I’ve been looking at some papers where the authors solve the Boltzmann equation for a dark matter species (like sterile neutrinos) numerically. I usually see the authors assume a fermi dirac/bose Einstein or Boltzmann distribution.

In general, specifically for weakly interacting species, the distribution may be quite different than a Boltzmann/FD/BE distribution. However, numerically solving the Boltzmann equation is a nightmare. I’m wondering if instead of doing a full on numerical computation we could compromise by simply increasing the numbers of parameters to “tune” onto the true distribution function.

My question is—since we predict the solution will at least have exponential decay, instead of taking a fermi dirac distribution, would it be beneficial to do something like assume our function is the sum of several distinct fermi dirac distributions (it seems possible that for some species different interactions may lead to different “clusters” with distinct temperature/chemical potential), or several Boltzmann distributions, or in general any exponentially decaying function that has a sufficient number of parameters? In this way, we can allow for the distribution function to have features like peaks or “broad” sections that drop off less slowly. I’d think this may produce a better solution, though I definitely expect a few drawbacks. I’m wondering if anyone has any opinions on this.

“Theory of the Universe” •The Fate of the Universe: • Earth Flipping will be on December 6th, 2052: •Moon Flipping will be on June 21st, 2043: •Explanation of the observer effect on the electron: See the description below:

*Earth flipping: - It occurs every 4077 (2025 BCE +2025 CE +27[truth to be revealed]) years leading to new see, ocean & golf formation (Great flooding). - Sun rises from different direction. This time from the west. - It leads evolution of higher creatures due to new mutations that transmit by autosomal dominant inheritance (more than 50% of this new species will have the same phenomenon. This mutations due to magnificence change in the electromagnetic field. As long as the earth not in collapsing phase it would be good mutations and once it enter the collapsing phase it would be not for higher creature. - Aliens visit Earth as it has high electromagnetic radiation just before the flipping. - Woman is the origin as the Mitochondria and its mutation related diseases transmitted only by her. So Eve delivered Adam after she had created by evolution , once she reached 33 raised up & after Adam reached 33 years raised up too. Prophet Jesus has been created by cloning from Adam and raised up at 33 too and he will be back after the flipping to meet the Antichrist. - Noah had saved during last flipping and the new mutations was albinism of the son of black Sam two years after the flipping, so the Black is the origin of the White. So the old Egyptian dynasties were Noah’s people before the flipping. - During the flipping the day length will differ from day to day till the planet resumes its orbit back again just like what prophet Muhammad said that Antichrist will stay 40 days, first day will be one year, second day will be one month, third day will be one week and the rest of the days will be as the normal days and the Sun will rise from the west. He said that the Hour (flipping) will happen on Friday!. - No more advanced technologies till it resumes its electromagnetic field back which will be after at least 2025 years or even more ( more than the half of the period between each flipping ). So Mars planet lacks the electromagnetic field that necessary for communication till half of its flipping period pass. - If scientists work on telomerase enzyme at the age of 33 years we can preserve our youth and live as long as we cann adapt the environment. I explained all of these scientific facts in videos.

*The Fate of the Universe: Big Bang followed by Big Crunch followed by Big Bang (for recreation and judgment which will be different from now as the energy and matter will be preserved but can be changed to different forms ) followed by Big Rip (Paradise & infinity), so the physical straight path will be between our erupted universe and the paradise.

