Universe Definition and 1000 Threads

I have read that the Schwarzschild radius of a black hole with the mass-energy of the observable universe is roughly equal to the actual Hubble radius of 13.8 billion light years. And I have read that contrary to some popular esoteric interpretations such as "the universe is a black hole", "we...

The conservation of the energy of the universe requires that the universe is an isolated system. Is there any way that, in fact, the universe isn't a isolated system and we would be losing or gaining energy in the universe? Also, does this possibly mean that the universe won't necessarily end in...

Imagine a universe where electrons and protons have positive and negative electric charges, respectively. Could an atom consisting of one electron and one proton exist in this universe?

Hi. I was recently researching the Hubble Sphere - a concept that is within cosmology - and someone claimed something interesting. The individual contended that the universe has been decelerating since the big bang, and that the so called "acceleration" in the expansion of the universe is space...

Homework Statement Assume the cosmological model with H0=72,Omega_M=1-Omega_lamda=0.3,(so dark energy with w = − 1) and a flat universe.) a) Find the redshift z at which the universe starts accelerating (that is, when it transitions from decelerating to accelerating). b) How long ago did this...

A 2-dimensional creature living on the surface of a 3-dimensional sphere could conclude he lives in a finite, unbounded universe. Is it necessary for a 3-dimensional creature to assume there is a 4th spatial dimension in order to conclude the universe is finite and unbounded? I have seen a...

When we view objects in the universe our eye sees the light that traveled from said object to our eye. When we see the Andromeda galaxy we are actually seeing the Andromeda galaxy as it was 2.5 million years ago. This raises a question about matter within the visible universe: Is there a...

In an article called "From big bang to big bounce" published in New Scientist in 2008, author Anil Ananthaswamy outlines two different theories that lead to our universe being cyclic. 1: "Cosmologists are still very much in the dark about dark energy. Some theoretical models speculate that the...

if we apply the laws of thermodynamics to the universe as the system, and factoring dynamic boundary and dynamic system, how could we define the surroundings as a non-infinite, non zero factor?

I would like to know what the community thinks about this game. Its a procedurally generated game set into a virtual Universe. As an Astronomy and Cosmology buff, I have a huge interest in this game and am quite excited about it's launch. I would be happy to see if the properties of the natural...

Could an infinite Universe ever end?

If I induce vacuum in a glass tube and then I open the lid of the glass tube, air rushes into fill in the vacuum. Can vacuum be regarded as a sort of potential energy, able to exert a force? Can a vacuum tube be considered as a potential storage device for energy, just like a container filled...

From this link https://en.wikipedia.org/wiki/Fine-tuned_Universe It seems that it is, what is the probability for such a universe?, has it gone through many iterations to come to be able to support life,? or was it a that life can be able to flourish or adapt to manifold of universes , for...

For example in DBZ, the level of power is determined by the ki, so what about the potter universe?

Why we don't feel the universe acceleration ? Thanks in advance

I know that quarks can never exist in isolation, and also group up so that they have a net neutral colour charge. But I am wondering at the start of the universe, or under very, very extreme conditions (such as the start of the universe) would quarks have been able to exist by themselves. I have...

I can't be the only person to ever have this thought so I am hoping one of you star gazers can tell me what I am missing. I understand Hubble's theory and the idea of space itself expanding. My question is this. If we know the universe is expanding because of the redshift and the farther away we...

Really good blog post by Sean Carroll on a shockingly common misconception: http://www.preposterousuniverse.com/blog/2015/10/13/the-universe-never-expands-faster-than-the-speed-of-light/ Hopefully at least scientists will stop spreading this misconception soon.

After learning a bit from the thread "The Dark Sky Ahead", I have tried to think through the dynamics of gravitational interactions in a simplified scenario. Unfortunately the GR math of the problem is over my head. My attempt below, using a simpler approach, leaves me quite confused. If my...

Hello I have question about universe density so is there any equation what says how to calculate universe density because on meany cosmology equations:wink:.

I know this question is quite odd as we're still researching on this, but is the universe speeding up, aka, accelerating? Or is the speed constant? Or is it slowing down? Thoughts? (PS - I don't know what the prefixes B I A means, I have chosen a random A, please consider if it's wrong, am...

As the universe expands, space itself gets "stretched" and objects drift apart, like dots on elastic surfaces when force is applied. So one meter billions of years ago is two meters today, but does it necessarily mean light takes twice as long to travel this "new meter"?

Homework Statement Assume that in an alternate universe, the laws of physics are very different from ours and that "ideal" gases behave as follows: (i) At constant temperature, pressure is inversely proportional to the square of the volume. (ii) At constant pressure, the volume varies directly...

I'm just beginning physics and teaching myself classical physics from an intro physics textbook and in the 2nd chapter it described reference frames. This got me thinking. My reference frame is the earth, as that is what I use to describe position, displacement, ect. But what is the reference...

my wife asked me after watching firefly, "how big is the actual universe?". I actually had no idea at the time and I was too lazy to get up and research it but I did have a calculator on my desk and a pad of paper so I wrote this. The actual size of the universe itself? I'm not sure of, but...

