/r/Physics

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For physicists and physics students. See the rules before posting, and the subreddit wiki for common questions. Basic homework questions are not allowed.

/r/Physics is for physicists, scientists, graduate and undergraduate physics students, and those with a passion for physics. Posts should be pertinent and generate discussion.

See the subreddit wiki for information on using LaTeX, related subreddits, and links to previous discussions on common questions.

You can choose a user flair by using the 'edit' option next to your username above, and you can join the subreddit Discord here.

Encouraged submissions

Open-ended discussions
  • Debates and discussions on all topics related to physics are welcome. Please make an effort to engage the community rather than simply stating your views.

  • Closed-ended questions which are more straightforward to answer will get a better response in /r/AskPhysics.

Academic publications
  • Links to papers in physics journals (free or otherwise) are welcome. Pre-prints are accepted, but moderators reserve the right to delete any posts that break the rules regarding unscientific content.
Science journalism
  • We invite links to all websites, but article and blog post submissions require proper sourcing from the literature or mainstream scientific journalism. The lack of quality sources is grounds for removal at moderator discretion.

  • If you are posting a link to your own website, please familiarise yourself with the global rules on self-promotion.

Encouraged in weekly threads

Closed-ended questions

Careers questions

Education questions

Textbook/resource requests

Discouraged or not allowed

Homework problems

  • Questions that are specific homework problems or calculations should be redirected to /r/AskPhysics or /r/HomeworkHelp. Neither asking nor assisting with homework is allowed here.

  • Alternatively, try Physics Forums instead.

Unscientific content

  • /r/Physics is for the discussion of valid and testable science, not pet theories and speculation presented as fact. We aim to be a welcoming place for both academics and the general public, and as such posts with no basis in mainstream physics are not allowed as they might serve to misinform.

Sensationalized titles

  • The title of your submission should accurately reflect its contents. If in doubt, use the title of the original research.

Low-effort image/video posts

  • Off-topic images, videos, or otherwise "zero-content" submissions are not allowed. Consider posting to /r/PhysicsJokes, /r/PhysicsGifs, or /r/ScienceImages instead. If you make an image/video post, you should make a comment in the thread describing the relevant physics, linking relevant literature, any computational methods used, etc. This will serve to generate on-topic discussion, and separate your post from low-effort spam. For more information on rules related to these posts, please see this thread here.

Duplicate posts

  • Please make sure that a submission on the same topic has not been posted already.

  • New findings are always reported by multiple publications, and the fact that a specific link has not been submitted does not mean that this topic is not already being discussed on /r/Physics. Feel free to provide links to additional sources in the comment section instead.

Weekly schedule

All threads are posted at 9am EDT (1pm UTC).

Day Post
Mon What are you working on?
Tue Physics Questions
Thu Careers/Education Questions
Fri Resource Recommendations

/r/Physics

2,530,377 Subscribers

167

Why do neutrons have such a short lifespan compared to a proton?

53 Comments
2024/03/20
11:07 UTC

6

Physics Questions - Weekly Discussion Thread - March 19, 2024

This thread is a dedicated thread for you to ask and answer questions about concepts in physics.

Homework problems or specific calculations may be removed by the moderators. We ask that you post these in /r/AskPhysics or /r/HomeworkHelp instead.

If you find your question isn't answered here, or cannot wait for the next thread, please also try /r/AskScience and /r/AskPhysics.

16 Comments
2024/03/19
13:00 UTC

344

If gravity isn't a force, then why does it "need" a boson?

GR says that gravity isnt a force, but rather an effect of curved spacetime. So if gravity isn't a force why must there be a boson (graviton) to mediate it?

If my understanding is wrong, please explain why some physicists seem to think that GR and QM must be unified in order for our understanding of the universe to be correct.

176 Comments
2024/03/19
11:40 UTC

33

Fun physics/science books that aren’t for the sole purpose of academics?

I love watching shorts/reels of random physics facts (particularly of space) but I’m more interested on the observations and not the exact theoretical calculations of how we got there(I don’t mind a little of it)

I’m not good at reading really complicated writing so something dense with information but not written super complicated would be preferred.

Does anyone have suggestions?

(Also physics isn’t something I’m interested in seriously, just something I’m a bit more curious about so that’s also why less calculations would be preferred.

