r/PhysicsStudents

Some Confusion about the Light Horizon and the Age of the Universe.

The universe is believed to be approximately 13.7 billion years old. We know this partly because the light horizon is about 13.7 billion light years away from us, meaning that it takes the light from the light horizon about 13.7 billion years to reach us here on Earth.

So in essence, when we see the light horizon we are not seeing it as it is NOW, but as it was 13.7 BILLION YEARS AGO. But, if the universe is 13.7 billion years old, then at the place where we are seeing the light horizon, wouldn't we be seeing the universe as it was in its infancy, basically the singularity before the Big Bang, or perhaps at a fairly short time afterwards?

Also, if we are measuring the distance to the light horizon, and thus (partly) determining the age of the universe, from Earth, does this mean that Earth is at the center of the universe, basically where the pre Big Bang singularity once was (or somewhere close)?

Am I the only one who has stumbled on these little dilemmas (if you can call them that), or is this something that physicists have resolved long ago, and I can go back to my layman's concerns?

Would appreciate some insights on this but I hope you can explain it in layman's terms, have some sympathy for us rubes! Thanks in advance.

For context I'm in my third year of my four year degree. These past three years will account for 30% of my grade, with the remaining 70% being from my final year. I am doing a double major in theoretical physics and experimental physics (30 credits each). Every semester I tell myself I'm going to do better and the same thing always happens. I start studying too late because I was overworked doing assignments, I try to cram at the last minute and end up doing pathetically mediocre. I am currently sitting at a high 2.2 which means that if I want to apply for masters programs to go into after I graduate I won't be able to even if I did perfect in fourth year as they would essentially be looking at my 2nd and 3rd year grades(which range from some high seventies to middling 40's) -note this the UK/European system idk how this converts to the American GPA system.

I view having to take another gap year(as I took one already after a bad start to second year) as essentially academic suicide as I would be out for a year and most likely would also not be able to get any sort of opportunities to do with internships or work experience due to the current job market. It feels like the only thing I can do is just keel over and die as my life is basically over and I don't know what to do.

im a 12th grade passout and planning to do bsc physics in some tier 2 private college and then do master's from iit or isi. I want to know if im doing it right? i wanted to get into RnD of physics initially but quant field caught my eyes

any valuable feedback would be helpful thank you!!

I am a 1st yr Applied Physics student. But I was always into theoretical physics. However, I chose it due to some circumstance.

It's not like i hate the subject but i am not enjoying it either.

So, there is little bit fear inside me if i did wrong choosing it.

What's your view and opinion.

I’m an incoming third year undergraduate at a top ten school for physics in the USA, and for several reasons, my GPA is atrocious. I’m talking 2.9 ish, and I will certainly graduate with below a 3.5. I had very serious extenuating circumstances and took a medical leave for a year after freshman year, but have not done well in my classes since returning due to very poor mental health and feeling demotivated due to how bad my freshman year grades were.

I am currently doing summer research at my home institution in quantum computing, which is going well, and have a decent network here. I feel as though I can improve my GPA by the time I graduate, but obviously only so much can be fixed. It was originally my hope to get a PhD at a similarly ranked school and remain in academia as a professor. I still do not wish to give up on the dream I’ve had since I was 12 because I had two years of me going insane and getting bad grades because of it.

I am trying to leverage my options now. Is it best to transfer to another (almost certainly lower ranked) undergrad institution and start over in order to obtain a better GPA? Or should I opt for a masters before applying for PhDs? I do not think I am ready for or would do well in the process of applying directly for a PhD program after finishing my bachelor’s degree, although that is of course an option too. The main thing is that I wish to start over and I am willing to do whatever it takes (including spending however much money) to accomplish my original goal.

Any advice is appreciated. I hope this post does not come across too stubborn, I am just very frustrated about my apparent lack of promising options.

Hi all. I have done all the physics past papers from 2012 up to 2025. The marks im getting have increased from the 2012 to 2025 paper but I need more to revise.

My exams board is QS (old sqa), im national 5, and I cant find any more papers (mock, predicted.. etc) to do but I want to keeo revising before my exam. What can I do?

