All Questions
352
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
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
92
votes
10
answers
20k
views
Why do scientists think that all the laws of physics that apply in our galaxy apply in other galaxies?
I like watching different videos about space. I keep seeing all these videos saying scientists found so and so at 200 billion light years away or this happened 13 billion years ago.
My question is ...
- 825
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
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
33
votes
9
answers
9k
views
Is space really expanding?
In a book called "Einstein, Relativity and Absolute Simultaneity" there was this sentence by Smith:
There is no observational evidence for a space expansion hypothesis. What is observed are ...
user311398
32
votes
7
answers
7k
views
Would there be no time in a universe with only light?
It is sometimes said, that if you stand still (in space), you travel through time at the speed of light. On the other side light never stands still, so it always only travels through space (at the ...
- 9,910
31
votes
1
answer
3k
views
Why haven't we seen the big bang?
The Andromeda galaxy is 2,538,000 light years away, so if we view Andromeda from a telescope, we see Andromeda how it was 2,538,000 years ago. Now the diameter of the visible universe is 92 billion ...
- 1,925
29
votes
5
answers
5k
views
What does the concept of an "infinite universe" actually mean?
When physicists talk about the universe being infinite, or wondering whether it is or not, what do these two options actually mean? I am not interested whether the universe is infinite or not, I am ...
- 406
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
25
votes
5
answers
5k
views
Does the universe have a fixed centre of mass?
Does the universe have a fixed centre of mass?
If it does, doesn't it necessarily mean that every action of ours has to be balanced by a counteraction somewhere in the universe so as to neutralize the ...
- 465
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
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
22
votes
5
answers
28k
views
Stephen Hawking says universe can create itself from nothing, but how exactly?
Stephen Hawking says in his latest book The Grand Design that,
Because there is a law such as gravity, the universe can and will create itself from nothing.
Is it not circular logic? I mean, how ...
- 329
20
votes
8
answers
13k
views
What is spacetime (simple explanation)? [duplicate]
Can someone please explain concept of spacetime in simple language? What is it and how it is important in the universe?
Wherever I have tried searching this concept, I have come across most ...
- 311