Tag Info

New answers tagged

0

The truth of the Lorentz transformation as an accurate description of the co-ordinate transformation between relatively uniformly moving observers needfully implies relativity of simultaneity. Contrapositively, the Lorentz transformation cannot be sound if simulteneity is not relative. So, in the sense that the soundness of the Lorentz transformation has a ...


1

If you and your friends took some helicopters to the north pole and went up and then took off in different directions and flew at the same altitude you would feel like you were being bent towards each other, but yet as you all started to approach the south pole you would notice that you were all moving a way from other at first, you were all moving parallel ...


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 ...


0

I go with Time is the separation between distinct events that happen in the same place. which is very general and not quantitative at all, but covers the basics. Given three distinct events that happen at the same place we can determine which happened between the other from just the values of the three separations. And it agrees with the notion that ...


0

The 7 fundamental quantities are hard to define. Time Displacement/position Mass Temperature Current Amount of substance (e.i. the mole) Luminous intensity More here: http://gravimotion.info/Physics_seven_basic_quantities.php Time is just one of them. If someone asked me, I would say something like "Time is how long something lasts" or "Time is the ...


-3

Is it true to say that all matter in the universe is travelling with velocity c through spacetime? Actually, no. Because there is no motion through spacetime. Spacetime models motion through space over time, but because it includes the time dimension, it's totally static. And whilst this model works very well, we live in a world of space and motion, ...


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!


0

I'd like to add a few words to Domagoj Pandža's excellent answer. He makes this statement: "....Intuition and perception (or the lack of there of) can be a big problem when you're trying to comprehend the implications of special/general relativity ...." I think Domagoj's answer is excellent, but I disagree a little with this statement. Actually almost ...


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

I think physically it is very clear. If the string endpoint ($\sigma=\sigma_1$) is fixed, the variations must vanish there i.e. $\delta X(\tau,\sigma_1)=0$.


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 ...


0

Temperature is related to the kinetic energy of harmonic oscillators associated with the degrees of freedom in the medium. In a gas, there are degrees of freedom for translation (i.e. velocity) of the particles, and also rotation if the particles are not monatomic. Thermal energy is partitioned equally between translation (i.e. velocity) in the x, y, and z ...


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 ...


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 ...


0

So, here's the deal. "Time is relative" means a lot of different things to a lot of different people. In order to make a solid step forward, Einstein and company basically needed to clarify what they were trying to say. What they were trying to say looks something like this: "if you see a train passing by you, you're going to see things happen in slightly ...


-4

If you think about it, time as we know it does not actually exist/flow - it is our mental manifestations of the world around us that we think of as time. For example, what we see is not actually there as we view it. The object sends us light-waves (only a small portion possibily of what the object really is), our eyes then have to decode the light waves and ...



Top 50 recent answers are included