Linked Questions

-3
votes
1answer
166 views

Must the origin of the universe be non-physical? [duplicate]

Since the 2nd law of thermodynamics says the universe's entropy is constantly increasing, then its initial entropy must have been smaller than it is today. However, no known physical law can reduce ...
3
votes
1answer
91 views

How could the early Universe have low entropy when it was so compact? [duplicate]

Entropy of a system can be understood as "the number of states that are macroscopically indistinguishable from the state its currently in". (Sean Carroll, "The Big Picture") Given that the early ...
32
votes
10answers
7k views

How can it be that the beginning universe had a high temperature and a low entropy at the same time?

The Big Bang theory assumes that our universe started from a very/infinitely dense and extremely/infinitely hot state. But on the other side, it is often claimed that our universe must have been ...
3
votes
4answers
3k views

How is the entropy at the time of the Big Bang calculated?

I've seen several reports that the entropy of the Universe at the time of the Big Bang was lower than it is now. This seems impossible. If we view entropy as a function of the number of micro ...
14
votes
5answers
565 views

Was there a first moment in time?

Disclaimer. I am a mathematician, not a physicist. The extent of my physics training is a couple of high school courses. So, you may have to be very patient with me in understanding your answer(s)/...
14
votes
3answers
5k views

Why does the low entropy at the big bang require an explanation? (cosmological arrow of time)

I have read Sean Carrol's book. I have listened to Roger Penrose talk on "Before the Big Bang". Both are offering to explain the mystery of low entropy, highly ordered state, at the Big Bang. Since ...
1
vote
3answers
2k views

What does it mean that the laws of physics are time reversible?

The Universe, as far as we can tell, only operates according to laws of physics. And just about all of the laws of physics that we know are completely time-reversible, meaning that the things they ...
9
votes
3answers
603 views

Did really everything begin with a state with very low entropy?

As emphasized by Penrose many years ago, cosmology can only make sense if the world started in a state of exceptionally low entropy. The low entropy starting point is the ultimate reason that the ...
1
vote
1answer
479 views

Do laws of thermodynamics have a place in Theory of Everything? [closed]

I am having a difficulty understanding why second law of thermodynamics is still a valid universally accepted concept. I understand it works on paper for describing isolated heat systems. However, I ...
0
votes
2answers
395 views

Simplifying the explanation of a low-entropy Big Bang

The claim that the young universe was in a low-entropy state seems at odds with maximal entropy being thermal equilibrium, and the young universe being in thermal equilibrium. I've looked at some ...
0
votes
0answers
81 views

Understanding time [duplicate]

Am sorry if this is a silly question. I have heard something like this from cosmologists: "There is no intrinsic arrow of time. Today, we believe that the direction of this arrow is due to our ...
1
vote
0answers
60 views

Did the early universe violate the 2nd law of thermodynamics? [duplicate]

If the universe started out isotropic and homogenous and of all fundamental particles then how could there now be any concentration of energy anywhere? If you say that nothing is really homogenous ...
0
votes
0answers
21 views

Could wave packet spreading of the universe explain the low entropy of the early universe?

Entropy of position and wave packet spreading. Why do wave packets spread out over time? Wave packet of the universe and its  spreading. Why was the universe in such an extraordinarily low entropy ...