Note : I didnt do all these papers in a day or anything lol, its been about a week and a half since I started lol

Hey everyone,

A while ago I posted about building an Obsidian-style math note app with interactive geometry tools. But after talking to more students and researchers, I realized the real problem is much worse: the massive amount of time we waste formatting and re-calculating.

Right now, we are forced to pick an extreme:

1 Speed (Handwriting/iPad): Fast during lectures, but it becomes "dead data"-you can't easily search it, copy code, or use it for a thesis without completely re-typing it.

2 Precision (LaTeX/Mathcad): Looks professional, but it's incredibly slow, hard to learn, and if you change one variable, you have to manually update every equation, table, and chart.

Apparently, STEM students and academics spend up to 40% of their time just fighting layout engines instead of doing actual science.

I want to create a next-gen platform to fix this.

The idea is that in the background it runs typst as the backend, but in practice it won’t require learning a new coding language, because it will be as intuitive as AutoCAD is. And it will have a stable engine to suport visualizatio such as graphs and diagrams and other STEM related stuff.

To help me build this, what is your single biggest bottleneck right now?

View Poll

It is literally what the title says.

I will be appreciated for your trigger or stories that made you quit physics.

I'm confused studying physics because the result of nature, for example gravitational force or Coulomb force, do not make me comfortable. And I feel that the way many physics textbooks explain their contexts have bunch of lack of logic.

Thanks for your comments.

Hey all.

I think one big part that is really holding me back in physics is my understanding of linear algebra. Last spring I had a semester where we followed the math people and were in their linear algebra class. I managed to pass, but I got the lowest passable grade, and most of what little I knew I feel like I have forgotten, and I think it is holding me back significantly.

We are coming up on the summer vacation, and I would like to catch back up with linear algebra and hopefully get a better understanding this time around. For that reason I am looking for recommendations on how best to do this. I have looked around a little and looked through old posts, but there are so many possibilities. Except for calculus classes I haven't taken any extra math as I focused on physics, and my education doesn't allow a lot of free choices. This means I haven't had any analysis or algebra math classes, so I would love to learn linear algebra in a way that isn't too math technical or proof heavy if possible.

Hopefully what I am asking makes sense. I have written what I have found below and would love some more insight and advice from people who are much smarter than me :-)

• Linear Algebra Done Wrong, by Sergei Treil - Don't know much about it, but I have seen it recommended before.
• Linear Algebra Done Right, by Sheldon Axler - I actually own this one because when I was buying other books from someone, they had this really cheap, but I have come to learn that it might be too analytical? And also I think it doesn't have a solution manual?
• Linear Algebra - As an Introduction to Abstract Mathematics, by Lankham, Nachtergaele and Schilling - An online textbook I have seen recommended. Worried it might be too technical and "mathematical" too though.
• A First Course in Linear Algebra, by Robert A. Beezer.
• Linear Algebra and Its Applications, by Gilbert Stang - Apparently there seems to be really divided opinions on this?
• Linear Algebra, by Jim Hefferon - Also an online course/book.
• MIT OCW - 18.06 | Spring 2010.
• MIT OCW - 18.06SC | Fall 2011.

Thank you in advance!

I am in the UK and am in my final year of secondary school. I study Maths, FM, physics, and economics A-levels.
Next year (if I meet my offer) I will be studying maths at the University of Warwick. I really enjoy physics and want to self teach some undergraduate university physics to myself (just in spare time in the summer), but am unsure on where to do this. Does anyone know of good online resources to do this? Or even a list of things to study? I would greatly appreciate any help.

Hello! I am soon to attend graduate school to get my PhD in Physics. I had a successful graduate school application cycle and want to pass on the knowledge I gained through the process. I culminated all of my advice into a GitHub website, linked below.

Check it out, and maybe pass it on to people who might benefit! Additionally, there is a feedback form at the bottom of the page for any changes or additions you might suggest. I want this guide to be as thorough as possible.

https://white3792.github.io/rachels-complete-guide-to-graduate-school-applications/