I'm a 25 year veteran of teaching physics. I've taught IBDP for 13 of those years. I'm now teaching a unit on cosmology and I'm explaining redshift of galaxies. I UNDERSTAND REDSHIFT, this isn't the issue.

The question is this: since the light is redshifted, it has lower frequency. A photon would then have less energy according to E = hf. Where does the energy go?

I've never been asked this question and I can't seem to answer it to the kid's satisfaction. I've been explaining that it's redshifted because the space itself is expanding, and so the wave has to expand within it. But that's not answering his question to his mind.

Can I get some help with this?

EDIT: I'd like to thank everyone that responded especially those who are just as confused as I was! I can accept that because the space-time is expanding, the conservation of E does not apply because time is not invariant. Now, whether or not I can get the student to accept this...well, that's another can of worms!

SINCERELY appreciate all the help! Thanx to all!

Maybe this is an unpopular opinion, feel free to leave a comment as to why you disagree if that's the case...

But in my experience at university, those that spent their entire high school career trying to get ahead, were maybe a month ahead of the rest of us.

I'm not saying "don't learn outside of the classroom", because all people with a passion for physics will be drawn towards it, and that's amazing!! But there's a big difference between that and spending hours on end trying to understand math that you're not ready for. The curriculum does a fair job at giving you the knowledge you'll need for university, so don't worry too much.

Spend your time in high school enjoying life, making friends, relaxing, and exploring your interests. If you spend all your time on physics, you will be missing out on good times, and you will also be less well-rounded in the future.

Once again, feel free to leave a comment if you disagree, this is just my opinion.

Edit: wow I'm glad there's so much input. I highly encourage any young high school students to read the comments and see both sides of the debate. If you have any questions for me, my DMs are open as well!

I just don’t completely understand the way the orbit works. Light takes about 8 minutes to get from the sun to the Earth. I can’t find a reason why the Earth doesn’t orbit where the sun was 8 minutes ago.

I might be a little stupid for asking the question, but I’m just trying to learn more as a high school freshman.

My father passed away. He was very interested in fundamental physics and spent 35 years working independently on ideas related to dark matter/ alternatives to it. I now have his laptop with extensive notes, equations, and drafts. I am not claiming the work is correct or groundbreaking, and I don’t have the expertise to evaluate it myself. I’m trying to figure out the most responsible way to handle this material: How can I tell whether this is personal exploration vs. something resembling formal research? Is there a way to have someone qualified look at it without wasting people’s time or violating academic norms? Are there archivists, historians of science, or academic channels that make sense for something like this? My main goal is preservation and respect for his work, not self publication or validation.

Any advice on next steps would be appreciated. Thank you

EDIT/UPDATE: First thank you to everyone who has taken the time to comment thoughtfully. I genuinely appreciate the range of perspectives shared here. I’ve also received an extraordinary number of DMs expressing interest and a willingness to help and I’m very grateful for that. I’m doing my best to respond to people as I’m able. One small but important request: please don’t reach out asking for snippets of my father’s work purely for curiosity or entertainment. Especially if you’re not active in the field. I’m trying to be respectful of everyone’s time (including my own) and to handle what he left behind with care and intention. Thank you again -C

The Hiroshima bomb was 15 kt. Is there an equivalent kt number for Chernobyl for the sake of comparison? One cannot plant crops in Chernobyl; is it the same in downtown Hiroshima? I think you can’t stay in Chernobyl for extended periods; is it the same in Hiroshima?

I get the sense that Hiroshima is today a thriving city. It has a population of 1.2m and a GDP of $61b. I don’t understand how, vis-a-vis Chernobyl.

To be clear, I am not asking why there is a maximum speed, I am asking why the maximum speed is 299,792,458 m/s. I am also not asking "what is special about the number 299,792,458?", I know it's the number of meters (a human construct) light travels in a vacuum in one second (another human construct).

I am asking why the speed of light is what it is, instead of something faster or slower. Why isn't the speed of light five meters per second, or one billion? What laws of the universe led to the maximum speed being 299,792,458 m/s instead of some other speed?

It's fine if the answer is "as a species we don't know." or "we don't know for sure, but here are some guesses."

My daughter likes asking difficult questions (she knows its a good way to get dad's full attention). She have previously asked "HOW does gravity work?" and I have explained about larger masses attracting smaller, curvature of spacetime, etc. But she could sense that my arguments became cyclical explaining gravity with gravity, so she follows up with "WHY does gravity exist?". I answered: "That is a dame good question. This have been the biggest question in physics the last 100 years, and nobody knows the answer to it." Now she keeps coming back to question and I need something more to tell her or show her. Do you have some suggestions?

As the title says, I have a friend who vehemently believes that force of gravity unironically does not exist. He listened some random person on a podcast say how we are merely being heavier than air which causes us to be pulled downwards. How would I disprove this?

Assuming air resistance is negligible and that the ant won’t burn up before it reaches you.

