The universe tag has no wiki summary.
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6answers
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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 ...
-7
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7answers
2k views
Does Quantum Physics really suggests this universe as a computer simulation? [closed]
I was reading about interesting article here which suggests that our universe is a big computer simulation and the proof of it is a Quantum Physics.
I know quantum physics tries to provide some ...
7
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2answers
1k views
Is reality discrete at the quantum level? (…and what does it imply not only mathematically?)
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 ...
8
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3answers
1k views
What has been proved about the big bang, and what has not?
Ok so the universe is in constant expansion, that has been proven, right? And that means that it was smaller in the past.. But what's the smallest size we can be sure the universe has ever had?
I ...
3
votes
4answers
354 views
Origins of the universe questions
If the universe is expanding, what is it expanding into?
Similarly when the big bang happened where and how did it occur? - Where did the energy come from? Energy can not be created or destroyed does ...
6
votes
4answers
913 views
Shape of the universe?
What is the exact shape of the universe? I know of the balloon analogy, and the bread with raisins in it. These clarify some points, like how the universe can have no centre, and how it can expand ...
4
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3answers
232 views
Can we prove that the universe is finite or infinite?
If I say that the universe is finite, how can you say with certain that I am wrong?
5
votes
3answers
422 views
How can a quasar be 29 billion light-years away from Earth if Big Bang happened only 13.8 billion years ago?
I was reading through the Wikipedia article on Quasars and came across the fact that the most distant Quasar is 29 Billion Light years. This is what the article exactly says
The highest redshift ...
6
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4answers
1k views
Did time exist before the creation of matter in the universe?
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 ...
8
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2answers
393 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 ...
6
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3answers
520 views
At what speed does our universe expand?
Conceivably it expands with the speed of light. I do not know, but curious, if there is an answer. At what velocity, does our universe expand?
4
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5answers
5k 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
vote
1answer
228 views
Superluminal expansion of the early universe how is this possible?
Is this a postulate? I get the expansion of the universe, the addition of discrete bits of space time between me and a distant galaxy, until very distant parts of the universe are moving relative to ...
4
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5answers
3k views
How can something happen when time does not exist?
I saw this documentary hosted by Stephen Hawkins: www.youtube.com/watch?v=WQhd05ZVYWg
And if I didn't get it wrong, it says that there was no time before the big bang, time was created there.
So how ...
9
votes
6answers
982 views
Does anything exist in the intergalactic space?
I am a part time physics enthusiast and I seldom wonder about the intergalactic space. First, it is my perception that all(almost all) the objects in the universe are organized in the forms of ...
4
votes
4answers
552 views
Experimental evidence for parallel universes
My idea of physics is that it is a collection of mathematical laws relating observables. And that one can perform alot of mathematical derivations on these laws to produce new laws between ...
9
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3answers
52 views
Seeing cosmic activity now, really means it happens millions/billions of years ago?
A Recent report about a cosmic burst 3.8 billion light years away. It is written as though it is happening now. However, my question is, if the event is 3.8 billion light years away, doesn't that mean ...
32
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8answers
2k views
Is time continuous?
I was making universe simulations, and I noticed that I implemented discrete time (the only type possible on computers). By that, I mean that I had an update function, that was called many times per ...
4
votes
1answer
556 views
Supermassive black holes with the density of the Universe
This question was inspired by the answer to the question "If the universe were compressed into a super massive black hole, how big would it be"
Assume that we have a matter with a uniform density ...
5
votes
1answer
964 views
How can something finite become infinite?
How can the universe become infinite in spatial extent if it started as a singularity, wouldn't it take infinite time to expand into an infinite universe?
0
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1answer
261 views
Are We Living in a Simulated Universe? [closed]
If the universe is just a Matrix- like simulation, how could we ever know? Physicist Silas Beane of the University of Bonn, Germany, thinks he has the answer!. His paper “Constraints on the Universe ...
12
votes
3answers
104 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 ...
6
votes
6answers
845 views
What are the most realistic ways of high speed space propulsion?
Liquid and solid chemical fuels in rockets are very expensive and inefficient. I have heard of solar sails but what are the most realistic space travel fuels that will be used in the future to get ...
4
votes
5answers
495 views
What is the extent of the universe?
Is there any realistic, understandable, provable (even in some extent) explanation/model for the extent of the universe?
What is its shape? and Why? I mean physical explanations not philosophical ...
16
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3answers
2k views
Why is the universe so big?
The Universe is approximately 13.7 billion years old. But yet it is 80 billion light years across. Isn't this a contradiction?
7
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4answers
489 views
How is it possible for astronomers to see something 13B light years away?
In a NPR News story from a few years back:
"A gamma-ray burst from about 13
billion light years away has become
the most distant object in the known
universe."
I'm a layman when it comes ...
5
votes
2answers
102 views
Is there a consensus on the fate of our universe?
We all know that our universe is inflating from what is known as the Big Bang. However, will our universe continue to inflate at the current rate? Or after reaching a maximum size, will it collapse in ...
