Universe Definition and 1000 Threads

Our general understanding of the universe is that it is infinite, so how can it be growing? If the universe is everything then what is it growing into?

Is our known universe expanding? Hypothetically we should we be seeing a light year further every year as the light hits us from distant stars. However once we take into account the expansion of the universe, are we really seeing any further? I am confused by the while topic of light and being...

Hypothetically, what does the edge of the universe look like? Past our known visible universe to the edge of the expanding universe what is it like?

We see it frequently stated that in the subatomic/quantum world, there is no reason that the arrow of time points in only one direction, that either direction for particles is equally valid and workable. (If I am mis-stating this let me know.) But what is the model of the universe that is...

If the big bang through matter in every direction away from itself (the center) shouldn't there be a huge void there?

Is a classical universe (with a deterministic dynamics) compatible with assuming that experimental choices can be made arbitrarily? This question arises from the following statement of Bell: that I had cited (with a reference) in https://www.physicsforums.com/posts/5694545/, and commented...

That was 10 years ago, when he proposed that humans are shortening the lifespan of the universe by looking at it. Is this nonsense?

Ok..I know that at some point, from the Hubble Law , galaxies will seem to moving away from us speed of light,But actaully they can't because the space-time itself expands so it will be like a black hole horizon,which within that radius its , c/H , we can observe things etc.But out of that...

Hello guys, I was reading some models about the topology and size of the universe (always a controversial topic), then a question came to my mind. It is predicted that our universe will expand until it reaches heat death. Can a closed, finite universe also reach heat death and be described by...

Hi everyone, I was thinking of a new theory in physics regarding dark energy, black holes and the accelerating expanding universe. What if most of the matter created by the Big Bang was pushed at the edge of the new created space/time like explosions, the matter is at the edge of the explosion...

Hello. This is my first post here. I have a question about the age of the universe that has been on my mind for the last few weeks. I have just read the posting guidelines and wish to state before I begin that I do not intend this as a challenge to mainstream theory but as an attempt to...

I'm sure this is probably a stupid question with an obvious answer.. But i can't come up with it.. So, the observable universe is ment to be 90 billion lightyears across, right? And it's 13.8 billion years old, right? And a lightyear is the distance it takes for light and fields and stuff to...

I am trying to find an animation (from the internet) explaining the intricate balance of heavenly bodies (stars, planets, satellites, comets etc) in their own orbits. What happens if there is a sudden change in anyone of characteristics of those heavenly bodies. Is a small perturbation in...

My understanding of physics and mathematics and what nots is self taught and frankly really rather amateur compared to the people who use this forum, but one thing that really fascinates me is the holographic universe theory. Would you be able to explain the pros and cons of the arguments and...

Friedmann's Eq can be viewed here https://ned.ipac.caltech.edu/level5/March08/Frieman/Equations/paper1x.gif What I don't get is that all the texts/analyses of Friedmann's equation say that if the right hand side is negative it means that the universe will expand reach a critical point and then...

I have just found this paper that states the universe is expanding faster the further we look back, Different than the Hubble measured.? https://www.sciencedaily.com/releases/2017/01/170126132624.htm The new measurement is completely independent of -- but in excellent agreement with -- other...

I know that in observable universe energy is not conserved.I don't know exactly why (it s possibly about GR and expanding universe but I don't know the equations) In the observable universe...If we take a whole system like entire Observable universe, In this system is momentum conserved ...

I am not a proponent of holographic principle, I believe the universe is infinite, one will start off and not come back to the same starting point , my question is how popular is the holographic principle? and why? Not that my views mean any thing...

I can not find a paper on this, but is it possible that the universe is expanding faster than expected? https://www.sciencedaily.com/releases/2017/01/170126132624.htm Because galaxies do not create perfectly spherical distortions in the fabric of space and the lensing galaxies and quasars are...

If the universe is past eternal, then why has it not reach heat death by now? If given infinite past time it should have already arrived at such a state and should exist in thermodynamic equilibrium. Some argue that the 2nd Law of Thermo rules out any possibility of a past eternal universe.

Hi guys, Based on what I know about the status of modern cosmology the question whether the universe is infinite or finite in extent is still open. Are there any plausible models in which the universe is finite and closed, despite the curvature being close to flat? Thanks in advance.

Hi all, I would like some thoughts on the following quote I read from a book on the history of QM: "Quantum: Einstein, Bohr, And the Great Debate About the Nature of Reality." Please restrict your consideration to the Bohr/Heisenberg 'Copenhagen' interpretation (I realize in other...

"Before the big bang, scientists believe, the entire vastness of the observable universe, including all of its matter and radiation, was compressed into a hot, dense mass just a few millimeters across." Isn't this describing what the singularity of a black hole is? Black holes spin extremely...

Hello I have been reading Sean Carroll's book "From eternity to here" where he mentioned the concept of functioning brains emerging from random fluctuations on a quantum level due to the expansion of universe. They have been called Boltzmann brains https://en.wikipedia.org/wiki/Boltzmann_brain...

Let's imagine a deterministic universe. A one where quantum mechanics simply doesn't apply. Ok. This was the universe of classical physics. Atoms exist, and they behave deterministically. Fine. Now, how can entropy increase in this universe, altough it has the same laws of physics. In a...

