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Show HN: What if the speed of light was 5 km/h?

rivendell.dmitrybrant.com

11–20 of 218 posts

Re: Show HN: What if the speed of light was 5 km/h?

#11
Velocity raptor is a free game that accurately simulates the effects of special relativity. It slows down the speed of light to 3m/s and you solve puzzles as a cute dinosaur. https://www.testtubegames.com/velocityraptor.html

There is also a helpful FAQ which explains all the strange things happening, such as length contraction, time dilation, and color shifting: https://testtubegames.com/srel101.html

My favorite levels are #18 (which demonstrates time dilation), #26 (which demonstrates space warping), and #42 (which demonstrates retarded time https://en.wikipedia.org/wiki/Retarded_time ). All the levels are unlocked and you can skip to any level.

Re: Show HN: What if the speed of light was 5 km/h?

#12
post #5

See also https://gamelab.mit.edu/games/a-slower-speed-of-light/ , a 2012 game that did the same thing

There's a great demo video of it as well.

https://youtu.be/uu7jA8EHi_0

Some of the details in the paper are super cool. Since the game pulls "c" down to near walking speed, you receive photons at different rates depending on their direction relative to your motion (relativistic aberration / searchlight effect) resulting in neat visual shifts.

I don't usually download games, but I might have to make an exception just to try it out.

Re: Show HN: What if the speed of light was 5 km/h?

#13
post #7

Well I'm not a physicist, but we all travel through time at the speed of light. With a much smaller speed of light, I think relativistic speeds would be much easier to achieve. I.e. you could age noticeably differently than your family on a solo car drive to get groceries.

The more accurate statement is that all objects have the same speed in spacetime . Time is just one dimension of spacetime and objects do not all travel along that dimension with the same speed. For example, an object travelling through space at close to the speed of light will have a speed along the time dimension close to zero. Having said that... this is mostly a slogan and makes for good Youtube videos, but it fa…

>it doesn't make sense to talk about a speed through time

Only if you're talking about other people's clocks and not your own. Your own clock is one second per second, but someone else's may be slower or faster relative.

Re: Show HN: What if the speed of light was 5 km/h?

#16
post #13
post #7

Earlier quoted context omitted.

The more accurate statement is that all objects have the same speed in spacetime . Time is just one dimension of spacetime and objects do not all travel along that dimension with the same speed. For example, an object travelling through space at close to the speed of light will have a speed along the time dimension close to zero. Having said that... this is mostly a slogan and makes for good Youtube videos, but it fa…

>it doesn't make sense to talk about a speed through time Only if you're talking about other people's clocks and not your own. Your own clock is one second per second, but someone else's may be slower or faster relative.

Once again, just subject your slogan to some basic scrutiny. Your own clock is one second per second, which is a pure number, 1... that's not a speed.

So then you say take someone else's clock and compare it to your own clock, but that is still just a pure number. A speed is not a number, it has units like meters per second. A ratio of two clocks has no units at all, the units cancel. Whatever number you get, 3 or 9, it's just a factor by which two clocks disagree. You can absolutely interpret this ratio as a rate, but that doesn't make it a speed.

And a speed is exactly what the slogan needs, because the diagram/geometry it's using involves a right angled triangle where on one side of the triangle is your speed through space, and on the other side of the triangle is your speed through time, and the hypotenuse of the triangle is fixed at c (since every object travels through spacetime at this fixed speed).

For that to mean anything both sides have to be the same kind of quantity. You can't put meters per second on one side and a bare number on the other and call it a triangle. Nor can you patch it by multiplying the ratio by c to give it units, because the thing you get then grows as you speed up instead of shrinking. Either it has the right units and the wrong behavior, or the right behavior and no units at all. There's no version of this geometry that produces a consistent picture.

Re: Show HN: What if the speed of light was 5 km/h?

#19
post #13
post #7

Earlier quoted context omitted.

The more accurate statement is that all objects have the same speed in spacetime . Time is just one dimension of spacetime and objects do not all travel along that dimension with the same speed. For example, an object travelling through space at close to the speed of light will have a speed along the time dimension close to zero. Having said that... this is mostly a slogan and makes for good Youtube videos, but it fa…

>it doesn't make sense to talk about a speed through time Only if you're talking about other people's clocks and not your own. Your own clock is one second per second, but someone else's may be slower or faster relative.

Are you trying to tell me time is relative?

Re: Show HN: What if the speed of light was 5 km/h?

#20

In the Three Body Problem Trilogy by Liu Cixin some of the more advanced civilisations have the ability to change the speed of light locally with very interesting consequences for the that local space

Pedantic note: The speed of light in glass, optical fiber and water is different from vacuum (much lower). On a certain scale, humanity also knows how to locally alter the speed of light though not to this extent.
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