Universe Definition and 1000 Threads

Summary: What is the size of the observable universe and a bit of a rant. I've only recently jumped down the rabbit hole of physics. A social media post on time dilation four months ago got me hooked. Not only has it been a great way to exercise my brain, some of its discovery has been...

Hello ! What do you think of this article ? https://www.nbcnews.com/mach/science/scientists-are-searching-mirror-universe-it-could-be-sitting-right-ncna1023206 The paper dates from 2017 : https://arxiv.org/abs/1710.00767 In my opinion, it is very speculative, but a mystery is not yet...

Summary: Looking for detail about what the recollapse of a closed universe would entail As I understand it, in a universe in which the density parameter is greater than 1, a closed universe, everything would eventually recollapse upon itself. My question is: does this recollapse just refer to...

I find this subject fascinating. Einstein said the distinctions between past, present and future is just a persistent illusion. I was watching a special with Brian Greene and other Physicist who think we do live in a Block Universe and they explained it very well. Here's my question. Say there...

As indicated in the title and summary, I'm wondering if there is any large scale astronomical effort to assess directly the universal spatial expansion assumed by the Doppler interpretation of the redshift/distance relationship, by measuring individual galaxy subtended angles over time. The...

Summary: How is the universe best viewed considering the great difference between smallest and largets things? I am not sure how to phrase this question so forgive me if it is all wrong. I have noticed that science is doing a lot with small, very small things. They also do a lot with big...

I came across this video today: Which summarizes this new paper from University of Tokyo: https://arxiv.org/pdf/1907.02273.pdf I get that the video is just an explainer for primordial black holes, but I was hoping to get a better explanation on exactly when conventional wisdom says density...

The age of the universe at the recombination is reported everywhere on the internet as 379,000 years. I would be grateful if someone could point me towards the paper where this is calculated.

So the universe is expanding, and galaxies are getting farther apart from one another on average. Does this motion count the same as ordinary motion, in that if a galaxy is being expanded away from us at 0.5c, that clocks in that galaxy would appear to tick slower at 0.866 the rate of clocks here?

Summary: How do we know that the universe is expanding? Am I correct in my understanding that we believe the universe is expanding due to the objects we can see, i.e. galaxy's moving away from us, and that the further away from us they are, the faster they apear to be receding away from us...

How would the first and second laws of thermodynamics apply to the creation and existence of the universe? I'm not a physicist (and unfortunately, do not remember a lot that I learned in Physics class in school and college about Thermodynamics). I did some searching and I have come across an...

Hello- I just watched (or tried to watch) a YouTube video by Fermilab, in which the speaker states that the universe has a definite "width" of 92 billion light years. I could only watch about half of it because more and more terms were used which it am not familiar with. Besides, his pedantic...

If the creation of our universe went alongside with creation of a second universe wherein each particle in our universe had a counterpart particle in it with opposite momentum, could those universes (our+second one) be created from zero energy?

The Hubble telescope was able to capture images of the edges of our visible universe in its deep space photos. These were among its most breathtaking pictures. They show galaxies from about 14 billion light years away, as well as in the past, from the very beginning of time and space in our...

The second law of thermodynamics tells us that the amount of useful energy in an isolated system tends to decrease. Does this imply that mankind will reach a point where it cannot longer use any kind of energy? If so, do we have an estimate of how long it will be necessary for to haven't useful...

What does quantum physics say about the simulation hypothesis?

Problem Statement Assumptions: a. The universe is finite. That is, it is (approximately) a 3D boundary of a 4D hyper-sphere of radius r. b. [The following is based on https://arxiv.org/pdf/1502.01589.pdf as discussed in the thread...

I snapped this picture with my VIVE. It's a red dwarf. Universe Sandbox is sooo cool.

Summary: Age of the universe Just a bit of a fun here, not sure how this equates into anything useful. So we believe the "age of the universe" to be around 13.8 billion years, it seems to me that this is a relative time frame based on the rate of flow of time on earth. I find myself wondering...

My questions are based on material from the following source. https://arxiv.org/pdf/1502.01589.pdf pg 26 Eqs 27 & 28 In the base CDM model, the Planck data constrain the Hubble constant H0 and matter density Ωm to high precision: H0=67.3±1.0 km s−1 Mpc−1 Ωm=0.315±0.013...

When discussing the shape of the universe (flatness/curvature), I often hear of three possible examples; spherical, flat and hyperbolic. Presenters will often use a 2-D analogy of how a flat sheet can be curved or shaped, like a saddle, table, or surface of a ball, where triangles can be defined...

What happens to the fabric of spacetime during the expansion of the universe? Does it stretch or expand? If it does not stretch or expand, does new spacetime form to "fill the gap" as such? Hypethotically speaking, I have two celestial objects separated by a gap 1 mile wide. Due to the...

I have not seen anything published siting a value, so being the curious type I was wondering if any has and what is the value? Also it would be nice to know at what Energy it is referenced to Thanks all, Bob

I realize that my understanding of this matter and it's vast number of related concepts is rudimentary and incomplete. Kindly forgive my ignorance and try to explain your thoughts in layman's terms. Thank you for your time.