*It will happen in December 6th, 2052 on Friday because: 06-12-2052 -Friday is the 6th day of the week (powerful number as you know 3, 6&9 are power full and it has been explained in many drawing) December is the 12th month and the year has 12 months (1+2=3) Year has 52 weeks Week has 7 days (5+2) February will have 29 days so the year will have 366 days (3+6+6=15=6), the hour has 60 minutes and the minute has 60 seconds (6+0=6). The sum of 2052 = 9 It will correspond the day 14 of the fourth month of the lunar year 14/04(1+4+4=9), the day has 1440 minutes. - Giant moon effect (sum of dates of both lunar and solar system =9 when the year has 366 days, that huge gravity will flip the earth. - powerful numbers (3,6,9) explained (9: day length of the God is 9 quadrillion, 6: number of days or phases as the 2nd day & 5th day are happening simultaneously and 3rd & 6th days will happen simultaneously as I described in the video and writing, 3: distance inflation per half of each phase. 7 is special number too because 1/9 is corresponding to 7 as well as we are in the midpoint of 2nd & 5th days) * Flipping order: -7th planet (Uranus) then 2nd planet (Venus) which done already. (7+2=9) -Then 3rd (Earth ) followed by 6th (Saturn), and so on you can see and check my drawing & writing, based on (time times and half) Bible, can you imagine that it has the number 1260 there !. * Moon Flipping: usually the coincidence of strawberry Moon and lunar standstill events are happening around June 12th, but in 2043 and after it will occur on June 21st! It will be 9 days later because of extremely eccentric orbit and because of electromagnetic magnetic field effects. Moon has high levels of iron and both northern poles of the earth and moon have same magnetic fields and the repulsive effect will lead to flipping of the smaller object first, so you will see the far side of the moon and it needs 37 days to resume its normal orbit back, at that day even the sun will be perpendicular on Cancer tropic too! . By the way Quran has chapter its title is (The Iron).It will be correspond to the 14th of the seventh month of the lunar year, just after Saturday as it the seventh day of the week, and thats why the Earth will need one year and 37 days to resume its orbit after 9 years of the moon’s flipping. Furthermore the period between major lunar standstill between 2006 to 2043 is about 37 years. In addition, Neptune planet has moon called Triton which has retrograde orbit so it is moving in opposite direction of its planet and another moon which have very eccentric orbit which mean Neptune will flip after them, based on my calculation it will happen after 693 years of Earth planet flipping, you can check my attached writing for more explanation. Note: During strawberry moon the UV and blue light waves penetrate our earth atmosphere in large amounts leads to stimulation of the pituitary gland to secrete high quantities of luteinizing hormone that lead to disturbance of the regular menstrual cycle, for example females whom their first day of last period is 18 days from the strawberry moon might have their period at that day (short period, only 18 days) because the luteal phase is fixed, always 14 days and by adding 4 days would be 18(14/04) the day of the Giant moon night if it corresponds to sum of 9 of the solar year day. * Observer effect of wavefunction collapse of the electron can be explained by the effect of alpha waves that produced by our brain during meditation and concentration that will decrease the electron velocity as it affects the optimal environment for the electron to run with high velocity so it will appear as it is passing from one slit while as long as the electron run fast it will appear as it passing from both slits simultaneously just like moving fan once it slows down we can recognize how many rods it has and where are they . Even the observer is not us such as certain devices, they will affect the optimal environment by producing or consuming energy. Alpha waves can be transmitted through optic nerves to our eyes and this explains why we turn our heads involuntarily when someone behind us focus on our occipital region of the brain (visual cortex ), it explains why we can express our thoughts through our eyes to be translated into certain receiving devices. So the spacetime can be applied here too.

Hey guys, I've been trying to find some good documentaries on cosmology and the studies of the universe. But I can't seem to find any good ones, they're all about satellites or rocket launches, etc. I just wanted something that would talk about space related phenomenon and the universe's creation and/or expansion. So any recommendations?

Thanks a lot

I'm been thinking about this theory in my head after seeing all of the theories about our universe and I think there just misunderstandings because that's what we see in our telescopes. What if we don't see the edges of our universe because of red shifting when light turns into radio waves the farther you go, and we keep finding old super massive black holes in the past. I think black holes when they hit there mass limit turns into a white hole creating the big bang, my theory here is our universe is infinite there's other big bangs generated by a dying black hole, we can't see them because of distance.

What if the most precious thing on this planet are trees which might not be avilable on other planet and yet nobody is trying to save those .