4
votes
2answers
80 views
How is the shape of the universe measured by scientists?
I would like to learn how scientists go about measuring the large-scale curvature of the universe to determine if the universe is closed 'i.e. spherical', flat, or open 'i.e. saddle shaped'.
My ...
9
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7answers
1k views
How many bits are needed to simulate the universe?
This is not the same as: How many bytes can the observable universe store?
The Bekenstein bound tells us how many bits of data can be stored in a space. Using this value, we can determine the ...
11
votes
5answers
735 views
How many times has the “stuff” in our solar system been recycled from previous stars?
Is there a cosmologist in the house? I've got a basic understanding (with some degree of error) of some simple facts:
The Universe is a little over 13 billion years old. Our galaxy is almost that ...
4
votes
4answers
848 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 ...
4
votes
3answers
343 views
Why did decoherence start in the first place?
We learn that the quantum wave function $\Psi$ collapses when it interacts with a classic object (measurement).
My question is: Why are there classic objects after all, how did it all start? In a ...
1
vote
1answer
683 views
Zero energy universe
Regarding this thread:
http://www.physicsforums.com/showthread.php?t=506985
Why is the idea that the total energy in the universe "zero" so popular (re: Laurence Krauss) and why is the flatness of ...
6
votes
4answers
484 views
Is space unending?
Is the space unending, i.e it has no boundaries? If yes, how can a thing exist which is non-ending? Its impossible for me to imagine something like that. Secondly, if its not and has boundaries then ...
6
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1answer
448 views
Alternative theories to the big bang?
Hey all, are there any theories out there on the origins (or infinite existence of) the universe beside the big bang that actually adhere to current scientific knowledge and fact?
5
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4answers
1k views
Infinite universe - Jumping to pointless conclusions
I watched an episode of thee BBC Horizon series titled 'To infinity and beyond'.
In this program a number of respected physicists and mathematicians were talking about the nature of infinity and an ...
4
votes
3answers
192 views
Is the cosmic horizon related to the Big Bang event?
The Universe expands according to the Hubble's law: velocity is proportional to distance.
There must be some distance, therefore, at which the velocity reaches the speed of light. This defines the ...
3
votes
3answers
602 views
Is there a finite amount of mass in the universe?
So, I'm not too physics savvy but I am curious to ask. Is there a finite amount of mass in the universe? or is there more and more being created from somewhere or something? If the universe is ...
3
votes
2answers
407 views
Do we live in a world with 4 or more dimension?
A NOVA show have told the audience that we are live in 3 dimensional world, the world we lived in is compose by 3 element: the energy, matter, space. By the time Einstein have invented the ...
2
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1answer
107 views
acceleration of the universe
Moments after the Big Bang, the universe was expanding at an incredible rate, (I've heard) faster than the speed of light. Due to dark energy, scientists predict the rate of expansion will pick up ...
1
vote
1answer
338 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 ...
6
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3answers
444 views
Is the total energy of the universe constant?
If total energy is conserved just transformed and never newly created, is there a sum of all energies that is constant? Why is it probably not that easy?
4
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2answers
157 views
Total Energy of the Universe?
I've heard the total energy is zero, but I've also heard it cannot be said to be zero since there's so much unknown stuff in the universe. Is that true?
3
votes
2answers
100 views
How/why can the cosmic background radiation measurements tell us anything about the curvature of the universe?
So I've read the Wikipedia articles on WMAP and CMB in an attempt to try to understand how scientists are able to deduce the curvature of the universe from the measurements of the CMB.
The Wiki ...
3
votes
1answer
368 views
Is the universe finite and discrete?
Is the universe finite, both in the sense of being a closed spacetime manifold, as viewed from the macro level, but also in the sense of being fully discrete and finite in all of its intricate quantum ...
2
votes
1answer
842 views
Hubble time, the age of the Universe and expansion rate
The Hubble time is about 14 billion years. The estimated current age of the Universe is about 13.7 billion years. Is the reason these two time are so close (a) a coincidence, or (b) a reflection that ...
2
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1answer
247 views
What happend with the light from all the galaxies visibles from an earth telescope?
Supposing it's possible to see some distant galaxies with an earth telescope, then, at the tip of the telescope lens there are photons comming from the distant galaxy...
So, if I extend my hand in a ...
1
vote
1answer
47 views
Would the universe get consumed by blackholes because of entropy?
Since the total entropy of the universe is increasing because of spontaneous processes, black holes form because of entropy (correct me if I'm wrong), and the universe is always expanding, would the ...
1
vote
0answers
43 views
Is the speed of light the ultimate speed limit? [duplicate]
As we all know nothing can go faster than the speed of light as mentioned by most of our pioneer's in physics. But as I was listening to one of the statements of Sir. Stephen Hawkins he stated that at ...
1
vote
1answer
415 views
is gravity always the weakest force [duplicate]
Possible Duplicate:
What does it mean to say “Gravity is the weakest of the forces”?
Strongest force in nature
It is usually taught that the gravitational force is the weakest ...
