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8

You're quite correct that measuring time from the Big Bang does separate spacetime into a time bit and a space bit, but this isn't arbitrary. When we want to describe the universe around us we need to choose some coordinate system that we can use to record physical quantities. Whatever coordinate system we choose will have one coordinate that behaves like ...


6

While DanielSank's answer is correct, I don't think it is the complete story. Sure the equivalence principle naturally leads to a geometric description of gravity but it does not necessitate such a description in and of itself. For example, Newtonian gravity can be described geometrically in a manner completely analogous to GR but at the same time this ...


5

As Einstein himself put it, "If a person falls freely he will not feel his own weight." Consider yoruself sitting in your chair right now. You don't see to be accelerating, yet you feel a force on your butt. This is very strange because $F=ma$$^{[a]}$ would suggest that if you are under the influence of a force (the one on your butt) you should be ...


2

Gravity, like all cause-effect relationships, propagates at a maximum speed of $c$; indeed from the Einstein field equations small amplitude (linear limit) gravitational waves travel at precisely $c$. A good idea for what is going on comes from an approximation of General Relativity called Gravitoelectromagnetism. This makes an approximate analogy between ...


2

This seems to be a simple matter of confusion regarding which variables are held constant. His notation $$\frac{\partial X}{\partial\tau}(\tau,\sigma_*)=0$$ is misleading. What he really means is $$\frac{\partial}{\partial\tau}\left(X(\sigma_*)\right)(\tau)=0$$ In other words, we fix $\sigma$ to be one of the end points and look at how it changes with ...


2

Let's say its moving roughly 32,500 mph or about 16.316 km/s relative to the Earth. If we consider special relativity then we have ten years of seconds divided by the square root of one minus 16 kilometers per second squared over the speed of light squared. The answer turns out to be roughly half a second!


2

Is there an absolute pace of time, no. Is your clock , in a region without gravity, (and at "rest" relative to other objects) "ticking" faster than your alarm clock on the Earth's surface, yes. But obviously you physically cannot escape the effect of gravity, no matter how far away the mass-energy sources are, so this will vary from observer to observer, ...


1

There isn't a such thing as "absolute time." Some events – they are called space-like events – can't even be agreed to happen in an "objective order." Only time-like events can be universally agreed to happen in a particular order, but there's no such thing as "universal time." For you, time will always tick per one second by second, and that will apply to ...


1

General relativity is not a replacement of special relativity because the latter fails with gravity, rather it is the extension of its kinematic and dynamical quantities to accelerated systems, which, in turn, correspond to writing down the same equations of motion but with a different (non-Euclidean) metric. Why then accelerated systems are equivalent to ...


1

Absolute zero corresponds to the theoretical state in which particles have no energy at all. Absolute zero is the point where where all molecules have no kinetic energy. It is a theoretical value (it has never been reached). I think you are mixing up total energy with kinetic energy, (and ignoring rest energy) then using E = mc$^2$ to conclude that ...



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