# Tag Info

8

The answer to (2) is simply that no-one knows, and further that it's unlikely we will ever know. It's impossible to prove that the universe is infinite, but it's just possible we might prove it closed and therefore finite if the length scale is around the size of the currently observable universe. The paper Topology of the Universe: Theory and Observations ...

5

Assuming you're willing to accept General Relativity as a valid theory, your question has a well defined answer because we can solve the equations of GR for an empty universe. The result (well, the simplest result) is Minkowski spacetime. You might think that nothing much can happen in an empty universe, but even though no matter or energy is present there ...

4

Isn't dt something that cannot change? In Special Relativity, time $t$ is a coordinate rather than a (universal) parameter. To locate an event in spacetime in a particular reference frame, one must specify 4 coordinates, 3 spatial and 1 temporal. So, a quantity like $\frac{dx}{dt}$ is a coordinate velocity; it is the rate of change of one coordinate ...

3

I don't see your problem. We are dealing in hypothetical situations that lead to paradoxes and inconsistencies, so there is no problem with postulating what would happen if...?, even if the "if..." is impossible. He could have as easily said what would happen if the sun moved suddenly, we would see it move after 8 minutes, but gravitationally feel it move ...

2

You are right that there are two effects at play here. Firstly, suppose that we turn relativity off --- suppose that we consider our universe to be Newtonian, with a finite speed of light propagation. It would indeed be the case that if an observer A were moving relative to another observer B, and emitting a light signal towards B, then the rate at which ...

2

People defined time as a variable going forward long before entropy was defined. Biological/consciousness time, which you also discuss, forced the concept of time and a way /unit to measure it, as cultivation and buildings forced a concept of space and units to measure it. The celestial clock of sun moon and planets was used even by primitive people. ...

2

As the comments say, you have to be precise about your reference point when you talk about time dilation. Time dilation is always relative to something else. But there is an obvious interpretation to your question. Suppose you have an observer well outside the Solar system and stationary with respect to the Sun. For that observer your clock on Earth is ...

2

Similar questions have cropped up on this site many times, and the debate surrounding them is usually fractious because people misunderstand each other's use of words like exist. One of the lessons of General Relativity is that any observer has to choose a locally convenient coordinate system that may not be globally convenient. We on Earth (quite sensibly) ...

1

Yes, if you lived in space far from the Solar System you would think slightly faster than you do on Earth. However the connection to velocity is a red herring. As Alfred says in his comment, you're at rest in your own rest frame so you're already thinking as fast as you can. Re your Q2: the fastest speeds regularly experienced by humans (airplane flights?) ...

1

The equation for time dilation is $$\Delta t =\frac{\Delta t_{0}}{\sqrt{1-\frac{v^2}{c^2}}}=\Delta t_{0}\gamma$$ Where $\Delta t$ is the time that passes for the moving observer (according to the stationary observer), $\Delta t_{0}$ is the time that passes for the stationary observer, $v$ is the relative velocity between the two observers. There is also ...

1

It's a matter of what you mean by "see". Even for a distant observer, it will take a small amount of time for the gravitational redshift effect to become essentially infinite. If your collapsing gas star redshifts to the point where it won't emit a single photon in the age of the universe, it may not have yet technically "redshifted to zero", but it has ...

1

My answer to your question is: no one can reliably answer your question. The model of the universe based solely on General Relativity says something about the beginning of the universe. If one follows the evolution of the universe backwards in time, one finds a singularity of infinite energy density "before" which the concept of time has no meaning. ...

1

The operation that seems to be causing you confusion is called a boost. A boost is an operation on minkowski space-time that in many ways is analagous to a rotation in three dimensional space. So let's make sure we understand the analogous situation dealing with rotations in three dimensional space. Rotations Let's imagine we have a stick which has a ...

1

Time is relative. When it comes to Time Dilation, you actually see dilated time of another observer. So, your own time flow won't get frozen in any case. Hypothetically, you can see another one's time frozen if she is traveling at speed of light (time dilation by speed) or she is at event horizon of Black Holes (gravitational time dilation). Unfortunately, ...

1

Is this true or false: If A and B have clocks and are traveling at relative velocity to each other, then to B it APPEARS that A's clock moving slower, but A sees his own clock moving at normal speed. Similarly, to A it APPEARS that B's clock is moving slower, but B sees his own clock moving at normal speed. This is true. If the above is true, then ...

Only top voted, non community-wiki answers of a minimum length are eligible