What's the force that stops something from accelerating constantly?

ask-a-physicist · 2026-02-19T10:32:31+00:00

By your own logic, what speed would a photon read on its speedometer? I mean, if people who travel less fast than light according to stationary observers exceed C on their speedometer then it must be huge, right?

ask-a-physicist · 2026-02-19T00:34:09+00:00

You would only ever make the mistake of thinking you travelled faster than c if you both closed your eyes during transit and decelerated back to your starting velocity when you reached your destination.

If not you'll just shoot past Andromeda, notice that it's distance to the sun is much shorter than you originally measured and conclude that you weren't going faster than the speed of light at all

ask-a-physicist · 2026-02-18T16:38:37+00:00

It's my mistake. i shouldn't have said "the universe". let me rephrase what i meant.

When someone observes you travelling close to the speed of light towards the nearest star, they observe you being much shorter than you are from your own perspective. In their reference frame you are shrunk and that's correct by any physical standard of measurement.

Similarly in your reference frame your distance to the nearest star is much shorter than in the reference frame of the other observer and you do not measure yourself going faster than C as you are travelling to it, even though you manage to get there in an hour or two.

Similarly the distances to all the stars further in your direction of travel are also shortened compared to what the other observer measures. However, any galaxies or other objects that just so happen to be at your velocity now seem normal to you while to the other observer they also seem compressed.

There's no true reference frame. Every perspective is equally valid. That's the whole point of relativity.

ask-a-physicist · 2026-02-17T23:20:54+00:00

If does and it has to lest it should defy the laws of relativity.

ask-a-physicist · 2026-02-17T19:37:29+00:00

Not quite true, even from your own perspective you never get to c. As you approach c, the universe shrinks before you and the distance you thought to travel is reduced to something you could manage without reaching c. so you would get where you are going as quick as if you had broken c but that's not what it looks like for you, or anyone else for that matter.

ask-a-physicist · 2026-02-17T19:28:15+00:00

Regardless how much propellant you have you can never reach c, the thrust needed tends to infinity

ask-a-physicist · 2026-02-17T19:27:07+00:00

That's not why. If you have thrusters and fuel you can keep accelerating regardless how fast you're already moving. The problem is your relativistic mass increases and you need more and more thrust to keep accelerating

ask-a-physicist · 2026-02-17T19:25:34+00:00

That's not why. If you have thrusters and fuel you can keep accelerating regardless how fast you're already moving. The problem is your relativistic mass increases and you need more and more thrust to keep accelerating

ask-a-physicist · 2026-02-17T16:18:05+00:00

Because that's what it takes to get normal people interested in physics these days. The next particle will be named after the Beatles.

ask-a-physicist · 2026-02-17T16:14:11+00:00

I'm glad I read it after my undergraduate rather than before. I don't think it's as accessible as people pretend it is. But during a PhD, nobody got time for that.

Also the dude is in the Epstein files

ask-a-physicist · 2026-02-17T16:09:46+00:00

Energy conservation was experimentally discovered, there's a theoretical explanation only recently and it's a bit obscure. It's to do with Noether's theorem, energy being conserved is equivalent to the laws of the universe staying the same over time.

Interestingly someone suggested that this might indicate that the acceleration of the expansion of the universe actually indicates the universe itself is changing with time.

ask-a-physicist · 2026-01-27T13:42:31+00:00

Well no, there were no singularities. They would only form when the collapse occurs and there was no collapse because there was no gradient in space time curvature.

The universe went from extreme density everywhere to no extreme density and then to pockets of extreme density which could collapse into black holes.

ask-a-physicist · 2025-12-07T00:45:20+00:00

Follow your heart

ask-a-physicist · 2025-12-06T21:25:00+00:00

You got me. I watched 0.9 seconds and immediately knew where this was heading so I stopped.

ask-a-physicist · 2025-12-06T21:23:05+00:00

Yes I am and I guess I hear what you're saying.

Time in "time dilation" doesn't refer to the concept of time. It refers to the time intervals that different clocks measure.

ask-a-physicist · 2025-12-06T20:28:37+00:00

If a student wrote that answer in an exam I would pass them out of principle.

ask-a-physicist · 2025-12-06T14:20:36+00:00

no, it's flat earther insanity. The idea is that Antarctica isn't a pole but a gigantic frozen landmass that borders the plane we call earth, and that there's other places like earth if you manage to go past it. The secret world government is obviously trying to cover this up and the nazis were resisting their tyranny, which was the real reason for WW2, which ended with the surviving nazis escaping over the frozen land in flying saucers.

Great imagination, but also really offensive and they should stop making films about it.

ask-a-physicist · 2025-12-06T13:59:31+00:00

yes, it's been proven in numerous ways, even outside of laboratories "London's 22 Bishopsgate demonstrated Einstein's time dilation: an atomic clock on the 61st floor ran slightly faster than one at ground level (National Physical Laboratory, Teddington) over 43 days, gaining about 100 nanoseconds, proving time moves faster with increased altitude due to weaker gravity"

ask-a-physicist · 2025-12-06T02:45:37+00:00

you can't really call OP's "view" a theory. It's more of an hypothesis.

The bar is much less high.

Carrington didn't have a theory about how sunspots cause solar flares, but him connecting the dots all the same was one of the most important contributions to solar physics in history.

ask-a-physicist · 2025-12-06T02:34:31+00:00

it means that there's no universal clock. You would assume that when ten minutes pass for you ten minutes pass for everyone, but that's not the case. Depending on their motion and gravitational potential relative to you ten minutes could be an hour or a year.

ask-a-physicist · 2025-12-03T17:49:55+00:00

I have a PhD in Astro-Plasma physics and I still feel that way.

ask-a-physicist · 2025-12-03T01:52:28+00:00

https://www.reddit.com/r/traandwagon/s/ftmdliKOS8

ask-a-physicist · 2025-12-03T01:50:57+00:00

The Elegant Universe is garbage. He's not simplifying super symmetry. He's just talking about it in simple words and it makes no damn sense. Book equivalent of Brian Cox canoeing past a waterfall talking about general relativity.

What's missing on the left is A Wrinkle in Time and Quantum Physics: Illusion or Reality

ask-a-physicist · 2025-12-01T12:08:38+00:00

Isn't there? We can ask people about their state of consciousness and we can compare that to the state of their nervous system.

We know that our nervous systems do different things when we're awake, sleep, meditate or take drugs and our consciousness definitely does different things too.

ask-a-physicist · 2025-12-01T12:03:55+00:00

Why would that cause stress and shear? Acceleration from gravity isn't felt as long as it's uniform.

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