Expanding universe Definition and 230 Threads

My question is very simple but it is something I have been thinking about for some time. Every time a person needs to have the expansion of the Universe explained or the question "What does the Universe expand into?", people who know a bit about the topic answer that it expands into and onto...

As far as we know, the universe is undergoing accelerated expansion and heading towards empty de Sitter space. It is assumed that eventually the observable universe will be emptied out of matter and all radiation. Now if we take in account quantum mechanics, there's always non zero probability...

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 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...

Then is potential energy infinite (potential energy=energy that can be created)

As I understand it, the Universe is red-shifted (emission spectra) from any point of reference looking outwards. The Universe is expanding, but is matter being created at the same rate ? Does this mean that the density of matter in space is decreasing ? (density = mass / volume). What does this...

No matter what direction I point my super duper telescope, I will observe galaxies that are barely 500 million years old in every direction some of them being located 12+ billion light years away. So 2 galaxies on opposite side of the Earth should be twice 12+ billion light years apart. In other...

A rubber ball is bouncing on a flat surface. Every time it bounces, it loses energy, while the sound of the ball hitting the surface accelerates (because the intervals of the ball impacting the surface become shorter with each bounce). The ball seems to be accelerating when, in fact, it is...

We understand that for the Universe to be flat, the critical mass of everything that has mass must total an omega of 1.0. At first, with our lack of knowledge regarding dark energy, we thought that the universe that we detected (ordinary matter and dark matter) did not even add up to a third of...

OK I might be stupid and english isn't my native language, so I'm sorry in advance. So: The red shift is bigger, the further away a galaxy is (they move away faster), and the closer it is, the shift is smaller and it goes to blue for Andromeda (towards). Everyone knows that. BUT When you...

Good day. I do not know much about cosmology, rather computer science, but the following theoretical question bothers me a little. Some scientists, like Tegmark, Wolfram, Zuse or Fredkin, support the idea that the Universe might be just computation. Computable means that something can be...

If the Universe were not expanding uniformly (i.e., at the same rate in all places), then would different places would see a different Hubble law than we do? And if If the extragalactic distance scale changed, would the Hubble constant change?

These questions shows my lack of understanding of the expanding universe specifically the Friedmann equation. Here is a quote from Brian Greene (The Fabric of the Cosmos, page 273): “The early universe provided an arena in which gravity exerted its repulsive side with a vengeance, driving every...

Hello Everyone, Back when Einstein was formulating General Relativity his equations just could not predict a static universe. I have read that they actually predicted an expanding Universe. Later Friedmann derived an equation from GR that would explain how an Expanding Universe would evolve...

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...

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...

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...

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"?

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...

Is ther a term for the space that the expanding universe has not reached yet. Is it called a void or is it some other term. Also if you could link some articles about this space the universe hasnt reached yet I would love to read about it. Thank you all.

Hello, I've worked through most of Carroll's appendix on the non-coordinate basis. I see and agree how the spin connection and tetrad one-forms are useful while calculating. However as an example he sets out to apply the formalism to a spatially flat, expanding universe. ds^2 = -dt^2...

Hubble observed that not only is the universe expanding but that it is accelerating. With the model of the Big Bang as I understand it, the universe began as a big explosion. That would mean that it expanded at a rate exceeding the speed of light or at least close to it. If that is correct, that...

Viewpoint 1: Because gravity or other forces that are holding the thing concerned (be it a galaxy, a ruler or an atom) together are way stronger than the "force" caused by the expansion of space. So strictly speaking, space does in fact expand everywhere, including the space inside an atom...

I know that universe can be have three different futures.But for lastes theories universe is growing faster then we thought.I want to ask how much energy we need to make this observable universe.

The universe is expanding: Why is it that the further galaxies and stars are away from us they appear to be moving away at a much faster speed than ones closer to home?

Is the red shift evidence enough to define accelerated expansion

Is the expansion of the universe after the big bang just the the "uncurving" of space time from an inconceivable point? And if so, is the loss of energy that curved it that much the only thing that could allow it to "uncurve"? I hate to use the word loss of energy, but I'm not for sure where...

Why did dark energy overcome dark matter to create the expanding universe we live in today?

Please forgive my lack of knowledge about the more complex ways that we have determined that the rate at which the universe is expanding is increasing, but one thing puzzles me. I have read that based on measurements of the red shift of light we have concluded that the farther we look out into...

I'm trying to reconcile the fact that regions of the universe are expanding faster than light, and that as a consequence the observable universe is far more than 13.7 billion light years across. I trust these are the facts, but I'm stuck figuring out how we know these to be true. I feel like...

