Show HN: What if the speed of light was 5 km/h?
7 hours ago (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!
At first sight, this is remarkably more accurate that the "slower speed of light" game from MIT that was made available all those years ago (~2012).
Many issues with the MIT game were discussed here:
https://physics.stackexchange.com/questions/43695/how-realis...
While the thread lists multiple issues, the issue that I found was with modeling temporal aspects of relativistic doppler (I also reported it on the github repo of the "slower speed of light" project, but that doesn't appear to be maintained):
https://github.com/MITGameLab/OpenRelativity/issues/17
In this game, it looks like the temporal component of the Doppler effect is modelled correctly.
Some time ago I had the following shower thought: "the Speed of Light is pretty slow"
How i got there:
The closest major galaxy to the Milky Way is Andromeda, and is 2.5 million! light-years away. And this is the CLOSEST galaxy, the universe is extremely big.
Of course that as you get closer to C, the traveling object will experience time dilation (relative to observer), so the time passed will be less. At 99.999% C, the traveler would take ~11,000 years to arrive to Andromeda.
So again, even at 99.999% C, 11K years seems like a LONG time to reach even the closest galaxy.
My reasoning was: the speed of light is pretty damn slow.
But then I realized: no, it's not the speed of light that is slow, is my frame of reference.
For us humans, 11,000 years seems like A LONG time, but for the universe is not that long.
The universe's age is estimated to be 13.8 billion years. 11,000 years is 0.0000007971 of the age of the universe.
An average human lives 70 years, 0.0000007971 of that lifespan is approximately ~0.4 hours, or 29 minutes, so it's not that bad.
So yeah, frame of reference matters.
Not only that, from light's perspective, it takes no time at all. ;)
> At 99.999% C, the traveler would take ~11,000 years
if we add more 9s, is it possible to reduce that number to within a human lifespan?
Yeah, it is and the math get's really counterintuitive to grasp since humans (at least me) have trouble thinking in exponential terms.
If you accelerate at 1g constantly for 1y you travel 0.5 light years. You do that for 10.5 years and you reach the center of the milky way. You do that for another 4 (~14 total) years and you are in the Andromeda galaxy, and you do that for another 10 years (~24 years total) and you reach what today is considered the edge of the observable universe.
By the time you get there you are basically traveling at a rounding error from C.
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Yes. Time dilation (with respect of the stationary observed) is calculated using the Lorentz factor.
At 99.999% of C, the Lorentz factor is ~223.6.
It grows pretty quickly as you add more 9s to the fraction. Every two additional 9s multiply the Lorentz factor by ~10.
So at 0.99999999999 c, it'd be ~223,607x.
2.5M years / 223,607 is: ~11 years
Of course this is all highly theoretical.
https://en.wikipedia.org/wiki/Lorentz_factor
Proper time asymptotically approaches zero here right?
Yes. If you can manage to get arbitrarily close to the speed of light, the amount of perceived time would get arbitrarily close to zero.
One oddity of Lorentz invariance is that two non-parallel boosts decompose into a boost and spatial rotation.
I've never quite wrapped my head around this and was hoping to get some insight from this simulation. But afaict, I'm not seeing this effect (press W for a bit, the A for a bit and it's not obvious I'm at a different orientation - if I look down at the ground the gridlines are still axial).
I don't know if I'm misinterpreting the math, or the simulation, or maybe the simulation is doing something to 'correct' for this behavior so things are more natural, or something else. Does anyone have any insight?
This is very interesting! Have you posted any simulations based on this? Really cool idea I had not come across before!
Whenever I think about light speed being fast, I imagine myself standing at the edge of the solar system and watching a hypothetical photon travel from the Sun to the Earth and taking 8 minutes. Suddenly it doesn't feel like light is really all that fast except at human scales. 5 km/h would be fascinating though.
The globe here is, in my opinion, the best such visualization because I've personally travelled the distances depicted.
https://www.reddit.com/r/educationalgifs/comments/qq5cw7/coo...
The speed of light is unbelievably slow, not even as a cosmic scale, but on earth.
We cannot play competitive multiplayer games globally, without 300ms ping. I dream of a world playing Black Ops 2 on a original PS3 in 2026 getting into a lobby because latency is low.
How do you arrive at 300ms?
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On the other hand think of the wavelength of light and how absurdly fast the oscillation frequency is to provide a wavelength of a few hundred nm at the speed of light. 8 minutes is a lot of cycles, and 150M km is a lot of wavelengths!
For the photon the time passed is 0 right?