Thinking about 'everything' out there and the more and more convoluted way we have to arrange our maths and physics to explain the universe. I am starting to wonder if it's our brain is at fault. The human brain can only think in 3 dimensions maybe 4 with time, but that is one-directional...

Hello, When we assume the universe is expanding at a constant rate, we could say the age of the universe is 1/Ho. but I always feel unsure about that because 1/Ho is the distance over the velocity. However, the velocity changes over time, that is, when something is closer to us, the move slower...

Is there a minimal amount of information that one could use to make a universe, is this what string theory tries to do, I mean how much information would one need to make all the elementary particles, and how would one input energy to them, and what rules would be needed to build this universe...

I am not sure about how micro and macro spaces communicate information, but this paper seems to need it for gravity to emerge. The paper is far to advanced for me to understand completely https://arxiv.org/pdf/1611.02269v2.pdf It also seems that in this paper that gravity and space time...

If the universe is infinitely large, has it always been so? If space and time did not exist outside the big bang, was the universe at the time of the big bang infinitely large? Does this suggest the vacuum of space was infinitely large and the big bang is expanding within it?

At the big bang, 'we' (an inside observer) were traveling at great speeds. Does this mean to say that time was 'slower' and thus the value (distance traveled in time) of time within 1 second, experienced by an inside observer, was much larger than our modern, perceived, value of 1 second? If so...

The reason why I have this question is because I’ve been thinking that the observable universe is filled with galaxies and planets mostly around stars , and we also have explored that there are a lot of black holes in the universe which if I’m correct are simply dead stars which once had energy...

Are there any plausible models based on current evidence about the universe which ends in some way and doesn't last forever? I am aware that the accelerated expansion leads to eventual heat death for eternity, but are there any other plausible ideas what can happen?

Hey ! i am having this question to be answered , i am new to the cosmology studies and still a bit confused about some formulas. the question is: (a) The greatest redshift known corresponds to the cosmic microwave background (CMB, CBR) at redshift z 1100 (although the redshift is obtained...

Conservation of energy Is the law of conservation of energy absolute? If so, doesn't it follow that all the energy of the big bang came from somewhere? That the energy of our universe must predate the big bang? Isn't that circumstantial evidence of the validity of string theory which...

This may be a very trivial question. I would like to know how a universe could be flat if we are 3 dimensional. When i think of "flat" i think of something similar to a sheet of paper. Although technically 3 dimensional, the paper looks pretty 2 dimensional. So how is 3 dimensional space time...

Hello Everyone, This is my first post, and I don't have any formal background in cosmology. I'm in the middle of reading a book called 'The Exploration of Outer Space' by Sir Bernard Lovell and I find myself falling in love with this topic! I have a question that has gnawed at my head for a...

Did the universe Absolutely begin?

If the universe is indeed flat and the cosmological principle holds true, does this mean that there is an infinite amount of space in the universe as well as an infinite amount of matter?

We know from observations that the universe is expanding and that the speed of recession of celestial objects increases the further we look back in space. However, looking further in space is also looking back in time, so does this mean that we are looking at the end of inflation ?

What actually means to say that the universe is spatially flat? Would it be that, if one could extend two straight rods of infinite length (assuming a universe with no boundaries and infinite amount of material for making the rods, LOL), they would remain parallel?

They say that the universe started with low entropy, which is a certain amount of information. But I wonder how the information associated with the whole universe can change. By definition nothing can ever leaves or enters the universe as a whole. And if nothing ever enters or leaves a system...

Dear All I have a project related to the early universe and general relativity. Can anyone suggest me a book to start with? Thank you

Hello, for those who don't know me I'm layman with some knowledge at popular science level. Discussing with a friend we came to the following point and I would like to ask it here because we had doubts about our reasoning. Cramer's Transactional Interpretation proposes that, in a sense, a...

Hey guys, According to most pop science sources, "before" the Universe started to exist, there were no time, which can be understand easily as time is only possible if there are at least two existing object (e.g. two quarks, two atoms, etc.). Time as I understand it is a measurement of...

As the universe expands and is per definition gravitationally decoupled on long distances and the overall metric therefore is "flat" and apparently no gravitational background exists, the question in some discussion arose: Can GWs propagate in in a gravitational empty space at all? If not, and...

...(after infinite distance) falls into earth, would exist infinite potential energy if E=mgh and h is infinite?

If the visible universe began as a single dot and inflated in a very short time then its size as measured from standard candles and red shifts would presumably give us its present size and speed of regression. But its age wouldn't be the same number of years as the number of light years of its...

Homework Statement Currently, the density of matter ##\rho_0^M## and of radiation ##\rho_0^R## have values of approximately ##10^{-29}## g/cm^3 and ##10^{-33}## g/cm^3 respectively. Estimate the ratio of the cosmic scale factors ##a_{eq}## (scale factor at equality) and ##a_0## (scale factor...

I just read about how professor Erik Verlinde saying that 'gravity is not a fundamental force of nature, but an emergent phenomenon. In the same way that temperature arises from the movement of microscopic particles, gravity emerges from the changes of fundamental bits of information, stored in...