All Questions
76
questions
149
votes
2
answers
29k
views
Does the Planck scale imply that spacetime is discrete?
On a quantum scale the smallest unit is the Planck scale, which is a discrete measure.
There several question that come to mind:
Does that mean that particles can only live in a discrete grid-like ...
- 3,711
60
votes
4
answers
8k
views
Does the universe have a center? [duplicate]
If the big bang was the birth of everything, and the big bang was an event in the sense that it had a location and a time (time 0), wouldn't that mean that our universe has a center?
Where was the ...
- 1,269
74
votes
7
answers
32k
views
Is spacetime discrete or continuous?
Is the spacetime continuous or discrete?
Or better, is the 4-dimensional spacetime of general-relativity discrete or continuous? What if we consider additional dimensions like string theory ...
- 1,277
29
votes
7
answers
29k
views
Is the universe finite or infinite?
I thought the universe was finite, but then I read this:
How can something finite become infinite?
And they seem to assume it is infinite. So which is it?
- 1,387
125
votes
6
answers
11k
views
What is known about the topological structure of spacetime?
General relativity says that spacetime is a Lorentzian 4-manifold $M$ whose metric satisfies Einstein's field equations. I have two questions:
What topological restrictions do Einstein's equations ...
- 1,734
18
votes
6
answers
17k
views
Did time exist before the Big Bang and the creation of the universe? [duplicate]
Does time stretch all the way back for infinity or was there a point when time appears to start in the universe?
I remember reading long ago somewhere that according to one theory time began shortly ...
- 384
7
votes
5
answers
1k
views
What if the size of the Universe doubled?
My question has a silly formulation, but I want to know if there is some sensible physical question buried in it:
Suppose an exact copy of our Universe is made, but where spatial distances and sizes ...
- 5,220
23
votes
5
answers
8k
views
Hubble's law and conservation of energy
If all distances are constantly increasing, as Hubble's law say, then lots of potential energies of form ~$\frac{1}{r}$ changes, so how is the total energy of the Universe conserved with Hubble's ...
- 5,220
7
votes
1
answer
903
views
Doesn't dating the universe violate the concept of spacetime's inseparability?
It would seem that measuring an age of the universe from the big bang requires separating spacetime into a 3D coordinate system and a time track. I fail to understand why it is appropriate to take ...
- 121
15
votes
6
answers
17k
views
What is our location relative to the Big Bang?
Given what we know about space, time and the movement of galaxies, have we or can we determine what our position is in relation to the projected location of the Big Bang? I've read some introductory ...
- 261
3
votes
1
answer
2k
views
Universe Expansion as an absolute time reference
Why we call "constant" to the Hubble constant?,
if the universe were really expanding then the Hubble "constant" should change, being variable, smaller and smaller..with "time".
Other example/view ...
- 2,909
22
votes
3
answers
9k
views
What is meant when it is said that the universe is homogeneous and isotropic?
It is sometimes said that the universe is homogeneous and isotropic. What is meant by each of these descriptions? Are they mutually exclusive, or does one require the other? And what implications rise ...
- 3,439
11
votes
5
answers
2k
views
Does (it make sense to say that ) the universe has a center?
I was reading this page:
http://www.guardian.co.uk/science/2011/oct/23/brian-cox-jeff-forshaw-answers
and I found this sentence by Brian Cox:
That seems to imply that everything is flying away ...
- 221
2
votes
3
answers
2k
views
Whats left at the center of the Universe after Big bang?
If you consider big bang. According to that What's left at the center of universe where the Big bang occured?
- 75
20
votes
2
answers
3k
views
Is spacetime simply connected?
As I've stated in a prior question of mine, I am a mathematician with very little knowledge of Physics, and I ask here things I'm curious about/things that will help me learn.
This falls into the ...
- 847