But light is not really even light except at human inference level. Like yes if you were a god like being looking at this and understanding light in a proton level way, it wouldn't be very impressive but I would say that is not the right way to think about physcial phenomena. How can you even be sure time has any definite meaning outside human's concept of it? In that sense what do words faster or slower or minutes even mean
No doubt inspired by George Gamow's Mr.Tompkins in Wonderland (https://en.wikipedia.org/wiki/Mr_Tompkins). That was recommended reading for entering Physics undergrads when I did my degree.
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.
Interesting this has the exact same controls with slidy movement + space bar to stop. It seems likely Claude based it off of it and the other MIT game.
From further back, https://news.ycombinator.com/item?id=40332586 with 60 comments)
> A Slower Speed of Light is a first-person game prototype in which players navigate a 3D space while picking up orbs that reduce the speed of light in increments. Custom-built, open-source relativistic graphics code allows the speed of light in the game to approach the player’s own maximum walking speed. Visual effects of special relativity gradually become apparent to the player, increasing the challenge of gameplay. These effects, rendered in realtime to vertex accuracy, include the Doppler effect (red- and blue-shifting of visible light, and the shifting of infrared and ultraviolet light into the visible spectrum); the searchlight effect (increased brightness in the direction of travel); time dilation (differences in the perceived passage of time from the player and the outside world); Lorentz transformation (warping of space at near-light speeds); and the runtime effect (the ability to see objects as they were in the past, due to the travel time of light). Players can choose to share their mastery and experience of the game through Twitter. A Slower Speed of Light combines accessible gameplay and a fantasy setting with theoretical and computational physics research to deliver an engaging and pedagogically rich experience.
The speed of light, wave-particle duality, and so on, always make me feel that the universe also has a "computing power"
Interesting experiment! What I missed (as a non-scientist) is a live explanation of what is happening while I'm navigating this virtual world and changing parameters. This would be a great way to learn!
Too bad that it does not seem to work on mobile. I did not find any way to move around (add arrow buttons? Are we supposed to move around?) and if I double tap I change the direction in which I am looking but not very predictably. Maybe my phone is too slow.
There is a mobile version https://news.ycombinator.com/item?id=49638121
It would be nice to add controls for mobile.
https://relativity-park-mobile.kshmir.chatgpt.site/
MIT Game Lab made a take on this back in 2012.
https://gamelab.mit.edu/games/a-slower-speed-of-light/
Discussed a few times:
A Slower Speed of Light (2012) - https://news.ycombinator.com/item?id=4714779 - Oct 2012 (1 comment)
I ran into this a while back when I was trying to design an RTS with information delay.
Loved that game!! Blew my mind in my 1st year physics classes
It seems like it's open source, and that it splits the game from the actual engine, so if someone wants to vibecode something of their own, they can take this as a base rather than vibing the physics from scratch, with the risks of messing the core mechanic from scratch.
I feel like a rule of vibecoding would be that you shouldn't do it for the core of a product, the quality is just not there yet. Even if it is, your core contribution should be what LLMs would train on, rather than being their output.
Played around with this one before. Very interesting. Thanks for linking it.
Feature request: I'd like to ride the ferris wheel.
The book Redshift Rendezvous from 1990 explores this idea. (TBH the story is a little clunky, but if you like to see someone look at the physics in depth, it's pretty interesting.)
https://www.goodreads.com/en/book/show/1382560.Redshift_Rend...
I'm reading the clockwork rocket at the moment. It's a little different but it's set in a universe where the laws of physics / behaviour of light seems to be different to our own.
similarly, Einstein's Dreams is a collection of very short stories that explore different flavors of time. For example: time slows as you near the city center - those who approach it end up frozen forever like the event horizon of a black hole.
https://en.wikipedia.org/wiki/Einstein's_Dreams
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
I'm being vague to avoid spoilers, but I'll just say that it serves for a very interesting meditation on the concept of loss, and has stuck with me for the 5+ years since I read the trilogy.
Same here, the quote on time passing stuck with me quite a bit.
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.
It's not actually that the speed of light in a singlemode fiber optic cable is slower, but that the photons aren't travelling in a direct path down the fiber like water down a pipe. They're bouncing off the interior walls of it at like a 45 degree angle billions/trillions of times before it reaches the other end of the cable.
Basically imagine like if you wanted to walk in a straight line between two points at both ends of a empty, long, narrow rectangular warehouse, and instead of walking in a straight line from A to B, you bounced off each wall at an angle (like a pool ball ricocheting off the bumpers) to get from one end to the other. Making your cumulative distance travelled on foot much greater.
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You're conflating two very different meanings of "the speed of light". Confusingly, "speed of light" can refer to the universal constant, c, which does not change in glass, or to the speed that light travels in a medium. Here, we're talking about c. Relativistic effects are based only on c. The Three Body Problem trilogy plot device is also about c.