And I did say my preferences but I’m not opposed to anything. Even academic textbooks I’m open to but it’s just not my first pick but if you seriously think it’s really interested I’d give it a go)

35 Comments
2024/03/18
13:48 UTC

3

What are you working on? - Weekly Discussion Thread - March 18, 2024

Hello /r/Physics.

It's everyone's favorite day of the week, again. Time to share (or rant about) how your research/work/studying is going and what you're working on this week.

3 Comments
2024/03/18
13:00 UTC

385

Starting Physics degree at age 29 as a nurse?

Im 29, I have a degree in nursing and working at oncology-radiation unit.

At age 18 I had no idea what to do with my life, so I studied mathematics bsc, but I didnt finished it (ive done 4 semesters out of 6). I was good at it, good grades etc...but I was an idiot and dropped out of uni to work and have money for parties...

Later I did the nursing bsc as I like working with people and it was one of the cheapest programs.

I like my job, but its just not enough. Ive spend the last 2 years reading and studying physics. I love it!!

So: What are your opinions on starting a physics bsc (3 years program) at age 29 as a nurse? (Then a 2 years program msc to become a radiation physicist).

136 Comments
2024/03/17
16:16 UTC

99

Impression of Biophysics

Hello all, I just wanted to comment on biophysics as a bit of a niche and misunderstood field, and what you can expect as a pure physicist working in this field.

I researched in biophysics for 3 years as an undergraduate and helped publish 2 articles and 1 textbook chapter, and I learned a tremendous amount about research in general and how physics and mathematics can be applied to anything when you really study it rigorously. I'd like to encourage physics students to look into applied fields that seem to be unrelated to physics, because they are far more related than you may imagine.

Our group was on the cutting-edge of technology and research because of both how we used technology and took advantage of biological research, and how we interpreted it from a physicists mindset. I was always someone who was purely of the physics mindset, but this made me realize you can delve into biology, chemistry, literally anything and you don't need to be an expert...you will learn enough along the way, its your expertise in physics that allows you to look at these fields in a unique way.

What we would do is receive samples of cells that expressed certain proteins, often ones in the human brain like serotonin receptors or dopamine receptors. These were usually yeast cells that were genetically altered to produce these receptors. They would then be treated to attach or "tag" these receptors with fluorescent proteins, originally derived from jellyfish.

So what you had was a way of tracking the location of the dopamine and serotonin receptors, and you could put these cells in a lot of situations that mimic the human brain.

We would then shoot an incredibly precise and powerful laser at the sample. The best way to penetrate into tissue is to use red light, but the fluorescent proteins would accept green or yellow wavelengths and then re-emit a lower wavelength. That reemission, or fluorescence, is how we detected where the proteins are. However in order to penetrate the sample properly, a red laser would be used with nanosecond pulses, such that two red wavelength photons would be emitted in succession and easily penetrate, and then essentially recombine into a green wavelength photon in excitation of the fluorescent protein. It literally is unreal, how that is possible, and there's a lot of math behind how it works.

As a physicist we had to understand the implications of the research in medicine and biology and understand and deal with the biological samples, but the real work was in understanding the data and perfecting the system, which even came down to quantum mechanics in how the fluorescence worked through resonant energy transfer and dipole-dipole coupling. However, we would end up looking at the locations of the proteins in real time, with live samples, and seeing where they were located in the membrane. This taught us that in actuality, protein interactions are way more complex then we originally imagine, because they form complexes. This effects how they operate, and is stimulated by the environment. For example, serotonin receptors can form complexes in the cell membrane of 2, 3, 5 and even 7 proteins and actually behave differently as a result in how they accept signals and then transmit a signal down the cellular pathway.

It's very complex to describe, but stuff like this requires physicists and mathematicians and computer scientists to take an interest, if we ever want to fully understand how the human body or brain works. I hope that people going into physics don't shy away from strange problems or interesting applications of technology in what seems like disparate fields, because as we all know, everything is physics.

16 Comments
2024/03/17
09:25 UTC

26

Hexagonal light patterns through two planes of hexagonal-packed circular holes.

So l am standing at a distance of 5-6 meters away from two metal sheets of hexagonal-packed circular holes. The sheets are separated at a distance of ~1.5 meters, and the circles are a little less than 1 cm in diameter and are packed as shown in the picture (although the separation distance of the circles is just a little greater in my situation).

Why do I see these big, hexagonal light patterns?

Circular hole configuration.

Figure describing the situation.