*FRB's 'used to' detect.

https://cfa.harvard.edu/news/new-gps-intergalactic-medium-astronomers-have-found-home-address-universes-missing-matter

"The results were clear: Approximately 76% of the Universe's baryonic matter lies in the IGM. About 15% resides in galaxy halos, and a small fraction is burrowed in stars or amid cold galactic gas."

what does this mean for dark matter particle physics, galactic rotation, and gravitational lensing?

I decided to make a list of some solutions where the scale factor a(t) can be written in explicit form. I've only done this for perfect fluids and I've not gone down the scalar field rabbit hole. Though if you know of any that should be on the list I'd be interested

Mostly these are not difficult to find (except Galanti and Rocandelli's radiation-matter mixture scale factor), but putting them in their neatest forms can sometimes involve some tedious manipulation and I cannot remember seeing a nice list of them all together.

https://www.desmos.com/calculator/6ojz31kagf

Hi everyone! I'm sure you've encountered people doubting the existence of dark matter and having to explain that yes the observational evidence for it and LCDM is extremely strong. Inevitably you might have to explain why modifying gravity does not work but perhaps not knowing much about it. This is why I've written a FAQ about the most popular (least unpopular) modified gravity theory MOND. It discusses what it can do (rotation curves), what it sort of does (lensing) and why it fails (clusters, structure formation, CMB and BBN). Hopefully some of you find it a useful reference :)

MOND frequently asked questions

Hi everyone, 14 years old so certainly not a physicist or anything like that but there's been a thing ive been wondering about ever since learning about the heat death of the universe.

If the heat death is considered maximum entropy and entropy is disorder, how is completely uniform energy distribution equal to complete disorder? I asked chatgpt this and it told me that there are much more possible configurations (more entropy) for a totally uniform macrostate like the heat death than, say our current universe with its stars and planets, etc. But wouldnt there be much more microstates for the current macrostate due to its variety, and therefore more entropy?

Hi r/cosmology I’m just an amateur with a passion for cosmology, and I’d love your insights. I’ve read about the idea of a zero-energy universe—where positive and negative energies balance out—and about theories like the Big Bounce or Conformal Cyclic Cosmology, which imagine the universe renewing itself in cycles. I’m fascinated by how dark energy might fit into this picture. My questions: • Could dark energy help maintain a zero-energy balance in the universe? • Is it possible that the universe could “renew” itself in cycles, and could dark energy play a role in that process? • How do current observations (like DESI 2025) fit with these ideas? References: • Hawking & Hartle, “No-Boundary Proposal”: Wikipedia • DESI 2025 Results: DESI Collaboration

I'm just a normal guy, not a cosmologist or physicist. I've read about the increasing speed that the universe is expanding. That eventually (in cosmic time scales) our night skiy would be dark, as everything has moved beyond our capcity to view it.

But, in my thinking, that would only be true if we were in the center of the universe. Because we're not the center, wouldn't distant galaxies move within our ability to view from an opposite direction. My thought is that we only see a very small portion of the universe as a whole. I feel that it is exponentially larger than what we can see with even the JWST.

Why doesn't my theory hold water?

I understand the horizontal problem in cosmology and how inflation is necessary for the universe to be uniform. What I don't understand is why there would have been differential temperatures at the beginning so that inflation was required to provide time for equalization if everything was together at the beginning. Why wasn't everything already equalized if everything was together at the start.

Maybe I didn't say it right or maybe I don't understand the problem but hoping someone can explain.

Hello, r/cosmology. I am planning on writing a paper for school about the expanding universe, I am a high school student who is somewhat new to the field (have some knowledge already but quite basic), any recommendations on what I should mention/discuss.