Fun fact: given that the meter is defined in terms of speed of light (and cesium frequency), "changing the speed of light" is a counterfactual impossibility, what is actually changing are some other fundamental constants.
If we realized tomorrow we had the speed of light slightly wrong, we wouldn't change the length of a meter, we would change the definition of the meter. We've redefined the meter thrice already.
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.
So how do you explain that light can be slowed down?
I think the old SciFi classic "Zone of Thought" and the other book which name escapes me now explorer this idea, although not 5Km/h.
To stop a 'blight' in the universe, some natural laws have to be changed wherever it starts to spread, is the story premise if memory serves me.
The third volume of « Three body problem » and its fan-written and author-approved sequel deal with those local physical constants changes !
"A Fire Upon the Deep" and "a Deepness in the Sky" by Vernor Vinge
Deepness in the Sky "programmer-archaeologist" will never come to pass because of LLMs :(
The Forever War series changes the speed of light at the end to mess with the mortals, not to prevent any calamity however.
Btw there is also this
https://en.wikipedia.org/wiki/A_Slower_Speed_of_Light
The first few Discworld books explore this a little bit too. I think pterry dropped the concept after that, I don't really remember it later in the series.
Darkness travels even faster than light on Discworld, because it has to be fast enough to get out of the way when light arrives.
Hmm, by some bug my back arrow first slows me down from approaching c, but then will sudddenly spead me back up (while going backwards), so I get stuck in a dark world. (Firefox on Linux).
Edit, maybe it's because the speed shift is so coarse I cross past 0 km/h from back to forwards and reverse too fast...
Other than this, very very nice. Love this kind of thing for developing intuiting outside the normal range in which we experience the laws of Physics. Well done.
> my back arrow first slows me down
That's exactly what would happen ins space.
On some more testing, I don't seem to alter direction, just suddenly start to accelerate again. Ah well, it worked mostly.
Very related Scott Manley video that discusses and simulates the same effects https://www.youtube.com/watch?v=R_g9EeT233Q
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.
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.
FWIW, the best traveling speed is 147000km/h, because the Doppler effect makes a red light appear green. ;)
Awesome, at 5 km/h it feels like I'm in a black hole. Time stops at the speed up light if I'm not wrong!
Which parts of this were ideas you came up with yourself?
It’s Astra ui and graphics. I recognise it after only having seen 3 examples…
This is awesome. I always think about this. As humans, we are very limited in what we can perceive and experience. A higher form of entity could have a completely different way of viewing nature and the world.
Just a thought experiment for you guys: imagine a bacteria that survives inside humans. It doesn't even know what a human is. For the bacteria, its entire world is simply the environment in which it lives. It doesn't know that we are living beings actively trying to maintain ourselves and survive.
Now, suppose a harmful bacteria enters our body, makes us sick, and we take medicine that kills all of them. From the bacteria's perspective, it could look like a natural disaster or some unexplained event in which they all suddenly get wiped out. They have no idea that a living being called a human actively tried to eliminate them using something called medicine, which was engineered specifically to kill them.
Similarly, what if our world, or nature itself, is part of some higher-level entity that we simply exist within? What if the reason for our deaths, natural calamities, and other events is something completely beyond our perception? Whatever we do, we may never be able to understand what is actually happening at that level, just as bacteria may never be able to understand that humans exist.
One thing that could potentially support this idea is self-regulation. We see self-regulating systems throughout nature, and these patterns seem to repeat at different scales. We ourselves are self-regulating organisms, and nature also has countless cycles and mechanisms that regulate themselves.
Maybe these patterns continue at scales we cannot perceive. We can observe certain things at the scale of humans, but we still don't fully understand what happens at the nano scale or on the scale of the universe. Perhaps there are higher levels of organization and self-regulation that we simply don't have the ability to perceive yet.
Woah your reply feels very much like Deja Vu to me - my OP on X from months ago
Gitanjali GulveSehgal @gigi_sehgal Jun 22 Replying to @fermatslibrary Contrarian Takes: 1. We live in a “box” governed by the compute we are capable of. Perhaps the rockets are out there in a form we cannot observe. ( borrowing from Quantum Ruliad ). E.g What do bacteria think of us? Do we “exist” for them? Are we infrastructure or entities to them? Do they think we do not exist? We cannot see Neutrinos streaming thru our bodies but atleast we managed to figure out that they existed. Who knows what else exists that our senses and technology cannot perceive or reverse engineer existence of? 2. Perhaps they have remote observation capability, 3. Perhaps its a simulation we are in a space alien overlord’s lab 4. Perhaps the Men in Black wiped our memory each time we see them 5. What were those drones flying over DC? 6. Perhaps they are already here
Cogito ergo sum is still the only "barrier" for self-awareness, aka real knowledge.
