r/astrophysics

I am quite comfortable with the notion that the universe is infinite, and that the early universe (during/right around the big bang) was also infinite.

But I am confused by how we can say that the universe was infinite and that matter in this infinite universe was uniformly spread out. Wouldn’t this imply that there is an infinite amount of matter in our universe also? This seems to be contradictory.

Any finite amount of matter in an infinite universe either needs to be non-uniform and clumped, or infinite which allows it to be uniformly spread. The uniform spread of matter seems to be well tested with CMB observations and Baryonic Acoustic Oscillation measurements. But infinite matter seems to be a blaring contradiction to reality. Is there anything I am misunderstanding? Anything else I should research on?

Hi! I work in data science and we have this thing at work where we get to showcase an independent project related to data science (unrelated to the actual work we’re doing) and I wanted to do something related to astrophysics.

I was of thinking doing something where I analyse certain astronomy related datasets and do stuff like classification/clustering/forecasting etc. depending on what the data calls for. I could also take up some new data analysis-related technology that’s not that well known and explain how it works and apply it to a real-world example.

I would love some suggestions on what I can work on! :)

https://preview.redd.it/10jjttkrrb2h1.png?width=755&format=png&auto=webp&s=5176a6776efc89b32f9ba6eeb5120a4b9492892e

I understood the 2.14's first and third equations' derivations, but I still couldnt figure out second equation, cos h cos d one.

can someone please explain?

Since we have these huge telescopes and can look back in time even see the cosmic background radiation why don’t we see where the universe started?

Any explosion has a center. Even atomic bombs in space expand outward in a sphere. So why do scientists say the universe is “flat”?

Is it flat like a sheet (---) but so enormous that it looks round to us because we can see stars in every direction out to about 13 billion light years away?

And also, any explosion fades at the edges — there’s usually less material at the outer edge than near the center. Couldn’t we just find where matter is densest and assume that’s the center of the universe?

Imagine you were inside an atomic bomb explosion in space about one minute after it exploded. If you looked around, you could probably tell where the explosion started, because the center would still be hotter and denser than the outer regions. The explosion would look spherical, not flat.

And then there’s the question that seems to make astrophysicists mad:
what is the universe expanding into?

If the singularity started somewhere, then wasn’t there already something outside it? Or not?

I don’t understand why scientists don’t try harder to solve or explain this.

Would an extremely powerful telescope for example, one placed on the dark side of the Moon be able to look back so far that it eventually sees just nothing?

And have we already observed stars or galaxies at the edge of the observable universe fading away because they moved so far that their light can no longer reach us?

Shouldn’t this be happening constantly in deep field images? Could a long series of deep space images, like a GIF over time, eventually show a galaxy disappearing?

No idea on the math or idea of it but similar to Black Dwarfs, maybe they take forever to form because they cause space to warp in such a way that time slows down when you approach the epicenter? Or maybe it's because they're made up of Strange atoms, formed when clusters of Strange atoms become large enough. That's my only thought, again I know very little on the topic but eventually I plan on getting an Astronomy degree.

https://preview.redd.it/sygy1ksn992h1.png?width=907&format=png&auto=webp&s=ad7f2b6c6282c8d83afeeb83cac5c4bcf6b7de08

in my opinion, the angles are complied wrong(in my mind ofc), I thought plumb line should create an angle of q that q equals arctan(a^2*y/b^2*x), and angle j should be arctan(y/x) instead, but from what I see and understood from the book, the reverse of my statement is written, can you please help me to understand these?

q is the (fi)', j is the fi btw.

What is that one thing which you found out about the laws of physics or how universe behaves that has left you startled?

So I've been going down a rabbit hole on time dilation and somewhere along the way ended up with what I think might be a legitimate experiment concept. No physics background, just followed the logic until it stopped breaking. Wanted to see if anyone here could find where it falls apart.

The basic idea is a minimalist probe no crew, no life support, stripped down to just a power source, a recorder and a transmitter. Instead of accelerating it linearly to near light speed which is obviously way beyond anything we can do it spins in place fast enough that the surface velocity approaches relativistic speeds. Time dilation doesn't care about direction just velocity so the effect should still apply while the probe stays stationary.

For power it would use Mercury orbit as a charging phase first. Nine times the solar intensity of Earth plus nuclear means you're not carrying fuel for the whole journey and you're not depending on solar once it leaves the inner system.

The cage is the part I'm least sure about. A separate outer structure counter-rotating around the probe with no physical connection between them held in relative position by the opposing angular momentum. Takes the particle bombardment damage while the probe stays intact. No attachment means no junction weak point.

The transmission is the actual experiment. Continuous telemetry including onboard clock data compared against a stationary reference clock on the ground. Instead of confirming time dilation happened after the fact like existing atomic clock experiments, you'd be watching the divergence accumulate in real time from both sides of the temporal frame simultaneously.

Main problems I already know about: materials don't exist yet that survive the rotational stress, spin-up energy requirements are way beyond current tech, and the signal decoding from a relativistically rotating transmitter is unsolved. So yes it hits the same wall everything hits right now. But the physics itself I can't find a hole in.

Can anyone tell me where this actually breaks?

