Time is defined operationally to be that which is measured by clocks. The SI unit of time is the second, which is defined to be
4
votes
1answer
66 views
Could a bipolar nebula be produced by a time gradient?
M2-9 is an example of a bipolar nebula that resembles two back-to-back rocket nozzles. Is it possible that this shape (somewhat unusual for an explosion) is the result of a time gradient? A rotating ...
1
vote
4answers
143 views
What is the exact mechanism by which time dilates?
What is the exact mechanism by which time dilates for a fast moving object?
Can the time dilation be explained by any theory other than relativity?
0
votes
0answers
34 views
Time ordering and Fermions
Having time ordering operator for fermions, should it reverse sign if it swaps operators with opposite spin variable? In other words should
$T[c_{t_1,\uparrow}c_{t_2,\downarrow}^\dagger]$
return ...
6
votes
1answer
93 views
Cancelling special & general relativistic effects
We know that for a GPS we need to make a correction for both general and special relativity: general relativity predicts that clocks go slower in a higher gravitational field (the clock aboard a GPS ...
-4
votes
2answers
99 views
Is this a great flaw in big bang theory? [duplicate]
Einstein said that, Time & Space cannot exists without one another. Big bang says, time didn't exist before the big bang. So the Primordial ball referred in the Big Bang theory didn't had any ...
0
votes
1answer
72 views
Did space and time exist before the Big Bang? [duplicate]
I accept the Big Bang theory. What I can't understand is how there can be a where or when to the Big Bang if space time did not exist prior to it. Did space and time exist prior to the Big Bang?
14
votes
4answers
1k views
How is the classical twin paradox resolved?
I read a lot about the classical twin paradox recently. What confuses me is that some authors claim that it can be resolved within SRT, others say that you need GRT. Now, what is true (and why)?
1
vote
1answer
21 views
Are “timed” measurements actually revealing error-distributions of the measurement apparati?
A thought experiment:
Given some object moving (swinging) from left to right and back with constant velocity, imagine a camera set up to take a picture of the scene at a fixed interval so that we can ...
1
vote
0answers
58 views
General physics question involving Heisenberg Uncertainty Principle
Question:
An unstable particle produced in a high-energy collision is measured to have an energy of $483\ \mathrm{MeV}$ and an uncertainty in energy of $84\ \mathrm{keV}$. Use the Heisenberg ...
6
votes
5answers
355 views
More than one time dimension
We know that space-time dimensions are 3+1 macroscopically, but what if 2+2?
Obviously it is tough to imagine two time dimensions, but mathematically we can always imagine as either having two ...
2
votes
4answers
192 views
Time inside a Black hole
If time stops inside a black hole, due to gravitational time dilation, how can it's life end after a very long time? If time doesn't pass inside a black hole, then an event to occur inside a black ...
2
votes
1answer
216 views
When is the right ascension of the mean sun 0?
I understand that the right ascension of the mean sun changes (at least over a specified period) by a constant rate, but where is it zero? I had naively assumed that it would be zero at the most ...
2
votes
1answer
37 views
Need help with the position of a particle in a velocity-versus-time graph
I am having trouble with a velocity-versus-time graph. I recently took a Physics test that asked this question: The graph shows the velocity versus time for a particle moving along the $x$ axis. The ...
4
votes
1answer
89 views
Does the collapse of the wave function increase entropy of the atomic system itself?
Does wave-function collapse cause the entropy of the atom (ie. the sub-atomic particle system that makes up the atom) to increase?
2
votes
1answer
762 views
Anti-matter black hole and time
I have recently read some hard science-fiction story based on an assumption that if time stops (from external observer's perspective) on the event horizon of black hole, then in an anti-matter black ...