4 Comments
2024/03/16
21:04 UTC

8

Textbooks & Resources - Weekly Discussion Thread - March 15, 2024

This is a thread dedicated to collating and collecting all of the great recommendations for textbooks, online lecture series, documentaries and other resources that are frequently made/requested on /r/Physics.

If you're in need of something to supplement your understanding, please feel welcome to ask in the comments.

Similarly, if you know of some amazing resource you would like to share, you're welcome to post it in the comments.

5 Comments
2024/03/15
13:00 UTC

5,455

I guess the journal is using "AI" for its editor as well

213 Comments
2024/03/15
12:32 UTC

104

How much physics do I need to know to understand the standard model?

I want to understand what each of the particles do and how they fit into that massive equation. As for my knowledge base right now, I'm working through the E&M portion of resnick and halliday at the moment and I'm in a multivariable calc course through my school(finished everything except vector calculus rn) and I'm taking a virtual differential equation course(I'm not learning much from it to be honest, I didn't realize it was asynchronous). What textbook/course should I start going through after I finish resnick and halliday? If anyone could provide a list of all the books/topics I would need that would be greatly appreciated.

87 Comments
2024/03/15
01:53 UTC

78

How to recapture the love of physics?

I'm an undergrad majoring in physics and I wanted to know if anyone here's ever fallen out of love with physics and if so, how did you revive it?

When I was in high school I found physics to be the most difficult class at first but quickly (and through a lot of hard work) found it rewarding and it became my favorite. When the time came to go to university there wasn't anything else I knew I'd rather study and jumped into a physics program at a top university.

But through the past few years my experience has been less than stellar. My university's physics department isn't really teaching-focused and my learning experience has been abominable. I don't want to get into too much detail but a lot of my courses have been disorganized and, as one alumni I talked to put it, unnecessarily difficult for the sake of being difficult.

While I managed to pick up my grades, I never really was able to rekindle the excitement I had for physics when I started my undergrad. Now that I'm looking towards grad school I'm afraid I have no desire to continue on in this field. All I can wonder is what happened?

Has anyone here ever experienced something similar in their academic journey? Were you ever able to recapture the love you had for the subject when you first began? If so, how did you do it?

23 Comments
2024/03/15
00:21 UTC

9

Careers/Education Questions - Weekly Discussion Thread - March 14, 2024

This is a dedicated thread for you to seek and provide advice concerning education and careers in physics.

If you need to make an important decision regarding your future, or want to know what your options are, please feel welcome to post a comment below.

A few years ago we held a graduate student panel, where many recently accepted grad students answered questions about the application process. That thread is here, and has a lot of great information in it.

Helpful subreddits: /r/PhysicsStudents, /r/GradSchool, /r/AskAcademia, /r/Jobs, /r/CareerGuidance

6 Comments
2024/03/14
13:00 UTC

891

I accidentally referred to an electron as a “negatron” in my undergrad capstone project paper and I still think about it.

I was in the flow and referred to positron-electron annihilation as a positron-negatron annihilation in the title and and I never noticed it.

120 Comments
2024/03/14
12:21 UTC

57

Bicycle with locked steering

Hi hi, i have a question about the physics of bicycles, maybe someone smarter than me can help me out. I made a bet at work, basically, a colleague said that when the steering is locked in both directions (so the wheels stay perfectly parallel) you are still able to ride the bicycle around corners with very large radii. All he needs to do to steer is shift his weight precisely enough so he wont fall over. I disagree with him, as he can't countersteer to realign the point of contact with the road and the center of gravity, so he will fall. Does anyone have an explanation as to why i'm wrong or why he is wrong?

35 Comments
2024/03/14
09:01 UTC

12

How can i access a supplementary data on ScienceDirect/Elsevier

Is it hidden or i have to subscribe to the journal to see it. I genuinely tried everything to access the supplementary data of this paper https://doi.org/10.1016/j.apradiso.2016.04.005 i checked all journals where the paper shows up, articles and blogs.

At the end of the paper they state in the Appendix " Supplementary data associated with this article can be found in the online version at" I don't know where or how, i just can't find it. the authores btw haven't responded to my emails in like a ~month.

thank you all for the help in advance,

8 Comments
2024/03/13
12:59 UTC

30

NSF Travel Grant for Gravitational Physics for Young Researchers - Marcel Grossman conference

The National Science Foundation has funded a grant which contains sufficient funds to support a small number of young American gravitational physics researchers (American citizens or green card holders) who wish to attend the 17th Marcel Grossman conference which will be held in Pescara, Italy during July 7-12, 2024. This conference, following the established pattern of the previous Marcel Grossman meetings, will focus on a very wide area of topics in gravitational physics and astrophysics and cosmology. Outstanding researchers in these areas of research are expected to speak at the conference.

