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.

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.)

The fact that this gif has a brief pause between the "ex" and the "explain" really irks me

The simplest explanation I know: Nothing can travel faster than the speed of light. If you ever end up with something that makes the speed of light change, it's actually time that changes.

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.

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?

You're already traveling at the speed of light minus 1m/s relative to a reference frame that's traveling away from you at that speed.

No. Ever heard of the doppler effect?

Light behaves like a wave. But instead of hearing sound in a higher/slower pitch relative to the source, you'd be seeing a different color.

If you're going at the speed of light minus 1 m/s and you turn on a flashlight, the beam emitted by the flashlight will be travelling at the speed of light, according to your measurements. Time passes slower the faster you travel.

Thing go slow - > speed act normal, speed add up between POV's, speed make sense AF

Thing light fast like - > speed act fucky wucky, speed don't add up at all between POV's, speed so fast make time fucky wucky too

I suggest watching these videos from Float Head Physics. They're just some of the clearest and most intuitive explanations of relativity I've seen, and any other explanation I give here would just be me attempting to paraphrase him.

https://www.youtube.com/watch?v=Zkv8sW6y3sY https://www.youtube.com/watch?v=Vitf8YaVXhc

He has a whole playlist on special relativity which is really insightful if you want an even deeper dive, as well as playlists on other things like general relativity and quantum mechanics, all of which are based on building intuition instead of starting with complicated math equations.

For what it's worth, there's a damn good reason that Einstein's name is associated with being super smart.

you and two friends, Al and Be, are outside at night time. Al has a flashlight and flashes it at you and Be. Be is 20 feet away from Al, and you're 20 feet behind Be.

      20ft         20ft
Al..........Be...........you
       r1          r2

The photons from the light Al has hits Be first, so he sees it first. it took .03 seconds(r1) to reach Be.

After that, the photons hit you and you can see it. it took .03 seconds(r2) to reach you from Be.

They were both .03 seconds because you are equally apart and the speed of light is finite.

so, how long did it take the light to reach you from AI?

And that is what is meant by time dilation, and why Matthew Mcconaughey was younger than his grandkids. His balls took longer to bounce......

Great explanation, well done!

In relativity both the planet and the ship see the other as moving slow. Not one fast the other slow.

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.

Doppler who?

So, even if I run very fast, I still don't reach in time for the target people.
Welp, I just have to start early.

If they have no mass, how do they push solar sails?

Thanks for fucking up my mind so I can't get anything done at work for the rest of the day lol

So it's woven with space?

I remember learning that if a quasar is spinning fast enough, then the radio waves inside are theoretically traveling faster than light. Which means that some of the star's mass is actually experiencing time in reverse, until they breach the corona.

The same thing does happen with light, in that your simple first example does need to consider relativity if you want to be exceptionally precise. It's not correct to suggest these two scenarios are fundamentally different, where only one needs lorenz corrections. In truth, both scenarios do, its just that the correction is so insignificantly small for the first example that it can be left out without any significant change in the answer.