# Tag Info

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In Special Theory of Relativity, all inertial reference frames are able to communicate with each other to share their results. And, they all agree with the value of c and related conclusions. In General Theory of Relativity, it's not always true. There are situations when two inertial reference frames may not be able to communicate with each other. In such ...

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In SR, there are global inertial reference frames and, in this context, no object moving with speed less than c in one reference frame moves with speed equal to or greater than c in any reference frame. But, in GR, in a curved spacetime, there are no global inertial reference frames. Instead, there are local inertial reference frames. We say ...

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The truth is, light speed isn't necessarily the fastest thing there is. If you went into your backyard and pointed a laser at one edge of the moon, and then moved it quickly to the other edge of the moon, your laser point on the moon would by moving on the moons surface faster than the speed of light. However, nothing that is not completely composed of ...

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A better way to think of it would be that space is being added to the universe; the universe is not "moving". Consider the case of two stars. The expansion of the universe doesn't cause the stars to "move" away from each other. Rather, space is created between the stars, resulting in them being further apart. This consequently, doesn't violate general ...

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The universe is not expanding faster than the speed of light. Red shift data from the most distant galaxies do not support this premise. Fact is, E=mc^2 is still the most used relation in physics, and it's Einstein's. This relation was derived assuming (as a postulate) that the speed of light to be both maximal and independent of the inertial reference ...

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Both neutrinos and anti-neutrinos are affected by gravity (same magnitudes and direction). The 1987 Supernova event was the first instance of neutrino and anti-neutrino detection of a source outside of our solar system. Not only were they detected, but the neutrino event recorded occurred a short interval of time AFTER the visible light and gamma ray burst ...

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The idea that the pendulum would drop instantly isn't even true of short, Earth-bound pendula: c.f. various Internet videos about dropping slinkies (toy springs). The reason why slinkies drop in this way is essentially the same reason why an idealised pendulum (strong enough to hold itself together, albeit maybe not as stretchy as a slinky) would not ...

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The mass $m$ in the formula is NOT the rest mass $m_0$ and therefore dependent on the velocity: $$m = \frac{m_0}{\sqrt{1-\frac{v^2}{c^2}}} \equiv \gamma m_0$$ This means you cannot simply take the normal mass of a nitrogen atom and put it in there, if you assume a speed $v \neq 0$. The $c$ in the formula doesn't mean that the particle travels at light ...

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Your calculation is wrong because $E=mc^2$ doesn't mean that the object has velocity $c$. To make my answer useful i will give a very brief overview of Dynamics at higher velocities which is a consequence of Special theory of relativity. At higher speeds(of order of $c$) Newtonian mechanics is not valid. The linear momentum is defined as: $$\vec p=m_0\gamma ... 2 The flaw in your argument is that the claim "entanglement will instantly replicate the photons' paths and such the pattern onto Bob's screen [sic]" is incorrect. The statistics for the measurement outcomes of any experiment performed on one subsystem of a maximally entangled pair is independent of what goes on with the other subsystem. In your case, from ... 4 The problem with this sort of scheme is that Alice has no control over the results of her measurements, since those are random. This means that she can control which basis Bob's spin is projected on, but she cannot control which of the basis states gets chosen. Bob will then see a random mix of results which turns out to contain no trace of what Alice was ... 4 Your error seems to be the misconception that entanglement will magically make the results of any experiment of photon B exactly mimic those of a similar experiment done on its entangled partner. Entanglement is more subtle than that and must be treated carefully. In particular, there are many different types of entanglement. For example, photons may be ... 0 I've heard that a spacecraft could never exceed the speed of light because it's (relativistic) mass quickly approaches infinity and therefore there could never create a big enough rocket to propel it faster and faster. In fact, the spacecraft could never even reach, much less exceed the speed of light. I think that you'll agree that the ... 1 The problem is- The rocket is not 'fighting' with any force-field, it is 'fighting' with the very nature of space-time. So unless we have something of zero rest mass 'things' will tend to infinity. And yes the thrust will increase but space-time will distort( following Lorentz transformation, no GR effect here) in such a way that reaching 'c' 'tests' our ... 0 The two postulates of STR doesn't say that any signal cannot move faster than light. This superficial appearance is deceiving. After all, the postulates involve notions such as inertial frame and speed; therefore they require and presume definitions of how to measure whether or not two participants (such as a "sender A" and a "receiver B") ... -2 we cant track a signal moving with a velocity more than C.we can say that it will not interfere with the material matter.it can pass through any matter with out making a interaction with it as it will pass through the matter as of its momentum hf/c2*infinity in this instance which is very high. even though it passes through it the body will be perfectly ... 1 The important thing is that all speeds seem to change: If you would look at the universe, in this case the two protons, from the perception of a man shrunk to the size of a proton, not only would the particles appear much faster, but so would the speed of light. So if you shrunk yourself to a trillionth of what you are now, one proton would have a diameter ... 3 If I understand you correctly, your two points about apparent slowness of speeds is related to scale, and disappears when you quantify it using a common unit. ie: We think of 10m/s as relatively slow because the average human is 1.8 metres in height, and we can imagine that 10 metres per second, or 36 kilometer/hour as an achievable speed using a machine ... 0 A "vertical variation of modern versions of the Michelson-Morley experiment (MMX) with one arm pointed in the vertical direction" experiment has been performed. Watch the following video starting at 0:45. http://youtube.com/watch?v=s9ITt44-EHE "Imagine the Earth as if it were immersed in honey," says Francis Everitt of Stanford University in California, ... 1 String theories respect symmetries of the 4d Poincare group, including those that result in special relativity. As such, faster than light particles are expected to be absent in nature, if string theory is correct. 0 No, even if no particle does the entire trip, the pole has elastic properties, i.e., you push some molecules, and those push the next ones, and so on, until the information that travels with the pushes reaches the other side. You're basically sending a density wave through the pole. This video of a falling slinky in slow motion shows that. -2 There's no answer to this "Why". This is what we observe in nature. Nothing* can travel faster than light. *Note: Denizens of the Quantum World like atom may not be agree with this. For example, information of quantum states of two entangled entities are shared between them faster than light. It has been tested with polarized light beams. Understand it this ... -5 Because not until now that scientists discovered laws that can be applied on objects attaining even the speed of light .. actually no one knows what happens when an object attains the speed of light 0 I'm going to take a slightly different approach to explaining this, in analogy with a great answer about the ontological nature of Newton's Laws. First, let's posit the existence of an inertial reference frame. It doesn't matter which one, but there has to be one. This is an important point, and one that's often overlooked. In it, nothing is moving faster ... 1 You have to measure everything from the same frame of reference. Your own frame of reference obviously has a velocity of 0, relative to you. The other object moving toward you, or away from you, will never move faster than the speed of light as seen from your frame of reference. A third observer can see two objects, each moving at the speed of light. Toward ... 0 The short answer has been given a few times in the comments: gravity only bends light, it doesn't speed it up. Of course this statement in and of itself is useless if you want to understand nature. So let's dig a bit deeper. To understand why gravity acts this way, the first step is the equivalence principle. Now, there are several versions of this but we'll ... 5 If a ray of light is aimed exactly at the center of a body, then will it get accelerated like a meteor? Short answer: no. However, when falling in a gravity field, the momentum of light increases. Some background... In Newtonian mechanics, the rate of change of momentum of a (massive) particle is proportional to the acceleration:$$\frac{d\vec ...

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