Firstly i worked out the scale factor of the universe R(t)/R(t0) = 1/1+z = 1/1+11.1 = 1/12.1 = 12.1^3 = 1/1772 The distance between the galaxies were 12.1 times less than today and the volume was 1772 times smaller than today. Then I think the average density in the universe at that time is...

On Ned Wright's pages one can find this graph: plotting some supernova data against different expansion models. The main thing here that gives me a pause is the linear relationship for the closed universe with ##\Omega##=2 (red line). There doesn't seem to be any weird scaling involved. What is...

I was reading that the Big Rip will cause the whole universe to go singular, which sounds to me like another Big Bang. I was reading up on the Big Rip at Wikipedia, where it says that the observable universe is getting smaller, which makes no sense since the universe is expanding. :oldconfused:

Hi! Obviously my understanding is at a pretty elementary level, but nevertheless I'm puzzled by the reaction of astronomers and astrophysicists to the discrepancy in the measurements of the expansion of the early universe based on the Cosmic Microwave Background, and the measurements of its...

Thoughts on this finding? Does it really require new physics to explain? https://arxiv.org/pdf/1903.07603.pdf https://apnews.com/fac50d45a19f4239848b1712cfd22c36

We need to prove that a3(t)= ρo/2Λ [cosh(sqrt(24πGΛ)*t) -1] by changing into a variable of u, where u=2Λa3/ρo From Friedmann's second equation we know that Λ= ρm/ 2 Also ρm= ρo/ a3 [First attempt] I begin from Friedmann's equation where (for here), ρtotal= ρm + Λ and k=0; a'2/a2 = 8πG(ρm +...

I was reading this Quora post, and it seems to say that the late, great Stephen Hawking has proven this. https://www.quora.com/Have-scientists-disproved-Stephen-Hawkings-theories-of-the-universe

Now...exactly when and how do CMB photons lose their 3000˚ K creation energy to become 2.7˚ K?

If we took a snapshot of the entire universe (or if we stopped time) but still had the power to move around and measure, we could observe static properties such as: Mass Force Position From the above, we would be able to infer acceleration. But we couldn't observe present velocity and...

What if the universe suddenly started playing in reverse, like playing a recording in reverse. Particles gain kinetic energy from heat and sound energy as they travel the opposite way, light retreats back into the sun etc. Would this universe differ in any way? Does anything not work if time...

I don't think there is a thread on this? R Gusten et al, Nature, 2019, DOI: 10.1038/s41586-019-1090-x

I have been trying to think if there is no multiverse and the universe is not infinite than what is on the outside?

The other day I was playing my favorite time waster (World of Warcraft), and someone started to talk about flat earthers. I thought of stirring world chat a little bit, so I posted that while the flat earthers were a lot of odd folks, one could argue that for a photon the Earth indeed looks...

I saw another post about dS = dQ/T, but the subject of question was different - not related to the entropy of universe. This is what i understand from this formula: As the temperature goes down, the entropy goes up. Is this not the opposite (contradictory) to what entropy (disorder) is about...

The final result must be V=2π2α3 Hint says we must use the dV in the spherical system (dV=r2sin2θdrdθdφ) as well as the equation of the three-dimensional metric ds2= c2dt2 - a2[ dr2/(1-kr2) +r2(dθ2 +sin2θ dφ2) ] For a closed universe we know k=+1 and with dt=0 My problem is, I don't understand...

My understanding is that to define the entropy of a system what you have to do is as follows: Define the boundaries of your system. Define a set of "microstates" of the system. Define a partition of microstates of the system where each element of the partition is measurable and known as a...

The subject of the thread summarizes my question: Could the accelerating expansion be explained by a "spinning" universe?

Hermann Minkowski (Einsteins math instructor and a mathematical physicist himself): The views of space and time which I wish to lay before you have sprung from the soil of experimental physics, and therein lies their strength. They are radical. Henceforth space by itself, and time by itself...

If the galaxies we see are as they were a few million years ago, then how do we know that the universe is expanding since we don't know their current velocities? Hubble's graph shows a linearly proportional relationship between velocity and distance but the fact that the further a galaxy is, the...

How different would the universe look without dark matter? Would galaxies have formed, allowing for the existence of the solar system and life?

i have read that it is generally thought to be a consequence of the big bang (so, matter in motion) + something (dark energy) making that matter accelerate. why is the big bang needed in it? can't you just have acceleration? by the way, i am not sure what is intended by 'prefix' beside the...

Suppose we are in communication with aliens who live in a different universe. I know, that's impossible, communication requires the exchange of mass or energy, which implies that we live in the same universe. But suppose it is true. I am wondering, can we and the aliens, via this communication...

Sorry if this question is kind of vague or even too vague, but what is the universe's main descriptive action and what is the most common occurrence due to this action? Can we just say the universe's "main thing" is expansion and the main side effect of this process is...? -Side Question- Does...

Greg Bernhardt submitted a new blog post How to Create a Universe - Instructions for an Apprentice God Continue reading the Original Blog Post.

I am looking for the measurement data for distant objects (e.g. type Ia supernovae) The red shift and the luminosity flux data. What time interval is used in the luminosity flux measurement? What formula is used for the luminosity distance calculation?

As I am watching the current season of How the Universe Works, I am a bit confused when listening to physicists talking about energy as if it was a thing. The way I understand it, energy doesn't exist by itself, but is rather the result of interactions involving matter. Energy is released...