Show HN: What if the speed of light was 5 km/h? (rivendell.dmitrybrant.com)

308 pointsby dmitrybrant8 hours ago137 comments

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!

adamkurkiewicz 3 hours ago

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.

santiagobasulto 3 hours ago

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.

atlimar 2 hours ago

> 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?

santiagobasulto 2 hours ago

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

desterothx an hour ago

The speeds are theoretical (unachievable), time dilation itself is robust and proved (gps wouldn't work as precisely without accounting for it)

ndsipa_pomu 2 hours ago

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.

ryeights 2 hours ago

Proper time asymptotically approaches zero here right?

marcyb5st 2 hours ago

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.

rrr_oh_man an hour ago

> math get's really counterintuitive to grasp

People always say that about speed of light stuff, but I don’t get it. Do you have any more examples of counterintuitive math?

Because what you’re describing is basically the equivalent to compound interest in finance. (e.g. investing $100 at 10% interest over 10 years results in $260)

jeanlucas an hour ago

One million seconds is 11 days, a billion seconds is 31 years.

rrr_oh_man 36 minutes ago

Thanks! But same here imho:

              1,000 seconds =          ~0.01 days (~17 min)
          1,000,000 seconds =         ~11.57 days (~12 days) 
      1,000,000,000 seconds =     ~11,574.07 days (~32 years)
  1,000,000,000,000 seconds = ~11,574,074.07 days (~32k years)

It all seems quite logical once you put everything into the same unit, I think.

Maybe it's just our human calendar/time unit rollercoaster (60*60*24*30*12) that's playing tricks on us here.

jeanlucas 12 minutes ago

Of course it is logical, we are not discussing the math.

But it isn't intuitive, you're not used to numbers that big or that grow that fast.

Few things go from a million to a billion, especially when related to time.

MathMonkeyMan 27 minutes ago

The proper time (that is, the time the traveler measures on a clock) goes to zero very quickly towards the end. Even with both axes plotted logarithmically, it's just a sudden drop at the end towards light speed.

- [pic](https://home.davidgoffredo.com/hackernews/proper-time-one-li...)

- [plot](https://home.davidgoffredo.com/hackernews/proper-time-one-li...)

ExoticPearTree an hour ago

> If you accelerate at 1g constantly for 1y you travel 0.5 light years

Can't we accelerate past 1G constantly? Or do we expend so much energy doing it that we can't realistically do it with today's technology?

mjmas 37 minutes ago

We can't necessarily survive that well when under acceleration greater than 9.81 metres per second per second for extended periods of time.

lostlogin 24 minutes ago

Gravity on Earth varies about .7%.

Increasing the acceleration a little bit more than that (eg to 1%) would make a difference.

https://en.wikipedia.org/wiki/Gravity_of_Earth

wallst07 37 minutes ago

We can easily accelerate past 1g... 1g is just chosen for human comfort, but running any rocket engine continuously for a year requires an impossible amount of fuel.

jdjfbfbdbfnf 24 minutes ago

We need a massive rocket to escape the earths gravity (1g). That takes us minutes and a crap ton of fuel. The issue is to keep doing that with fuel and oxidiser constantly for 1, 2 or 10 or 25 years is a monumental amount of energy, which is a monumental amount of weight, which is a monumental amount of volume... Also you also need the exact same amount of fuel to stop again.... So yeah ... We don't got it yet

TheOtherHobbes 11 minutes ago

We can't do it with any rocket-like propulsive technology. By the time you get anywhere close to c the front of your spacecraft is being abraded into nothing by interstellar gas, larger particles of dust will kill you, and colliding with anything bigger creates an explosion that can be seen for light years. You need to be flying a large asteroid to even think about surviving it - you still won't for long, but you will have time to think about it - and the energy requirements are wildly impractical.

Magic warp bubble tech is the bare minimum, and we're nowhere close to inventing that.

myrmidon 8 minutes ago

Sadly there is no realistic approach to get there (even assuming fantasy-levels of technology).

Chemical rockets are currently the only thing that allow sustaining such accelerations briefly for human-size payloads, but the low exhaust velocity and exponential reaction mass requirement make sustaining it for days/months/years completely impossible.

You'd have to supply the energy externally (i.e. some sort of beam propulsion), but getting any significant fraction of g out of such a system (with human-sized payloads) seems unlikely within the next centuries, especially as the distance increases.

alex_duf 21 minutes ago

You can but I don't want to see that energy bill

buf an hour ago

Not only that, from light's perspective, it takes no time at all. ;)

irjustin 28 minutes ago

From the light's perspective: "what is this.... time you speak of?"

