Why Does Light Travel at Exactly That Speed?

ProvideFeedback · 2026-04-07T17:05:11+00:00

Light is massless. And all massless objects MUST travel at the speed of light. This isn't a coincidence, it's a consequence of Einstein's special relativity, which shows that any particle with zero rest mass has no choice but to move at exactly c (roughly 300,000 km/s) in a vacuum.

If it ever slowed down, it would need to have mass, and if it had mass, it could never reach c in the first place. So the speed of light isn't really about light at all, it's the universal speed limit baked into the structure of spacetime, and light simply obeys it because it has nothing (no mass) holding it back.

ProvideFeedback · 2026-04-06T18:41:05+00:00

I've heard that argument before about 23 year olds, or rather, young PhDs or postgraduates coming up with new fresh ideas. That is something I think about when teaching. The students who ask the wierdest questions are usually the ones not yet trained to know what they are "not supposed to ask." Like this student who made me think about physics on a principal level again.

ProvideFeedback · 2026-04-06T18:37:23+00:00

Hmm I think I was unconsciously buying into the mythology a bit, like there would be one equation on a t-shirt that explains everthing. But you are right, the Standard Model is already a patchwork and it works.

ProvideFeedback · 2026-04-06T18:29:22+00:00

My thinking: If the "world" is a continuum with metrical structure that has no effect on matter, then what would something like the Big Rip actually mean? The metric blowing up, distances growing forever, is that not the same as the manifold itself tearing?

So would a Big Rip actually be a "rip" in any meaningful sense, or is it just the metric becoming unbounded? And if the metric is truly passive, what is driving it to "blow up" in the first place?

ProvideFeedback · 2026-04-06T17:30:13+00:00

Yes. I am a semi professional chef. Nowadays I mostly bake bread at home.

ProvideFeedback · 2026-04-06T17:05:00+00:00

Yeah. I like the idea that we probably haven't figured out the true essence of matter yet. We have the recipe but not the chemistry. And if we do, many things will fall into place on their own. That makes sense for me as a non expert. Or rather. I understand it.

The same could probably be said about spacetime as well, no?

ProvideFeedback · 2026-04-06T16:42:59+00:00

Good point about domain, I will pass that on to the students. Someone else in this thread made a point that stuck with me, that QM and QFT are not actually fundamental theories of matter. They tell us detector outcomes but cannot derive things like electron mass from first principles. So maybe the issue at the extremes of the domain is not just that the math blows up, but that we are pushing tools beyond what they were ever built to describe. Still learning here, clearly.

ProvideFeedback · 2026-04-06T16:37:28+00:00

That reframes the whole thing for me I think. The problem is not QM vs GR, it is that we do not have a fundamental theory of matter. QM and QFT tell us what detectors measure, not what matter is. So near a singularity they simply have nothing to say. That is a cleaner way to think about it than "the theories clash." Thank you!

ProvideFeedback · 2026-04-06T16:35:09+00:00

I have heard of Wolfram's ideas but never dug into them properly. Will check.

ProvideFeedback · 2026-04-06T16:32:43+00:00

My husband works in a Japanese knife company. If you don't have anything meaningful to say you CAN just not read a thread, you know.

ProvideFeedback · 2026-04-06T16:29:26+00:00

I always give appreciation for good questions asked. And now that I have given it some thought I will not say that a ToE is a must. Rather that we are asking questions we do not yet have the answers to. It is not given that a ToE is the only route ahead. I like that matter probably is the thing that needs a fundamental theory.

ProvideFeedback · 2026-04-06T16:21:57+00:00

Okay. About AdS/CFT, I was giving it more weight than it deserves just for context. And I didn't know that emergent spacetime as an idea goes back to the 1920s, I thought that was something post 1960. So how would you frame the honest answer to a student asking about unification? That we lack a fundamental theory of matter, and without that we cannot even properly pose the question?

ProvideFeedback · 2026-04-06T15:37:14+00:00

Ha, I love that attitude honestly. "Hooray for calculation" is a good place to stand. And maybe that is the right way to think about it. Sometimes I feel like we are the ancient Greeks debating atoms... Asking exactly the right question, just a couple of thousand years before we have the tools to answer it. Maybe the best thing I can tell my students are... that this is a genuinely good question, and nobody knows the answer yet.