If we look up the sky at galaxy X whose light took Y amount of time to reach us from distance Z, where is the galaxy X now?

DaleSpam submitted a new PF Insights post PF's policy on Lorentz Ether Theory and Block Universe Continue reading the Original PF Insights Post.

What do we know or speculate as to the size of the visible and entire universe between the Planck time and the beginning of explosive inflation?

Would it always be identical? Would it ever be identical? Essentially with the current state of physics and taking quantum fluctuations into consideration, would it always be the same? Is there motion at T=0?Another question: If we restarted the Universe from the big bang and let it play out...

Celeste: A new model for cataloging the universe The roots of tradition run deep in astronomy. From Galileo and Copernicus to Hubble and Hawking, scientists and philosophers have been pondering the mysteries of the universe for centuries, scanning the sky with methods and models that, for the...

Hi, We all know the universe is expanding and it's doing so at a rate greater than the speed of light. But what does expansion mean? Popular Science videos usually give the loaf of bread example expanding in the oven. But even the loaf of bread has limits, it can only expand so far. Do we know...

How are we, and the universe effected from its accelerating expansion? Also how will our perception of the world around us be effected, since the universe is expanding and light is constant? <-Will things appear to move slower? I know that we only experience just a small fraction since the...

I read in "The Theory of Everything" of Stephen Hawking that all of the galaxies are running away from ours. That made me think that the Milky Way is the center of universe, since each galaxy is running away from us(like waves on the surface of water centered at one point which is the Milky...

Hello, I've a problem. I need to find the age of universe in normalized Planck units. In my case, I'm using Planck mass = 1 and: ##H = 1.18 × 10^{-61} \times t_P^{- 1}## With these values, how can I find the age of the universe? Thanks!

Hi PF members, I have a question about electromagnetic radiation propagating in an expanding universe. We know that because of space expansion, light from a distant source gets redshifted, its wavelength becoming longer and its amplitude flatter. If we move far enough from the source, we...

Why in ZC (ZFC-reemplacement+separation) can´t exist Von Neumann Universet not even till \omega2. Sorry, I am new in the forum and I dont´know use Latex

Is it possible to measure the universe' expansion in m/s^2 instead of metres per second per parsec?

According to Einsteinian Relativity, is the Universe considerably younger if one was to view it from within a greater distortion of the gravitational field? Is the value we assign for flat or non-flat universal age dependant on our own point of reference for time?

So, as I understand special relativity, when you go close to the speed of light, observers see you "shrink" in the direction of motion, and you see objects as shorter than they were when you were in the same frame, according to L=Lo√1-v2/c2. So suppose I am nearby Earth (in the same reference...

Hi All, I stumbled across these forums while googling for peoples thoughts on this question. I see that this similar question has be asked before some years ago, and I wanted to get current opinions and ideas on the following. I wonder about this and many of the mysteries we seem to...

If digital physics is true and physical reality consists of computations, then what could possibly be the computational platform, i.e. where could the computations be run on? What are possible answers explored in digital physics?

there are no electromagnetic waves? All I know is that there is a modified version of the Maxwell equations (in differential form) for such a universe, such as (the arrows represent vector arrows): →∇x →B = μ0 →j + μ0 ε0 ∂→B/∂t instead of having ∂E/dt in the last term (which would be the case...

Is it 'possible' (that is, if you say not, can you conclusively show the negative), that the entire observed acceleration in the expansion Our Universe, created some 13.7 x 10^9 years ago in the Big Bang, is due solely to centripetal force throughout, caused by a complex...

consider two concentric spheres, where inner radius is r and outer radius is r+delta. Assume space between the two spheres is mass of an amount to be solved for. Given the metric inside the sphere, assumed to be varying as implied by the Cosmic Background Radiation anisotropy (CBRa), can the...

This isn't too much of a question, but more of an open proposal. Now... to begin, I know that both you, reading this, and I can agree that our universe is expanding. The universe is expanding from every point within itself, there is no Defenitive reference point, this is a fact. So for an...

As opposed to antimatter, that is. The whole search for the asymmetry of matter vs antimatter seems to rest on the implicit assumption that what we observe is matter, not antimatter, no? Is there a way of distinguishing from afar between the two?

I'm new to this impressive forum and have a question that may have been addressed a thousand times, but here goes. A FLRW metric is happy with a time-varying scale factor a(t) and zero curvature parameter k and could care less about density. The combination of a FLRW metric and the Einstein...

[Moderator's note: Spun off from another thread, where it was off topic. Please start a new thread when you have questions on a new topic.] Photons lose energy when they travel long distances. Where does that energy go? What happens to that energy? Is there any theory regarding this?

Dear PF Forum, I have a simple and cliche question. What is the edge of the universe? 1. We live on the surface of the earth. It's 2 dimensions against Earth 3 dimensions. If we start from Equador which lies on the equator to the east, we'll reach Columbia then Brazil then Atlantic ocean...

if parallel universe are real... means according to schordinger equation..many possible states..then when we chose anyone state..then other options or i mean possible states would dissolve into one single option whom to chose... or remains present as a reality...?