The speed of light isn't even really a speed, it's a property of space itself.
this post was submitted on 04 Jun 2026
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But it's also a speed
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A bit late to the party, but I'll try anyway!
So, first, speed is distance over time. Miles per second, kilometers per hour, whatever.
Consider a person rocketing by a planet in a little spaceship at a good fraction of the speed of light. To amuse themselves, they're bouncing a ball between two paddles on opposite walls of their craft. The ball describes a path like:
O--------O
--O----O
-----O
Of course, to a person on a planet they're blasting past, the path looks different - the ship moves a long way between each bounce, so they see:
O----------------------------------O
-------O------------------O
----------------O
The thing is, both of these are correct from each point of view - from each reference frame. For the shipboard person, the ball moves the width of the ship, and for the planetside person, it covers the distance the ship traveled in the bounce (plus some for the width).
Now, swap the ball for a photon, which always moves at the same speed. The distance the photon travels from the two points of view - the two reference frames - is different, so the time component of the photon's measured speed must change as well because the photon's speed remains the same! Each side sees the photon moving at the same speed, despite the difference in distance traversed each pov sees - which means each must also have a different measurement of the time involved!
So, time is compressed on the spaceship relative to the planet - from the ship, the planetside observer is moving very fast, while to the planetside observer, the space pilot is moving in slow motion. The speed of the photon is universal - it's the distance it travels between bounces, and therefore how long it takes to bounce, that differs between their perspectives.
And that is what is meant by time dilation, and why Matthew Mcconaughey was younger than his grandkids. His balls took longer to bounce......
Alright alright alright
I want to know why it works that way. I'm pretty sure we don't actually know why that is a law of nature, just that it is. Some of these things I learned in physics I was frustrated that we can't explain the why. We just kind of know this is what experiments tell us, and the math.
If you mean the relativity part, to my understanding space and time are basically a shared dimension, so the faster something is moving in space the slower it's moving in time. Why it's shared, I have no clue.
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If you were on a train that was travelling at 60 mph and you threw a ball (inside the train) and the ball was travelling at 10 mph (inside the train), then the ball would objectively be travelling at 70 mph. Any observer (outside the train) would be able to understand why it looks like 10 mph inside the train and 70 mph outside the train.
Are you with me?
Okay, so the same thing does not happen with light! If you turn on a flashlight (inside the train), the light would be travelling at 670,616,629 mph regardless of whether the train was stationary or moving. So an observer outside the train would see the light travelling at the same speed as an observer inside the train. Even if the train was some supersonic invention from the future, the light inside the train would still be travelling at 670,616,629 mph - not 670,616,629 mph plus the speed of the train. And both inside and outside the train, observers would see the light as travelling at that speed. That's the big thing to get hold of!
How can this possibly be the case?
The answer is that time itself actually slows down when we are in motion. At low speeds, the effect is negligible, but the closer we get to the speed of light, the more the effect becomes observeable, until, when we are travelling at the speed of light, time stands still. If we were able to go faster than the speed of light, we would be travelling backwards through time.
Thanks for fucking up my mind so I can't get anything done at work for the rest of the day lol
Oh it gets even weirder than that.
One observer can see two events happen simultaneously while another sees them happen at different times.
And EVEN WORSE than that, thanks to length contraction at relativistic speeds, you could have one observer think that a train is contained entirely within a tunnel, but another observer sees the train sticking out both ends of the tunnel at the same time without ever fitting entirely within it.
and/or: One observer objectively masures that object A is longer than object B, while another observer objectively measures that object B is longer than object A.
The two observers are not just hanging out together, of course. They are moving ridiculously fast relative to one another.
The speed of causality is a hell of a drug.
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When sailing boats pushed for speed they ended up hitting an unexpected speed barrier. As you increase velocity the break wave created by the bow of the ship elongates until the length of the ship is at 1 wavelength, then the hull drag prevents further acceleration. For a 50 meter ship it's about 17 knots. You can get much faster lifting the boat from the water as you gain speed with an underwater wing, the current max speed was set 47 years ago at ~276 knots. But that's only because they can remove the hull from the high drag environment and is extremely dangerous to attempt to break. The speed of light is nothing like that because spacetime itself can stretch and squish, I just wanted to talk about boats for a bit.
