I understand that a particle with zero rest mass would travel at C, and particles travelling at less than C should have mass. Photons travel at C in a pure vacuum and have 0 mass, but slow down in a medium to less than C. Does that imply that photons traveling through a medium have mass? Even through the very thin interstellar medium light would be slowed down by a tiny tiny amount, so should there be mass attributed to all the light traveling through the galaxy/universe?

I admit I am not studying cosmology or quantum physics, I'm a simple curious engineer poking around outside my wheelhouse. Is this a valid question, or already known and accounted for, or just flat wrong? There are many people much smarter than I researching this field so I highly doubt my dumbass is asking any ground breaking questions from my bedroom, and I'd love to hear any explanations for why this does or doesn't make sense.

Was Einstein's Cosmological Constant, which he called his “biggest blunder”, really considered "confirmed" by the theory of Dark Energy? Einstein used it to explain a static universe in the presence of normal gravity. Modern understanding uses it to explain accelerating expansion of the universe. These seem like different concepts, even though they both include an unexplainable repulsive force.

I'm certainly not qualified to question anything said by Einstein, but it seems like his explanation was based on an incorrect assumption about a static universe. So it seems like a stretch (no pun intended) to say that he predicted Dark Energy - but I hear many science documentaries present it this way.

Adam Reiss and Clifford Johnson give credit to Einstein in this way in a recent episode of Nova on PBS, for example. It's at minute 42 in season 51, episode 8.
https://www.pbs.org/wgbh/nova/series/decoding-the-universe/.

Hi there I’m trying to watch as much things that detail the Big Bang theory the science, the history of the discoveries & the development of the theory over time, any YouTube videos, podcasts, articles, documentaries, episodes or books, if you could link any you have in the comments please thank you

Hi everyone. I just wonder If we know that massive black holes in the center of galaxies have something to do with dark energy, Can the emitted Hawking Radiation from these black holes be the culprit behind the dark energy. This minuscule power will be additive and like an Ion engine, will get faster and faster with time but will not get faster as the Hawking Radiation reduces as the size of black hole gets bigger.

This might sound stupid so sorry for taking your time before hand and thanks for telling what I am missing in my thought process and/or the information that I need to know.

Thanks.

I'm a 16-year-old student interested in a career in cosmology. I'm trying to decide whether it's better for me to pursue my studies in India or abroad.

I fell asleep last night listening to Leanord Suskind on Theories of Everything talk about how string theory may not be a correct description of the world. He said that the universe seems more likely to be De Sitter. I admittedly don’t know what all that means but I was wondering if what he said, which was that there is no edge to De Spitter space, means that there isn’t even an other side for the universe to expand into

There is a recent study strengthening support for the hypothesis that black holes are in fact the source of dark energy.

Should this be the case, then in the far future when every black hole in the universe has evaporated, dark energy would have weakened enough for gravity to begin slowing and subsequently reversing the expansion, therefore ending the universe in a Big Crunch, of which a Big Bang would emerge.

To me this seems to suggest that if black holes are indeed the source of dark energy, then it implies that the universe cyclic, is this correct?

Evidence mounts for dark energy from black holes - University of Michigan

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I understand that standard BB cosmology holds that time began with the universe from a singularity approximately 14 billion years ago.

The thing I’m trying to understand, how can time have begun? Wouldn’t a thing ‘beginning’ require time? As in - from one state to another state requires time?

This leads me to think time must have always existed..

Seems to me the radiation of light across cosmic distances should develop an increasingly broad wave similar to diffraction, such that it might impinge anywhere along a wavefront. I haven't been able to see a discussion of it anywhere.

I’ve skimmed through a few books and pretty much every case (besides the basic recombination stuff) have always set the chemical potential equal to 0.

I recently skimmed over a paper that included an equation with nonzero chemical potential and realized I have no idea what I’d do to find it (the paper was on sterile neutrinos). From basic thermo I know mu=(dU/dN)_V,S but I have no idea how to actually go about computing this.

Are there any resources where I could find more about this?

Conformal cyclic cosmology (CCC) is a cosmological model in the framework of general relativity and proposed by theoretical physicist Roger Penrose.^([1])^([2])^([3]) In CCC, the universe iterates through infinite cycles, with the future timelike infinity (i.e. the latest end of any possible timescale evaluated for any point in space) of each previous iteration being identified with the Big Bang singularity of the next

Let's say dark energy was removed and Universe began collapsing, would we have a giant quasar at the end in which all mass fell into and if so what would this look like?

Let's assume for a moment that the Cosmological Constant isn't defined as Constant. Let's assume that it varies with Cosmological Time:

• Q: Does anyone have a graph of what it might look like ?

I was just reading the Big Think article by Ethan Siegel (just love his stuff!) about cosmic inflation and the Big Bang, and this thought suddenly occurred to me: was our Universe the result of a vacuum energy state (a "false vacuum") decay in a prior universe? (after typing this, I found some older references to the same idea that I'd not seen before)

Ooh, one more crazy speculation: what if the boundary of the "observable universe", about 93 billion light years, is the boundary of the vacuum energy decay progression?

A few months back I attended a lecture which talked about "what could have happened before the big bang". Unfortunately, I don't remember most of it, so I'm usually going by keywords, they said something about the fact that due to quantum fluctuations and the heisenberg uncertainty principle, and if you do the "calculations", you would get to the conclusion that it is impossible to measure time before the big bang, because of the the error term in time, you wont ever be able to tell what "time it is". They said the math was boring, however i wanted to look at it and also possibly get to know more about it. Can someone elaborate more on it?