Of course, this is what the end of Men in Black shows.
https://www.youtube.com/watch?v=OKnpPCQyUec
But let me tell you another possibility. What if there is no nature, but just our perception of it.
Yea, tree falling in the forest and all that...stated more explicitly..
That is also very much possible, we can never know. Or maybe we can in the future. Only time can tell
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
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.
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.
What you are observing is relativistic aberration. W does make your velocity increase in the forward direction.
For some reason I get a black screen in Safari. Renders ok in Brave on the same MacBook Pro.
This only works on a desktop? Is there any way to interact with it on a phone?
This is what it's like with my new glasses
Why are the lamp posts blinking in a weird way?
I think that light coming from different parts of the lamp arrives at different times. So if the lamp turns off, you see the part closest to you go black first.
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 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.
>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.
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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.
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).
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.
What if the speed of light was 2c instead of c? Would that change anything for us?
Less latency in multiplayer games or Zoom calls. Because light can travel around the Earth 7 times in one second, that means one roundtrip to a server on the other side of the world must take ~140 ms (1/7th of a second) which is a timescale you are able to feel. That's lag in multiplayer games. I'm constantly amazed that the reason why multiplayer client-side prediction strategies like rollback netcode exist is because light is slow enough on a human scale that we actually have to architect around it. Light is surprisingly slow in some ways.
The universe would look very different probably.
Now I'm curious what the evolutionary ramifications of this would be.
So weird, after visiting, my mouse icon disappears!
Then we will never be able to see aliens again.
Um, speed of light and gravity are so fundamentally linked that nothing you see would look like that. Just changing speed of light but not adjusting anything else makes little sense.
in the real world if the speed of light was 5 km, we'd probably be a lot smaller!
I don’t quite get the assumptions here. If c were actually 5 km/h, causal influences would propagate much more slowly. With G unchanged, planets and stars at their current masses and sizes would lie within their Schwarzschild radii. Any rock greater that 1.5km in radius is a blackhole. With c reduced to 5 km/h, the black-hole threshold would correspond to a surface escape speed of just 5 km/h. Holding the other relevant constants fixed would also radically alter atomic structure and chemistry. It seems like a lot would change before we could be around to observe the cool redshifts. Is the reduced c being applied only to the visual effects?
cool idea, but being vibe coded doesn't inspire much confidence on whether the math or author subject understanding is correct.
As such I wouldn't base my understanding on the subject on this as-is. Which is a shame as, if it was actually hand coded I might actually use this to learn relativity, something which would otherwise be out of my reach.
A note on source code, I think committing the actual javascript code and such is a mistake at the level of committing compiled binaries to a repo. It's more useful, correct and genuine to upload the prompts used, which are the source code that generates the target code, and upon which the author and others can study and modify the program.
That said, as an idea, it reminds me of Kay's dynabook example ( https://dl.acm.org/doi/10.1145/800193.1971922 ) :
"Here look." Her fingers started to fly on the DynaBook's keyboard, altering the program she had·written several weeks before .. You justact as though the ship is pointed towards the sun and add speed!· As she spoke her ship started to fall, but not towards the sun. Oh no!..·"
If we want to move closer to that ideal, of interactive education, I don't think we can just apply the old forms and use the LLM to aid one in being the allmighty program-creator, the LLM needs to be placed at the service of the user. I can't help but seeing the usage of LLMs to generate code as misplacing this power. It's as if a new powerful metal were discovered and smiths can only think about making hammers and foundries and casts with that metal, considering it too valuable to actually use it for the products being smithed.
Would mean the biomolecular computers would be faster than electronics.
Electronics wouldnt work at all.
Can't see your website but I would think everything you see would have so much latency it would be worse than today's internet with dialup using 2GB of RAM on an Atom CPU ;)
Next step, taking into account effects of acceleration according to general relativity.
this is really great
I think this is not possible. There is most likely a reason as to why light has this speed. Naturally it must be tied to energy and interaction of energy with other things. I also don't think "human speeds" applies here because it assumes that humans were decoupled from this, which I don't think we are at all. Besides, humans also use fairly fast things once you go down to the level of molecular biology and chemistry; the chromophore 11-cis-retinal is quite fast in its changes, for instance, and various enzymatic reactions such as by the carbonic anhydrase - up to 10⁶ reactions per second for the latter (assuming there is a sufficient amount of substrate available). That's not slow.
You wouldn’t be able to see shit OP