Could the accelerating rate of the expansion of the universe be due to the conversion of potential energy to kinetic energy? At the early stages of the big bang there would be tremendous amounts of potential energy (because it was so compressed). As it expanded, the universe, by the conservation...

As I understand it, space continues to expand everywhere. But bound systems such as atoms and solar systems stay the same size due to local interactions. If this be true, should not energy be continually released by this "falling in" of matter within every atom, molecule, and planetary system...

Hello anyone who can answer. I have a question concerning dark energy (Please realize that my knowledge is limited on this subject) It is known that the universe is expanding at an accelerating rate, scientists say this is due to the mysterious dark energy. It seems to go against our...

How one can say that the space is expanding by just verifying that the galaxies are speeding away from each other?

I had some interesting ideas concerning the mechanics behind the space expansion and its acceleration. Here they are. I know you expect blunders, but I hope you will find something interesting. Starting with obvious:1. In the presence of strong gravitational field, time flows slower than in its...

We all know the concept of the universe expanding. Would it be possible that the universe is not expanding at all, but the spacetime between objects is increasing? My question comes from the idea that spacetime is changed due to the presence of gravitational objects and the idea that gravity is...

Rephrase from another thread I posted a while back; If you believe as masses increase in distance gravitational potential increases relative to the distance (the greater the distance the greater the gravitational potential). So as matter increases in distance from each other due to...

I've always been curious about about the big bang because (from what I've read) it's a point we're not able predict before. Is there a possibility that our view of an expanding universe just means we can't see beyond the big bang? Or is there a reason that is ruled out and that everything...

The energy 'U' of a uniform spherical volume (e.g., a Hubble sphere) is (3/5)(M^2)G/R Conventional wisdom has it that G and M are constant - at least in the preferred models that we are permitted to discuss on these forums. So when the Hubble sphere expands, we really don't expect a loss of...

Universe is expanding. I know that all the galaxies are getting away from each other due to the expansion. So in theory is it true that we along with every other system of particles are getting stretched with the space ( or the distance between our constituent particle is getting bigger and...

I would like to ask something. How is the solution of EOM for the action (for FRW metric): S= \int d^{4}x \sqrt{-g} [ (\partial _{\mu} \phi)^{2} - V(\phi) ] give solution of: \ddot{\phi} + 3H \dot{\phi} + V'(\phi) =0 I don't in fact understand how the 2nd term appears... it...

Universe is expanding which means the Earth is getting away from the sun. Without the sun, it is probably that all organisms on the Earth would die. Is there any calculation or estimation from scientists that how many years before the Earth is too far away from the sun so that we will all die

Finding a constant in an axpanding univarse Hi, I want to obtain a constant that proportional to total matter density of universe. Let ρ be matter densitiy and ρr be radiation desity. In an expanding universe volume times total density must be constant. It is wrong? let me show it...

A homogeneous and isotropic Universe is described by the FLRW metric: ds^2 = c^2dt^2 + a^2(t)\ d\Sigma^2, where ##a(t)## is the scale factor and ##d\Sigma## is an interval of uniformly curved co-ordinate 3-space which is independent of cosmic time ##t##. If we set ##dt=0## then we find that...

I have trouble understanding the following. Lets take 2 galaxies moving away from each other caused by the expanding universe. A spaceship traveling between these 2 galaxies, more than one time, will experience a greater distance for each travel. Therefore my conclusion is, that there must...

For simplicity I assume a flat radial FRW metric (with c=1): ds^2 = -dt^2 + a^2(t)\ dr^2 Now let us consider the path of a light ray, a null geodesic, with ds=0 so that we have: dt = a(t)\ dr Now at the present time t_0 we define a(t_0)=1 so that we have: dt_0 = dr The interval of radial...

Since the speed of light is a constant, no matter what location from which a search of the universe is made, matter would appear to be accelerating in the expansion in the same way to the observer. It is understood that about 14 billion years ago the expansion started. From any vantage point...

Space is expanding equally from all points Galaxies are moving away from each other contrary to gravity. However gravity overcomes expansion between nearby galaxies and within the galaxy and the nuclear forces overcome the expansion within matter. What is the formula to determine what the...

The figures in http://www.astro.virginia.edu/class/whittle/astr553/Topic16/t16_light_cones.html are very useful in understanding the various world lines in concordant diagrams. Is there any easy way to see how a velocity cone (at the observer's worldline) from a later time than the Big Bang...

If we are looking further and further back in time when we look at more and more distant galaxies, then how do we know that they are accelerating (instead of that they were accelerating a long long time ago)??