Hi everyone, I’ve been thinking about an idea and would love your thoughts. I'm new to this forum and looking to better inform myself.

What if dark matter and dark energy aren't separate entities but instead arise from interactions between quantum states of matter, photons, and the underlying structure of space-time? For example, could they result from transitions between quantum and classical behaviors as space-time adjusts to different degrees of coherence or decoherence?

I’m wondering if viewing space-time as having "layers" where quantum effects gradually shift into classical ones could offer a new perspective on these phenomena. Could this help explain some of the effects we currently attribute to dark matter and dark energy? I have tried to fit this into an overall framework, but I'm not an expert by any means.

Any thoughts or critiques would be much appreciated—thanks in advance!

I know it's a fact, but wondering if general relativity or other thinkings of his would be able to explain this?

Im just an enthusiast trying to understand the different theories. I was just wondering if the heat death scenario allows for an infinite existence, even if most of it is spent in a "heat death" state.

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I'm just some dummy but my very lay understanding of the situation is this:

Statistically speaking there almost must be aliens out there somewhere. Yet despite lots of searching, we have no evidence of them anywhere. (The Fermi Paradox.)

Despite knowing this, I find the topic very fascinating and would like to learn more about, for example, the types of things we've tried (I know about the Dyson Sphere hunt, for example), the types of things that have been suggested but not yet tried, what we might have learned from our findings (even though we haven't found evidence of aliens), if we've narrowed down the most likely candidates for specific planets that might contain life, what the current best thinking of the "explanations" for the Fermi Paradox might be, that kind of stuff.

Does anyone have any recommendations?

I posted here before on some spiritual bs but now with my further knowledge on the way tunneling/fluctuations works is that they are random and that (in very rare circumstances) tunneling could happen from states of low to high energy. So could it be possible that given an exponentially long time (abt (10¹⁰)⁵⁶ years we could we could see another big bang?

Hello all,

I am a physicist that works in magnetism, however I am part of journal club that is looking at all branches of physics and it's mu turn to present.

I found a paper that began by saying that some JWST observations of early galaxies (z~15) appear to be about 10 Gyr old based on how much they have evolved. However, according to their redshift and the LambdaCDM theory, they should only be 0.5 Gyr old. Clearly there is something wrong with one of the models if the results are off by that much.

Is this a big problem in Cosmology/Astrophysics? By that mean:

• Is it foundation shaking and we need to rethink all of our models?
• Or is it just interesting and could lead some some developments?
• Or does nobody really care?

Just trying to get a feel for the impact of these observations. Any helpful discussion or links would be appreciated.

Thank you!

Hi everyone, I've been putting together a list of the most influential research articles for modern cosmology. What do you think? What am I missing?

EDIT: Added Vera Rubin, Gamow et al., Leavitt et al., COBE/WMAP/Planck teams, James Peebles, YB Zel'dovich

I was just watching a documentary about the space and it said there about another big bang slowly happening (not anytime soon), just wanted to ask to see if there is gonna happen anytime in life (talking about like millions of years)

There's an excellent paper that I've read a few times called "Expanding Confusion" (2004) by Davis and Lineweaver that explains the variety of cosmic horizons quite well. Link to it here.

However in section 4.2 of that paper, when they derive a special relativistic and 𝑣=𝑐𝑧 interpretation for cosmic redshift (and disprove the SR interpretation by 23 sigma), it seems there are potentially some calculation errors: I'm unable to reproduce their results for the apparent magnitude in the B-band 𝑚𝐵.

Writing their method out explicitly we have Hubble’s law:

𝐻=𝑣/𝐷,

which is added to the longitudinal relativistic Doppler shift in terms of velocity,

https://preview.redd.it/3tze4tkzf5wd1.png?width=598&format=png&auto=webp&s=3dc8a84fcd4781cfeba421d385f54747c6d8e394

like so,

https://preview.redd.it/apfvd202g5wd1.png?width=682&format=png&auto=webp&s=5601af76cfc98307c36ab7bce9a0e8e513abad56

Then this proper distance is converted to luminosity distance, 𝐷(𝑧)(1+𝑧)=𝐷𝐿(𝑧), whose value we then plug into the distance modulus they used:

https://preview.redd.it/7ue8vfg4g5wd1.png?width=886&format=png&auto=webp&s=30c81ee6354caedfc58293a2710cff52d375ff61

where absolute magnitude 𝑀𝐵 = -3.45.

In the v = cz case, they use this for luminosity distance and put it into the same distance modulus above to get their measurements:

https://preview.redd.it/ylwlyva5g5wd1.png?width=672&format=png&auto=webp&s=ffee576d347f08420cae1cb0b3314a110abee46a

The errors become clear after a quick calculation: if we input 𝑧=1 and 𝐻=70𝑘𝑚/𝑠/𝑀𝑝𝑐 for instance, we get 𝑚𝐵=24.33 for the SR interpretation and 25.44 for the 𝑣=𝑐𝑧 interpretation rather than 𝑚𝐵=22.83,23.94, respectively, as written in the paper. I've put the corrected magnitude-redshift curves into their original Figure 5.

Did I misunderstand something or was there an oversight in their paper?

https://preview.redd.it/cmg6htk2f5wd1.png?width=2228&format=png&auto=webp&s=61bf785ac78e07d0e2eb2caad900c01623e35474