrong with the theory of General Relativity because it gives time t=0 as a solution at the centre of a ...
0
votes
2answers
166 views

Why does gravity affect time?

So Special Relativity states that for all non-accelerating objects of matter the laws of physics are the same. I'm confused on why this law of physic applies to objects in acceleration and gravity ...
0
votes
1answer
82 views

Dirichlet boundary conditions in space-time?

In the context of string theory, and world sheets the Dirichlet boundary conditions can be written as: $$\frac{\partial X^\mu(\tau,\sigma_1)}{\partial \tau}=0$$ where $\sigma_1$ is the value of the ...