So you're saying, we need to jump the spaceship out from space/time. With a wing.
I love this because this feels like something the 10th doctor would say to confused daleks while stalling
I'm not even mad because now I get why and how these competition multihull boats basically fly above water while keeping like 1% of the boat in water
Those ones are reaching a new speed limit as well, the cavitation around the hydrofoil starts at a certain speed/angle and stalls the foil, which then abruptly drops the hull back into the water.
I’ve been wondering how long before the equivalent of variable swept wings will be added to the cup boats.
Still very interesting
I don't like being deceived John! Tell me more about boats!
You have two observers, moving directly opposite each other.
Each has a flashlight pointing back at the other.
The speed of the light from those torched is the same for both observers.
(Instead the light would be red-shifted.)
Add a third observer, stationary to one and moving towards the other. As the third observer passes that observer, the speed of light from their flashlight never changes, and it’s the same speed as from the other two. (Instead it would go from being blue shifted to red shifted.)
This adds substantially more questions than it answers.
-Scientists after discovering General Relativity
It's complicated (and don't trust me too much, I'm not qualified), but if you've heard of time dilation and whatnot, if you start traveling at speeds comparable to the speed of light, spacetime distorts in such a way that from your point of view all light coming from any direction travels at the same speed.
This is also why (or one of the reasons) according to science you cannot travel faster than the speed of light, since light would still need to be traveling away from you at the speed of light and you'd need to occupy negative space in that direction, or something like that.
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And remember, a photon of light does not experience time. Time only applies to mass. When a photon is emitted traveling at the speed of light, it is eventually absorbed by something, eglight from the sun hitting your eye. The photon of ligjt, from the photon POV is emitted and absorbed in the same instance.
But some of the photon is absorbed by the material it passes through called spectroscopy. I guess then it’s good it’s also a wave, as per the Light Slot Experiment.
It wasn't a wave when I checked.
😂😂😂
No fair, you changed the outcome by measuring it.
Keep the faith. Don't collapse the wave.
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Ok, firstly I'm not very smart. Secondly I don't understand the meme AND don't understand the explanations in the comments.
Can anyone actually dumb it down so a stupid person like me can understand it?
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Okay, but what if I go the speed of light minus 1m/s and shine a flashlight, can I catch the photons?
No
That's not a physics statement btw. I just think that you, personally, are too slow to be able to do that. Offense intended.
That may seem harsh to the casual reader, but it's 100% true in this case.
It's a 100% in all cases. The light doesn't like you and is trying to get away.
One day we will all be shrouded in the darkness we've created for ourselves.
You can catch the photons just fine without needing to go absurdly fast. Just put your hand in front of the flashlight beam, and you'll catch lots of them.
Physicists hate this one weird trick
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Light ALWAYS travels away from you at the speed of light no matter how fast you and your flashlight are going. Something has to give and that is time. It may look to outside observers, not traveling that fast along with you, that light is going 1 m/s faster than you... but you would also appear to be moving in super slow motion trying to reach out for the beam. The faster you go the slower time moves for you.
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Nope. In your frame of reference, they will still be moving at the speed of light.
I think the answer is that you are only traveling at almost light speed from reference frame of your start position.
The light of the lamp travels at light speed from your own reference speed which to you in a vacuum is 0.
Anyone correct if wrong please?
Correct. Physics gets really, really weird at relativistic speeds. Something to keep in mind is that the speed of light isn’t actually the speed of light itself, but rather the speed of causality - the universe’s hard limit at which any interactions can occur. Even if you are traveling at .99c from a certain reference frame, space time itself warps in such a way that light traveling away from you is still measured at 1c
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I think it's neat that Newton is taught first. As in: gravity is a function of mass. Because that works in so many scenarios.
But then you learn that gravity bends light and that photons have no mass.
So.... Gravity isn't a force, it's more like going downhill... in the dimension of time.
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