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3

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 ...

5

I don't think I can rigorously prove that simulation engines don't need to worry about the (possibly? I don't know if there's a reliable measurement) finite speed of gravity, but I can offer some lines of thought that point in that direction. I'll start with your question 3. Suppose that gravity does have finite speed equal to $c$. Your question seems to be ...

7

It's tempting to think of gravity as some kind of interaction between the two bodies involved - maybe some form of signal (gravity wave?) sent between the two bodies. If this were the case then you would indeed have to allow for a propagation delay as the signals were sent between the two bodies. However this is not how gravity works. A massive object ...

0

In Special Relativity CTCs can't exist (or at least I don't think so) but General Relativity has solutions that include CTCs. The best known is probably Gödel's solution for a rotating universe. The Alcubierre drive could also be used to construct CTCs, as could any FTL mechanism. Also see the Tipler cylinder, and probably many other examples I can't ...

0

I think I got answer myself. The vanish commutator and EPR paradox are not correlated. The vanishing commutator simply says, once a measurement at $x$ was done, the obtained state will not bring uncertainty for measurement of $y$, by the simutaneous eigenstate property. Not like one measures momentum, the state becomes $|p \rangle$, then measure position ...

1

The statement is a consequence rather than an assumption. It is limiting the domain of event pairs to those which can be considered causally connected. In a sense it is requiring that there be the possibility that the event A be detectable in the future of event B if it is to be considered causal. The light-cone from event A defines the boundary of that ...

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 $B$") ...

4

Causality is preserved, unless Tachyons exist. Part 1: STR doesn't assume causality. Causality is violated when you have a flow of information that goes back to the same place in space AND time, creating a contradiction. Both newtonian and STR guarantee causality. STR is more complex, but it still prevents anything from going back in time with respect to ...

2

I would have liked to comment but you need 50 reputation. I think that your thought experiment is set up incorrectly. Yes in other inertial reference frames two events will not be simultaneous. However, $C$ is stationary within its own reference frame including the simultaneous events. Thus, $C$ will occur regardless of what other reference frames see.

-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 ...

0

Yes, as you say, there is a built-in time symmetry in the mechanical laws that underlie our universe. At the moment the most accurate statement seems to be CPT symmetry. Under a CPT reversal (particles -> antiparticles, flip space, flip time), mechanics works identically. On a practical level though, even time symmetry alone holds to a good degree. It is of ...

0

Full reversibility at the elementary level does not imply what you suggest: new qualitative features appear as the scale of the system and its ability to interact with the rest of the world increase, so that dissipation (irreversibility, loss of "useful" energy) at the level of our everyday experience does not contraddict microscopic reversibility. If a ...

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