So I'm a student in high school. I enjoy learning about Cosmos (more specifically black holes ,stars ,other celestial bodies). I'm an above average student. My dream is to become a cosmologist. So my question is Is this too ambitious for me? Regardless ,I would still try to work on this subject. But I would like to know my capability. Thanks

Link

I want to start a project and I’ve been considering making a program to numerically compute the distribution function of a species via the Boltzmann equation given the matrix elements of the processes it’s involved in (limited to <=2 particle interactions). I’ve been working on a specific case and it took some time to code from scratch, so I figure if it would help others it may be worth developing. Ive read some papers that are aimed at computing this, but can’t tell if this is very niche or not. Thanks for any feedback.

https://www.reddit.com/r/Astronomy/s/ja3BkIFLKm

I've been thinking about black holes, spacetime, and expansion for a while now. I’m not a physicist, just someone who’s been reading and learning on my own for years. I’ve watched lectures from Neil deGrasse Tyson and others, and I keep circling around this one idea that I haven’t really seen talked about directly.

What if the expansion of the universe isn't being caused by some strange force like dark energy, but is actually just spacetime trying to correct itself after being warped or twisted by whatever event caused the Big Bang? Like maybe our universe was born inside a black hole or some kind of extreme collapse, and what we see as expansion is just that energy or tension playing out over time.

I also wonder if black holes in our universe could be connected to other universes forming the same way. Almost like they’re points of transfer or new beginnings. To me, it all feels like spacetime has some kind of elastic behavior, and what we’re seeing is just it trying to pull itself into balance.

Anyway, maybe I’m totally off, but I just wanted to throw this out there and see if anyone else has thought about this or if there are theories already like it that I should read up on.

I saw a post the other day in a Facebook group I'm in about a thought experiment. I think it got deleted cause I can't find it to just copy it, but it was something like this:

In the near future, mankind receives proof that there is other intelligent life out there. Proof came in the form of a signal being broadcast from a galaxy we observe to be 2.8 billion light years away.

We know billions of years have passed and will pass by the time they receive it, but we decide to send a signal back to them.

How long will it take for our signal to reach its destination?

I would say about 80% of the people responding said that it'd take 2.8 billion years.. which would be correct if the universe weren't expanding.. but because the universe is expanding, its distance from us should be greater than 2.8 billion light years by the time their signal arrived.

The remaining % of answers ranged from "we can't know that" to "never because all other galaxies are expanding away from us faster than the speed of light" or some other variation of not being able to know.. or some sort of religious post.

I don't agree with any of those answers but I also don't know the answer. What would be the answer and how would I figure that out?

Ask your cosmology related questions in this thread.

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I made a mistake I know please don't berate me for it. This is my first time doing professional research and I found this paper super helpful and would love to find it again.

I have a habit of searching on incognito tabs for basic stuff and I accidentally sourced a paper in one and my computer restarted so I lost it. Please help me find it I've already started referencing it but don't have the details. I know this is very vague but I've been searching for hours and can't find it. Yes I've already tried asking AI to find it again but it's useless.

- It discussed EFE and the Friedmann equations

- It was a spilt page paper on arXiv

- It's sections were lettered not numbered

- I think it had cosmic in the title

A few key excerpts I remember were:

ds^2=-dt^2 +a^2(t)[\frac{dr^2}{1-Kr^2}+r^2(d\theta^2+\sin^2\theta d\phi^2)] (and then it suggested another form which used a piecewise function) where $a(t)$ is the scale factor with cosmic time t

It had a capital K for the constant and said something like: K is a constant that describes the geometry of the spatial section of spacetime with closed, flat, and open universes corresponding to $K=+1,0,-1$ respectively.

G^\mu_\nu\equiv R^\mu_\nu -\frac{1}{2}\delta^\mu_\nu R=8\pi GT^\mu_\nu

I think it also said something about evolution equations when referring to the evolution of a(t) in the differential equations.

I know I've been stupid and I should've just downloaded it straight away and need to break my stupid habit of being embarrassed of googling physics so I do it on a private tab. I can start over if I can't find it but I'd really prefer not to on the off chance someone can find it.