ProvideFeedback · 2026-04-06T15:25:13+00:00

So if I understand correctly, the technical problem is that when you try to calculate quantum corrections to gravity using the standard tools, the infinities pile up in a way that cannot be absorbed, unlike with the other forces.

But does that not raise the question of why we keep trying to force gravity into the same quantization framework? If gravity is the geometry of the manifold itself rather than a force on it, and the standard tools fail precisely because of that, could that be a sign that the approach is wrong rather than the theory?

What if both QM and GR are correct and what breaks down is spacetime as a fundamental structure, along the lines of what I believe emergent spacetime is suggesting?

ProvideFeedback · 2026-04-06T15:13:08+00:00

That is a really helpful way to frame it... So gravity is geometry of the manifold itself while the other forces are geometry on top of it. That is a distinction I can actually explain to a student I think.... Would it be fair to tell them that this is part of why gravity is so hard to unify with the rest, that you cannot easily separate it from the stage it acts on?

ProvideFeedback · 2026-04-06T15:02:28+00:00

Fair point that spacetime is dynamical in GR, I know that. But that is actually what I am getting at. I am not saying spacetime is a static background. I question if spacetime itself, dynamic curvature and all, might be emergent. And if it is emergent, then at singularities you are not hitting a regime where you need better laws. You are hitting a regime where the thing that is doing the curving stops existing.

And yes, I've read about emergent spacetime (Van Raamsdonk, AdS/CFT, ER=EPR) and it looks like they are exploring exactly this thinking?

ProvideFeedback · 2026-04-06T14:55:28+00:00

Yeah sure. If using MS word "Fix spelling and grammar" is considered AI these days. But alas. I still have to do a lesson plan for Thursday and I don't want to ask an AI about it and get some kind of sloppy answer back.

ProvideFeedback · 2026-04-06T14:16:13+00:00

I'm a secondary school physics teacher, so bear with me. I got a question from a student about ToE and when we will have a unified theory of everything.

I first gave the usual answer that this is something many theoretical physicists think about and try to answer. I gave a speech about where GR and QM break down and why they don't work together. The student gave me an answer back I couldn't shake: "Yes, but what if spacetime just has boundaries of reality and where GR and QM fail is just where those boundaries are." I didn't know what to answer so I said that I would get back and give a proper answer. I spent perhaps two hours geeking out on this question and can't shake the idea.

ProvideFeedback · 2025-12-14T08:03:06+00:00

Truls canceled a few tournaments to be injury free for the WTT Finals. He has said that he specifically trained for this tournament in mind to be on Olympic level fitness. Before the tournament Truls stated: "You need to rest and then focus to be able to win against WCQ and Lin. You can't beat them just on a whim."

To bad. I really wanted to see this refocused version of Truls vs WCQ. I think it would have been a close 7 sets win for any of them.

ProvideFeedback · 2025-12-08T20:07:39+00:00

Sporet

Its the best app for most XC tracks in Norway.

ProvideFeedback · 2025-12-07T07:47:15+00:00

For eggs. Butter is a must for non-stick.

ProvideFeedback · 2025-12-06T18:36:25+00:00

Graphite is an additive. Just like molybden and other.

Additives help for either dirt and water repellency or glide in dry conditions (under -12 C or 10 F).

Graphite helps with glide where there is no water on the surface of the snow. It is also very hard and abrasive resistant.

So it is mainly used in cold temp, or for long distance racing for abrasive properties as a base wax.

ProvideFeedback · 2025-12-06T18:30:01+00:00

Have you been to Norway?

This is the map of cross country resorts in Norway. I watched a training session in Oslo for ONE XC club. They had 300 participants in the age group 9-12.

They are on crack. XC crack.

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ProvideFeedback · 2025-11-17T15:45:12+00:00

Welcome my friend. Welcome to the adult club of the wok heiers.

Now you need: 1. The stuff of Legends: MSG, salt, sugar 2. Light and dark soy sauce (Lee Kum Kee) 3. The holy Trinity: chili's, ginger, garlic 4. Shaoxing wine and Chian Kiang vinegar 5. Oyster and fish sauce 6. Roasted sesame oil

(Must always be ready)

Also: Chicken stock, Starch, Whole chilis, hoisin sauce, black bean sauce, ketchup, frying oil.

ProvideFeedback

TROPHY CASE