Tagged Questions
0
votes
3answers
104 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 ...
3
votes
3answers
315 views
Why do clocks measure arc-length?
Apologies in advance for the long question.
My understanding is that in GR, massive observers move along timelike curves $x^\mu(\lambda)$, and if an observer moves from point $x^\mu(\lambda_a)$ to ...
1
vote
1answer
139 views
Why is energy-momentum 4-vector so much easier to explore/observe than spacetime 4-vector
I have read that spacetime 4-vector is quite difficult to observe/explore and that energy-momentum 4-vector is much more appropriate for CERN etc.
Why is that? Could anyone give me a brief ...
0
votes
0answers
126 views
What facts and examples should I use in a debate with a Relativity Denier? [closed]
I have been asked to 'defend Science' at a Creationist event in Minneapolis, MN, and the guy I'll be debating is against 'Einsteinian Relativity', or as he characterizes it, the idea that there is no ...
3
votes
3answers
143 views
Having trouble seeing the similarity between these two energy-momentum tensors
Leonard Suskind gives the following formulation of the energy-momentum tensor in his Stanford lectures on GR (#10, I believe):
$$T_{\mu \nu}=\partial_{\mu}\phi \partial_{\nu}\phi-\frac{1}{2}g_{\mu ...
2
votes
0answers
118 views
How do I extend the Lorentz transformation metric to dimensions>4?
How do I extend the general Lorentz transformation matrix (not just a boost along an axis, but in directions where the dx1/dt, dx2/dt, dx3/dt, components are all not zero. For eg. as on the Wikipedia ...
0
votes
2answers
166 views
length contraction question
we know from eintein's theory of relativity that lets say, a ruler is travelling to a speed if light, then we can say that the ruler (from our view as observers) has shorten. but why, lets say we have ...
2
votes
2answers
165 views
Using Einstein's Relativity: Who is younger?
Suppose we have a person A and a person B.
Person B travels very close to speed of light and never returns. He's constant in speed. Then, we can say two things:
B is younger than A.
A is younger ...
5
votes
2answers
480 views
Is this a quaternion Lorentz Boost?
The quaternion Lorentz boost $v'=hvh^*+ 1/2( (hhv)^*-(h^*h^*v)^*)$ where $h$ is $(\cosh(x),\sinh(x),0,0)$ was derived by substituting the hyperbolic sine and cosine for the sine and cosine in the ...
6
votes
2answers
302 views
Do Lorentz Boosts in the same direction form a group?
I know that two consecutive Lorentz Boosts in different directions produce a rotation and therefore Lorentz Boosts don't form a group. But, my intuition tells me that, Lorentz Boosts in the same ...
11
votes
4answers
380 views
Is there an easy way to show that $x^2-t^2=1/g^2$ for a (relativistic) body undergoing acceleration g?
A professor asked me about the (c=1) equation:
$$x^2 - t^2 = 1/g^2$$
which I used in a paper. Or with $c$:
$$x^2 - (ct)^2 = c^4/g^2.$$
I told him that it was the exact equation of motion for a ...
4
votes
2answers
908 views
How to deduce the theorem of addition of velocities?
Lorentz contraction and time dilatation can be deduced without Lorentz transformation. Can you deduce also the theorem of addition of velocities
$$w~=~\dfrac{u+v}{1+uv/c^2}$$
without Lorentz ...
4
votes
2answers
682 views
How can time be relative?
I don't understand how time can be relative to different observers, and I think my confusion is around how I understand what time is.
I have always been told (and thought) that time is basically a ...
11
votes
2answers
611 views
A simple pendulum moving at a relativistic speed - how does the period change?
I've been pondering the precise mechanism of time dilation for the example of a simple pendulum in two different situations:
The observer and ground are at rest in one frame of reference; the ...
4
votes
3answers
795 views
Is acceleration relative?
A while back in my Dynamics & Relativity lectures my lecturer mentioned that an object need not be accelerating relative to anything - he said it makes sense for an object to just be accelerating. ...
2
votes
1answer
213 views
Thought experiment about acceleration
Case 1: two people wake up in spaceships accelerating at 1g. They can measure or observe anything inside the room but not outside. They couldn't determine if they were on a spaceship or on earth. ...
0
votes
0answers
38 views
Why has the ether been disregarded as a valid medium through which light can propagate? [duplicate]
Possible Duplicate:
Ether theory acceptance
Although the Einstein's theory of relativity seemed to make the concept of an ether obsolete, did it necessarily invalidate it? Are there any ...
1
vote
4answers
269 views
Is there a universal rest frame of reference?
I am still struggling with C being a constant and what that implies.
So can an experiment be done to find the resting state for the universe?
Take a device with an observer and a light source and two ...
-2
votes
2answers
126 views
frames of reference [duplicate]
Possible Duplicate:
Help Me Gain an Intuitive Understanding of Lorentz Contraction
Frames k and k' are inertial frames. Frame k' is moving at a velocity of magnitude v relative to frame k ...
0
votes
2answers
148 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 ...
2
votes
4answers
328 views
Reducing General Relativity to Special Relativity in limiting case
I understand that general relativity is applicable to gravitational fields and special relativity is applicable to case when there is no gravity. But is there a derivation on how to reduce General ...
1
vote
2answers
138 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.
6
votes
7answers
1k views
How does Newtonian gravitation conflict with special relativity?
In the Wikipedia article Classical Field Theory (Gravitation), it says
After Newtonian gravitation was found to be inconsistent with special relativity, . . .
I don't see how Newtonian ...
1
vote
2answers
275 views
Where does the minus sign appear from in the metric tensor?
Trying to understand Schutz's AFCIGR, where does the minus sign appear from in the metric tensor?
I understand that this expresses the invariance of the spacetime interval. Schutz says (I think) ...
2
votes
3answers
1k views
Difference between timelike and spacelike vectors
Other than one having a positive invariant scalar product and the other a negative one, what are the actual physical differences between these vectors?
2
votes
1answer
332 views
How will the Twin Paradox become, for Time Dilation, if no acceleration was ever involved?
I think one catch in Twin Paradox was about the big acceleration that can turn back the traveling twin from light speed outward bound, to become light speed inward bound.
What if there is strictly no ...
5
votes
2answers
199 views
Why absoluteness of time implies galilean transformations?
In Landau course, vol.1 Mechanics, one finds the statement: "...the absoluteness of time necessarily implies that the ordinary law of composition of velocities is applicable to all phenomena."
I ...
4
votes
5answers
513 views
Time Dilation - How does it know which Frame of Reference to age slower?
Okay, I'm asking a question similar to this one here: Time Dilation - what happens when you bring the observers back together?. Specifically, I am curious about a specific angle on the second part of ...
8
votes
3answers
570 views
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 ...
