# Tag Info

0

Yes, because what slows down clocks is acceleration, whether by gravity or by centrifuge, if you like. It doesn't matter how fast the airplane is, but how high it is, because gravity is stronger at lower elevations.

1

What you read is correct. I am not sure if those were the exact words of your teacher but according to the general theory of relativity, sun doesn't "attract" the photon (or any other body for that matter). In fact gravity is not even a real force. Let me briefly state what the theory of relativity has to say about gravity without going into the complicated ...

5

To properly understand what is going on you need to understand general relativity. Massless particles, like photons, travel on null geodesics and mass bends spacetime so the null geodesics are not straight lines. The problem is that neither you nor your teacher understand general relativity so this isn't a very convincing argument. But here is an argument to ...

1

In Feynamn lectures, he shows in a rather straight-forward manner, taking the example of a charge moving parallel to a wire, that a complete electromagnetic description is invariant to the inertial frame of reference, i.e. electricity and magnetism taken together are consistent with Einstein’s relativity. So in cases, such as your example, you must always ...

3

The unified formula used in General Relativity is $$d\tau=\sqrt{\sum_{\mu=0}^3\sum_{\nu=0}^3 g_{\mu\nu}dx^\mu dx^\nu},$$ which by Einstein's notation (summation over doubly repeating indices is implicit) is also written as $$d\tau=\sqrt{g_{\mu\nu}dx^\mu dx^\nu}.$$ Here $d\tau$ is the proper time "felt" or measured by particle moving in the spacetime, for ...

2

The time dilation due to velocity and due to spacetime curvature can't be separated. Both are derived from the metric. There isn't a general formula for this because it depends on the metric in question. For example in my answer to the question A clock in freefall I calculate the time dilation for an observer falling from infinity towards a black hole, but ...

1

It's a perfectly valid interpretation. If you have a look at the question How long would it take me to travel to a distant star? you'll find it's quite possible to cover a distance greater than $ct$ in an elapsed time $t$. But this doesn't mean special relativity is wrong - indeed the calculations done in that Q/A were done using special relativity. The ...

0

One can in principle travel a given distance along a ruler in arbitrary short time. The relevant velocity definition is proper velocity: the distance measured by an observer at rest with respect to the ruler, divided by the time passing on the wristwatch of the traveller. Note that proper velocity deploys a mixture of reference frames, whereas ordinary ...

1

There is geometrical significance. You are sooo close. You are in Euclidean space, but you should be in hyperbolic space. As @fqq points out, you have stumbled upon rapidity, a parameter in hyperbolic geometry that is the analog of angle in Euclidean geometry. In Euclidean geometry an angle (in radians) is a parameter that measures the Euclidean length ...

1

Rather than rehash the equations which have been referenced already, I wanted to first cover the Michelson-Morley experiment. Michelson, Morley and even Lorentz were actually able to do a considerable amount of work on the prediction of the expected existence of the aether wind. The foundations of the underlying equations where strong by this point. The ...

0

i would say the intuition is the simple observation (by Einstein, Lorentz, Poincare and others) of these 2 things: Velocity of light ($c$) is $c$-onstant accross interial frames (extrapolated result from Maxwell-Lorentz equations) The velocity of light ($c$) is an upper limit on every other velocity a material body or signal can achieve (in effect $c$ ...

0

This is how you derive the equation for time dilation. The metric used in special relativity is the Minkowski metric: $$ds^2 = -c^2dt^2 + dx^2 + dy^2 + dz^2$$ and the basic principle of special relativity is the the line element $ds$ is an invariant, that is all observers in all inertial frames will measure it to have the same value. Suppose we are ...

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To me personally, the most intuitive way of understanding SRT is to always keep in mind that, in SRT, the interval $$ds^2=-c^2dt^2+dx^2=-c^2d\tau^2$$ has to be invariant. From this simple formula, everything seems to flow naturally. In particular, it is easy to see the form of the Lorentz factor arise from here, by using $\frac{dx}{dt}=v\to dx=vdt$. Using ...

3

If we assume (1) the 'stick' (rod) does not contract according to an observer fixed at any point on the rod and (2) any point on the rod has constant proper acceleration and (3) the rod is momentarily at rest at $t=0$ in some inertial frame of reference then every point on the rod is a Rindler observer which means that every point on the rod has a ...

3

You're correct that different parts of the object have to accelerate differently. The details are pretty complicated—when you push one end of an object, transient pressure waves bounce around inside it, and it eventually settles down into a new equilibrium state, which happens to be moving and (in the original reference frame) shorter than before. A simpler ...

-1

This is a question that is asked the world over and the answer seems obvious to me, yet everyone deems it to be from perception which for me seems to be the issue apply some 1st grade logic to the situation and the answers reveal themselves quite simply. For instance, travelling faster than light from a single point of perception this is absolutely possible ...

0

Your question exposes the importance of defining notions in physics unambiguously and universally in terms of "How to measure?". As Einstein put it explicitly (however, referring specificly only to the notion of "simultaneity", and unfortunately only as late as 1917): "We thus require a definition of simultaneity such that this definition supplies us with ...

2

For Special Relativity (SR) i think the Michelson-Morley experiment is compatible and provides a verification of SR principle (some other formulations are also compatible with the experiment). Quantum Field Theory and especially the Dirac prediction and verification of positron is also a verification of SR (and many other expreriments in this context) For ...

2

Let's ignore gravitational time time dilation for now to keep things simple. Suppose we place me and a second clock 300km (the altitude of the ISS orbit) above the Kansas clock, and by some means we hover there so we are stationary with respect to the Kansas clock. That means both clocks are in the same inertial frame so they run at the same rate and will ...

2

No, Einstein's relativity hasn't been proved wrong by anyone up to now. Anyone who did would get a Nobel Prize.

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