HELLO this is my third time posting this question to yet another subreddit (when did reddit get so hard to use? 🥲)

So I recently played this game (which was SO good!) called Project Hercules - its an educational game that teaches you astronomy and how to do things like basic photometry? I really enjoyed this but its not really related to anything I do in real life, and I don't own the materials to do this by myself. Is there any way that I can do this in real life? like volunteer to figure out the distance and heat or classification of stars - or do something online using pre-existing data that just needs to be sorted. Might be a silly question but I thought it might be worth asking

I'm aware that the atmosphere acts as a conductor for sound but why is it so conspicuously absent?

I really don't understand that. In the void of space there are a ton of particles originally just hydrogen and helium that started piling up together.

How do those clumps of rock and dust combining together allow sounds to exist​​​

Can sounds be heard inside a planet or a star or around a black hole? How and why it exists if space doesn't allow it to travel confuses me. ​

I’ve always loved the universe and how it works. I’m currently a junior going on to senior year and I’ve decided I wanted to study astrophysics when I go to college. The thing is though, I am pretty bad at math. My sophomore year I actually did really really well in it, and my teacher was one of the best ones ever. However, this year was my first time doing honors classes and I got put in an honors math class. I really struggled, and averaged a C or even a D in most tests/quizzes which led me to have to retake them every time. I have a high B in that class and it’s the only B I have (all my other classes are As)

I feel really discouraged because I know for becoming an astrophysicist you need to have a strong foundation in math, but I just can’t seem to grasp some concepts as fast as my other classmates. I don’t know if it’s fatigue from junior year, but I feel really dumb compared to other people. Not to mention my CAASPP scores came out, and even though I got a 4 in English and a 3 in science, I got a 2 in math. I feel really sad and like I am not going to be able to pursue becoming an astrophysicist in the future. Any advice??

Edit: The comments do help. Some of them are a little bit discouraging I do admit, but I am willing to work as hard as I can so I can get good at math. Obviously if this doesn’t work out I do have a plan b (and c and d) lol. But overall the advice is really helpful so I appreciate that. Btw, I saw some people say that I don’t really know what astrophysics truly is, but I do. I know it’s basically a whole other branch of physics combined with applied math, and to understand it you have to have a strong understanding of what you’re doing. I really love math even though it frustrates me sometimes, so I really have no problems having to dedicate hours of my life studying it. Thank you again for the advice and replies.

I am looking for quantum physics books online for my gf’s birthday (or other natural sciences, could include chem, biochem, and electrical chem, or electricity as those are all her interest) and I want something that has good explanations and what not. Not too school-like. When I try to research into it, I feel like the description of the book is over-exaggerating how good it is. I was wondering if anyone had any personal favorites that helped them grasp difficult concepts in natural sciences? Thanks for any help!

I made a post earlier asking about people’s grad school experience and a question came up of what I’d study specifically. I was wondering if I could get help on ideas or recommendations of what seems to suit me best?

I love astrophysics and space but I don’t really enjoy coding which is know can be a big part of that. I’d rather theoretical subjects on paper. Subjects like I said with space, gravity and such really peak my interests. If you could maybe ask questions to see what my preferences are, I just feel kind of lost on how and what to pick or orient towards.

From the article:

Scientists at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory have uncovered experimental evidence that particles of matter emerging from energetic subatomic smashups retain a key feature of virtual particles that exist only fleetingly in the quantum vacuum. The finding offers a new way to explore how the vacuum—once thought of as empty space—provides important ingredients needed to transform virtual "nothingness" into the matter that makes up our world.

This experiment has been interpreted to suggest virtual particles are “real” particles. This causes a problem though because virtual particles don’t have to satisfy energy conservation. The explanation has always been that virtual particles wink in and out of existence at such short times scales, ca. 10^-21 and shorter, that they can not be measured.

But I’ve always been ill-at-ease with this explanation. The reason is under special relativity, the time they exist can be made longer if the system is moving fast enough. Consider then, the highest Lorentz time dilation factor we can reach with our proton accelerators is ca. 10,000. But the highest energies observed with ultra high energy cosmic rays, UHECR’s, is a million times higher than our accelerators, corresponding to an equivalently higher time dilation to reach a dilation factor of 10^10. This means we would observe the existence times of the “virtual particles” arising from UHECR’s at 10^-11 s, or 10 picoseconds. This is well within the measuring times we’re capable of. In fact, the explanation of anomalous effects we observe with UHECR’s may be due to those “virtual particles” being measured as real:

https://www.google.com/search?q=anomalies+of+uhecr.

And using the fastest timing equipment we now have, we might not even have resort to looking at UHECR’s. Agostini, Krausz, and L’Huillier won the Nobel Prize in Physics in 2023 for creating methods of measuring events at attosecond times scales, 10^-18. Then at our highest particle accelerator energies generating time dilations factors of ca. 10,000, virtual particles existing at 10^-21 seconds, would be observed by us to to last 10^-17 seconds, 10 attoseconds.

Another intriguing approach is from measurements of quantum tunneling. Some experimental results suggest this might happen at attosecond times scales rather than happening instantaneously as previously thought. Then measurements of quantum tunneling in accelerated systems to 10,000 time dilation factor would bring that time down to the 10^14 second, 10 femtosecond range. This is within the range of time measuring devices already present at our highest energy accelerators.