Expansion of the universe Definition and 25 Threads

What is the maximal comoving distance that a probe can reach depending on its speed? If the probe travels at light speed, the maximal comoving distance that it can reach is 5 Mpc, which is called the cosmic event horizon. But what if it travels at some other speed?

I was reading these papers by Sean Carroll (https://arxiv.org/abs/1405.0298; https://arxiv.org/abs/1505.02780) in which, among other things, he argues against vacuum up-tunneling occurring in the universe. He only acknowledged that it would be possible in the first moments of the universe while...

I've found this discussion (https://astronomy.stackexchange.com/questions/43525/is-there-an-equivalent-of-the-red-shift-effect-for-cosmic-rays) where it is said that there is an equivalent redshift of cosmic rays due to the cosmic expansion However, how can this be? Cosmic rays are not EM...

This is my first (non-professional) post: It seems accepted that space is "created" (otherwise the expansion of the universe would exceed the speed of light). We are talking about "creation" (!!). The question would be: does current physics tell us if this represents a waste of energy for the...

I had a question about this paper (https://arxiv.org/abs/1401.3742) There, the authors indicate that dark energy competes against gravity in oversdensities and can slow down or even prevent their collapse. I have a simple question about this: Galaxies will in principle evaporate their outer...

Hello I have a question about space. I am no physicist nor student of any kind of science but I'm curious and I've heard some things about the speeding up of the expansion of the universe which got me thinking... If the expansion is accelerating without end and believed to even surpass the...

Spacetime expands at an accelerated rate and the particles with movement associated to this expansion are coupled to the Hubble flow. In many papers that I've read, objects coupled to the Hubble flow are treated as if they have some velocity and kinetic energy associated with it.However, can...

I found a paper (https://arxiv.org/pdf/astro-ph/0411299.pdf) which talks about quantum systems emitting energy due to spacetime expansion. Is this true or only a hypothesis?

There is an article written by astrophysicist Edward Harrison [1] which defends that energy could be extracted from attaching an imaginary cosmologically long string to a receding object from us in an expanding universe. He says that the energy extracted is potentially limited (in decelerating...

I was reading an article by Edward Harrison, which tackles the problems of conservation of energy at cosmological scales. At some point (point 2.4) he cites several article, including one by Rees and Gott, which he says indicates that the internal energy of a comoving volume (e.g. a cosmic...

Hi, I am not a cosmologist, but this question has been bugging me for some time. I am an engineer, and I own an aquarium, at least I owned an aquarium with an awesome LED light. Under certain conditions, I found that when the blue night light was on, organics in the water would fluoresce, green...

Does the expansion of the universe affect orbits? Would the orbits of the Magellanic Clouds, for example, be different if the universe were not expanding? If orbits are affected, at what scale do we first detect the effects?

Since there is no privileged inertial frame, I would have expected the first particles in the universe to have no particular bias in their momenta. Relative to an observer I would expect the distribution to be uniform and unbounded. The mean momentum of the initial particles relative to an...

Why did the expansion of the universe cause an increase in the wavelength of the photons that existed during the time of Photon decoupling ? Does this mean that expansion of universe stretches everything and stars that were present when the universe considerably expanded also got stretched?

From the outset let me assert that I am not putting into question the expansion of space. Redshifts and all that. But there is an example which one often reads in popular astronomy articles which appears at first glance to be faulty, although I suspect it is my reasoning that is faulty, and I...

The universe seems to be expanding since the farther away an object is, the faster it is moving. However, because of the finite speed of light, the farther away we look in distance, the further back in time we look. Does that mean that galaxies were moving faster in the past and are now slowing...

Is there any relationship between the Speed of gravitational waves and the Universe's "local" expansion rate? Speed of gravitational waves is supposed to be equal to the speed of light. Gravitational waves don't travel faster than light. But we can observe far galaxies moving away from us with...

Does the presence of the cosmological constant modify the rate of expansion of the universe even during the earlier deceleratingly expanding phase of the universe?

I have read the advice of Nugatory and Jorrie in order to get me started on understanding cosmology; I have played around with the cited calculators (except http://www.einsteins-theory-of-relativity-4engineers.com/CosmoLean_A20.html doesn't open for me), without mastering them, and read for a...

With the LDCM, cosmological constant, model I understand that the scale factor of the Universe grows more rapidly than the Horizon. I believe the correct horizon I need to be considering is the Hubble Horizon and the point when objects recessional velocity hits the speed of light they disappear...

Hello all, Is electromagnetic radiation considered a driving factor of intergalactic space expansion similar to directed energy propulsion? I assume every point in space has countless photons passing through it from every direction at all times.

Is the theory that inflatons become dominate when gravity is strong (as in right after the big band) and when gravity is weak (as in driving the current expansion of the observable universe)?

Hello! I have a question regarding the effect of the accelerated expansion of the universe on the Hubble plot (redshift over luminosity (or distance). I understand that for relatively nearby galaxies, this appears to be a linear relationship but that because of the accelerated expansion of the...

Prof. Brian Schmidt got the Nobel Prize for his work in expansion of the universe which he did in 1998. His team was able to figure out that earlier in the past, the universe's expansion rate was slower than it is right now and it's actually increasing day by day. However, wasn't the same thing...

I just have a quick question about a concept I think I haven't fully grasped from my cosmology course. Why does non-relativistic energy have an equation of state with w=0? Also, is the concept of pressure different in general relativity than in thermodynamics or statistical mechanics?