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Posted by dmitrybrant 10 hours ago

Show HN: What if the speed of light was 5 km/h?(rivendell.dmitrybrant.com)
I've always wanted to make a visualization where the speed of light was scaled down to human speeds, so that we could intuit relativistic effects with everyday objects. Here is the first version of it!
377 points | 157 commentspage 4
pfdietz 5 hours ago|
The Schwarzschild radius is proportional to c^-2, so this would mean the Schwarzschild radius of the Earth would be about 400 billion km, and the Earth would be a black hole.
mark_something 3 hours ago|
If you're allowed to change the speed of light, you can also change the gravitational constant G to compensate since the Schwarzschild radius is r = 2GM/c^2, where M is the mass of the object.
zkmon 4 hours ago||
Light doesn't have a "speed" as in the usual meaning of the word "speed". Talking about speed requires defining spatial distances and time durations, which are in turn defined or created by the phenomenon of light.

Light doesn't "travel". It's just an exchange of entangled photons creating the concept of time duration and distance.

adamtulinius 4 hours ago|
So how do you explain that light can be slowed down?
zkmon 3 hours ago||
The same way as we talk about it's speed and travel etc - using higher level human perceptions.
nomilk 6 hours ago||
Feels like W goes back (instead of forwards like in an FPS), and S goes forward. Is that intended or just my keyboard being weird?

EDIT: ah, by setting 'Speed of light' parameter to 40km/hr I find it a bit more intuitive

bouncycastle 4 hours ago||
I think it is an illusion because as you approach the speed of light everything in your wide view contracts to the front of where you are going, so it would seem like you are moving back. Stop, and you now appear closer. It's probably why you do not see this effect on sci fi films, instead they show the ship moving forward by streaking the stars showing through the window, which is more intuitive for our brains to understand.
samplatt 6 hours ago|||
You're not controlling an FPS character walking, you're controlling the 'throttle' of how fast you're moving fwd or backward. Holding it down increases speed.

Forward means light is hitting your eyes faster, making it look like the distance the light had to cross is condensed, meaning it looks further away.

Moving backwards slights the light hitting your eyes, to the point where you're moving away from the light, so everything goes black.

iceman_w 6 hours ago||
What you are observing is relativistic aberration. W does make your velocity increase in the forward direction.
buttercraft 7 hours ago||
This only works on a desktop? Is there any way to interact with it on a phone?
dragonfax 9 hours ago||
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.
Kranar 9 hours ago||
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 falls apart the moment you subject it to even the most basic scrutiny. For one... it doesn't make sense to talk about a speed through time since speed is literally a measure of change with respect to time, so a change in time with respect to time doesn't make any sense.

But as a slogan, it captures the idea that motion through space and the rate of your own clock are tightly linked together.

pixl97 9 hours ago||
>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.

Kranar 8 hours ago|||
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.

bilekas 8 hours ago|||
Are you trying to tell me time is relative?
qurren 8 hours ago||
As understood by general relativity, it actually is. There is no absolute time.

You can say the age of the universe is 14 billion years, but that's in our reference frame.

In another reference frame it may be a different number.

bilekas 8 hours ago||
I'm being flippant
eggn00dles 9 hours ago||
well the meter and the kilogram themselves are either completely or partially defined by the speed of light. its a fundamental constant that a large portion of nature depends on, so i doubt such surgical changes could be realized.
fennec-posix 6 hours ago||
This is what it's like with my new glasses
swiftcoder 5 hours ago||
For some reason I get a black screen in Safari. Renders ok in Brave on the same MacBook Pro.
baalimago 5 hours ago||
So it's without collisions, I take it?

I got confused by the premise. To the fully blind person, the speed of light does not matter. He'll hit the object 5 meters away from him regardless if he sees it or not (as will everyone else, but it'll look weird).

throwaway893257 2 hours ago||
This looks oddly similar to a psychedelic trip.
wging 9 hours ago|
See also https://gamelab.mit.edu/games/a-slower-speed-of-light/, a 2012 game that did the same thing
vunderba 9 hours ago|
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.

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