I applied to and got accepted into a highly competitive summer class with 20 people, but I'm the only girl. The teacher doesn't seem to like me and is noticeably ruder to me compared to the male students. The other students flat out ignore me, and my ideas aren't taken into account, even when I end up being right. It's been a month, and I'm feeling depressed and inadequate. I'm not an exceptional student, but I'm not dumb either, yet I'm being treated like I don't belong there. Does anyone have any advice on how to handle this situation? I’m really starting to hate physics.

Edit: thank you so much for all the support. It is really motivating

Now I don't really know what he did to earn his degree, but when we try to argue with him about it he gets real mad, showing us some equations and proofs that we don't understand and then smirks. We are literally high school students, i don't know why he feels like he's winning anything... Can you please suggest a way to convince him it's not actually flat?

Assume the bomb is trapped in a steel box, it is completely sealed. How many feet thick would the steel need to be to contain the entire explosion?

the idea that energy cannot be created is hard to comprehend when you think about the fact that the universe has a beginning. so how did energy get created if it cannot be created? if it truly was created by the big bang, then wouldn't it be possible to create more matter? tell me your thoughts

I hope this is the correct thread to ask this... We all know computers are designed with 2 states (on/off, high/low, whatever), but why couldn't you make them with 3 states (negative, neutral, positive)? Is there something at the atomic/physical level that doesn't allow a computer to compute outside of a binary state?

This question has been bothering me ever since I learned about relativity, because neither answer seems correct. If it takes 4 years from the perspective of someone on earth, that means it must take less than 4 years for me, meaning that I would be moving ftl from my perspective. On the other hand, if it takes 4 years for me, that means it must take longer for people on earth, which implies that accelerating something faster actually makes it go slower from your perspective.

I don't wanna give up on physics, I wanted this my whole life, I'm now 19 and I lost that passion I had. To be honest, I don't study that much but, I used not to have to study in high school, I just found everything easy in both math and physics because I liked it. I don't have this ability now and it makes me question whether I still like physics or not and whether my brain is fast enough. Did you ever have a similar experience?

Edit: I just wanna say a big thank you to this community for helping and supporting a stranger like me. You made me understand that motivation isn't something that comes out of the blue, as someone said here, you have to get into a positive feedback loop and something like that comes only with hard work and sacrifices. Now that I know this I have no excuses regarding my intelligence, this is not the problem. I also play the guitar, I thought that this is the only thing left to enjoy because I was also starting to get bored of game development (another hobby of mine). Turns out I got unmotivated to play the guitar as well today. Wanna know why? I have learned all the basic stuff, I learn on my own and I feel lost, I feel like I make no progress and that makes me unmotivated. However, this time I know how to deal with it, just like physics and game development, I will keep practising and I won't give up. I will also try to procrastinate less and focus more on the things I love so that I don't abandon them and most importantly, they don't abandon me. A BIG THANK YOU to everyone who made me understand this. Keep evolving!

I've been watching her channel for a few years and noticed a trend that she is getting more and more vocal about her dissatisfaction with academia. While she mostly talks about particle or fundamental physics, sometimes it comes across as blanket disdain for all of science. Her messaging has become quite radical now stating "science is failing" and we should "defund academia" and "most science paid for by taxes is bullshit".

I'm a chemist by training and now a materials science PhD working on photovoltaics. So while I'm not a physicst, I have experience in academia and try to keep up to date with many fields. There are of course ample problems as anyone can plainly see, the paper mills, the sociopaths, the poor progression / reward. But, I truly fail to see how "science is failing". People are doing incredible work across so many fields and even my particular field has been very exciting the last decade.

I understand the stagnation in fundamental understanding on the nature of the universe, but her messaging seems unfair to me.

What are your thoughts?

Saw it on big bang theory

I am on a quest to find verified physics facts that defy belief, challenge our perception of the universe, and are backed through rigorous scientific experimentation.

Which one fact, whether it be time dilation, quantum entanglement, or something even more mind-boggling, changed your understanding of the universe?

I want to start with quantum mechanics, but I only have a surface information Do you recommend this book? If not please recommend one for me.

Stephen Wolfram's advice to students is shocking: don't major in computer science.

He thinks it's a huge mistake.

CS departments have become trade schools for low-level programming. You're learning the modern equivalent of Assembly Language—skills that will be totally automated away.

The real intellectual frontier isn't learning to code, it's learning to think computationally.

Wolfram's advice: major in "Computational X".

Take any field—biology, archaeology, linguistics—and apply the computational paradigm to it. That's where all the low-hanging fruit and genuinely new discoveries are.

If you just want a degree that exports well to any field, his pick is even more surprising: Physics.

Why? Because it teaches a general, quantitative methodology for modeling the world. It’s a framework for thinking, not a temporary skill.

📽️ Full interview here: link.

What do you think? Is he right — is CS already outdated? Should more students be learning to think computationally instead of just learning to code?

I see a lot of questions that have been downvoted but have a dozen or more very well thought out answers that phrase their explanation at an appropriate level. First off, thank you to all the people who put in the effort to answer. Secondly, we are here to improve scientific literacy, correct misconceptions, and help people to better understand physics. Don't downvote an honest question just because the person asking it has fallen into the same common traps that people before them did. If those questions annoy you, just ignore them and move on.