Further information regarding the 17th Marcel Grossman conference can be obtained indico.icranet.org/event/8/).

Young American researchers who are interested in applying for funds to travel to this conference are invited to apply for support by the NSF grant by April 30.

Your application should include the following information:

  • Your Name
  • The institution and year of your PhD:
  • Your current institution
  • A very short description of your research interest
  • A list of one or two of your publications
  • A paragraph of support from your Ph.D. or postdoc advisor by separate email

Please send your application for this travel support by April 30 to Jim Isenberg Isenberg@uoregon.edu.

Please note that those researchers who have their own NSF grant support are not eligible for this travel support.

0 Comments
2024/03/13
12:23 UTC

106

According to Charles "Chip" T. Sebens, a researcher who studies the philosophy of physics, electrons and other subatomic articles do actually spin. Thoughts?

I am a chemical engineering student, so unfortunatley quantum mechanics is definitely not something I grasp that well. However, I am currently doing a thesis involving NMR, which is dependent on the spin of nuclei.

When trying to understand the phenomenon, it ultimately seems like the major consensus is that particles such as electrons are "point particles" that have intrinsic angular momentum. In other words, they appear to have angular momentum while not actually spinning themselves.

However, I came across this seemingly popular-science article suggesting otherwise: https://www.caltech.edu/about/news/do-electrons-spin

The following paragraph is directly taken from the article above,

"In several studies, including a recent paper in the journal Synthese, Sebens outlines why he thinks an electron is not a point-size particle that merely acts like it is spinning but rather is a spread-out blob of charge that truly rotates. Going back to the ice skater analogy, the electron is instead like a skater with their arms spread outward."

The recent paper: https://doi.org/10.1007/s11229-022-03844-2

Charles T. Sebens appears to have a master's degree in physics and philosophy of physics, which I interpret as him having academic merit. However, since this topic is waaaay out of my field of expertise, I was curious about the opinions of those that have a more nuanced understanding of particle physics regarding Sebens' proposition.

77 Comments
2024/03/12
14:34 UTC

271

Amazing YouTube lectures on general relativity

I recently found this beautiful set of lectures on general relativity by the International Winter school on Gravity and Light from 2015 and wanted to share it. Here is the link to the playlist https://youtube.com/playlist?list=PLFeEvEPtX_0S6vxxiiNPrJbLu9aK1UVC_&si=xw6Ow0P8wU5AIT62

The lecturer has a very clear style and is highlighting important concepts or points where misconceptions arise frequently, which I find really nice. I hope some of you will also enjoy these lectures.

20 Comments
2024/03/12
13:06 UTC

6

Physics Questions - Weekly Discussion Thread - March 12, 2024

This thread is a dedicated thread for you to ask and answer questions about concepts in physics.

Homework problems or specific calculations may be removed by the moderators. We ask that you post these in /r/AskPhysics or /r/HomeworkHelp instead.

If you find your question isn't answered here, or cannot wait for the next thread, please also try /r/AskScience and /r/AskPhysics.

19 Comments
2024/03/12
13:00 UTC

209

What big thing(s) are top physicists racing to figure out currently ?

82 Comments
2024/03/12
03:10 UTC

79

what’s something you have developed (personally) during your time as a physics student, apart from physics itself?

69 Comments
2024/03/12
02:01 UTC

34

Physics Journals

What journals do physicists normally turn to to stay up to date on current research/publications? As a fledgling physics major, I know I won't be able to understand most of it, but I'd like to start looking at the same thing physicists are.

19 Comments
2024/03/11
21:40 UTC

31

Creating Ultra Realistic Physics Simulations - How to Render

Kind of a noob still. But I am insanely curious as to how people like this:

https://www.youtube.com/watch?v=yX84nGi-V7E

are able to create so crisp fluid simulations.

From what I understand they must implement their own physics / modify an exisiting physics engine to get the physics of this to work. But what program are they using to render the scenes? It must be a flexible program to allow for the modification of the physics engine?

Does anyone have any idea what program they are using?

11 Comments
2024/03/11
17:15 UTC

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