Terr_ 9 minutes ago

In terms of comparisons to human lifespan, I think this one is interesting:

If you can somehow accelerate/decelerate at a constant human-acceptable 1G, time dilation means almost anywhere is reachable in a human-lifetime.

That coincidence(?) could easily become false if we are accustomed to lower accelerations or lesser lifespans.

gigisfndr 16 minutes ago

This is an awesome thought provoking question! My mind goes immediately to perhaps using this as a “time scaled” model to “observe” well known physical experiments and physical phenomenon if possible eg Young’s Experiment. Could that work / be useful? I am not a physicist but currious.

greysphere 3 hours ago

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?

dramm 2 hours ago

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.

rootusrootus 6 hours ago

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.

HDBaseT 5 hours ago

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.

zelphirkalt 5 hours ago

How do you arrive at 300ms?

fahrvrgnugen 4 hours ago

light is 186k miles per second, the other side of the globe is 12.5k miles away - so 67 ms / 130ms+ round trip in optimum conditions. Add more for network hops and consider that fiber is not quite as fast as vacuum.

300ms feels extremely optimistic coming from my perspective of someone living on an island in SE Asia

skhr0680 4 hours ago

For a city that is far away from anywhere:

https://wondernetwork.com/pings/Auckland

Your real world latency is going to be worse.

esikich an hour ago

This is a great example of information taking time:

https://www.ibiblio.org/harris/500milemail.html

jbaber 5 hours ago

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...

altmanaltman 3 hours ago

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

HPsquared 2 hours ago

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!

brontosaurusrex 2 hours ago

For the photon the time passed is 0 right?

tristanj 7 hours ago

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.

shagie 6 hours ago

From further back, https://gamelab.mit.edu/games/a-slower-speed-of-light/ and https://theandelope.itch.io/a-slower-speed-of-light (https://news.ycombinator.com/item?id=4731749 284 points by po on Nov 2, 2012 with 106 comments and in 2024 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.

koolala 6 hours ago

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.

gryfft 7 hours ago

It would be nice to add controls for mobile.

kshmir 6 hours ago

https://relativity-park-mobile.kshmir.chatgpt.site/

tomjakubowski 7 hours ago

MIT Game Lab made a take on this back in 2012.

https://gamelab.mit.edu/games/a-slower-speed-of-light/

chamomeal 6 hours ago

Loved that game!! Blew my mind in my 1st year physics classes

Tostino 6 hours ago

Played around with this one before. Very interesting. Thanks for linking it.

hn993302 5 hours ago

I ran into this a while back when I was trying to design an RTS with information delay.

TZubiri 5 hours ago

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.

dang 4 hours ago

Discussed a few times:

A Slower Speed of Light (2012) - https://news.ycombinator.com/item?id=40332586 - May 2024 (59 comments)

What if we could reduce the speed of light - https://news.ycombinator.com/item?id=26309517 - March 2021 (1 comment)

A Slower Speed of Light (2012) - https://news.ycombinator.com/item?id=17169262 - May 2018 (15 comments)

A Slower Speed of Light - https://news.ycombinator.com/item?id=4731749 - Nov 2012 (105 comments)

"A Slower Speed of Light" Game Trailer - MIT Game Lab - https://news.ycombinator.com/item?id=4714779 - Oct 2012 (1 comment)

pmontra 4 hours ago

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.

lysium 4 hours ago

There is a mobile version https://news.ycombinator.com/item?id=49638121

the-mitr 6 hours ago

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

divyekapoor 6 hours ago

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.

walrus01 6 hours ago

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.

taneq 6 hours ago

Light’s still slower in glass than in a vacuum, though, or it wouldn’t refract at the transition between the two.

walrus01 6 hours ago

Right, and it varies with what type of glass, google "refractive index of glass".

If you google image search "refraction fiber optics" you'll get some decent pictorial examples of what I meant by photons bouncing off the interior walls of a 9/125 SM fiber optic strand billions/trillions of times on its path, I guess I was trying to write an extremely simplified explanation of refraction in something like a typical SMF-28e / G.652.D fiber.

rootusrootus 6 hours ago

> 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

At the risk of exposing how little I remember from physics, doesn't light in a single mode fiber not bounce? (right about now I'm thinking that it's probably not great to think of photons bouncing because this is quantum level stuff, right? light is a wave, etc. gosh it's been a long time since I tried to really know any of this...)

walrus01 5 hours ago

The bouncing is more a metaphor, the refraction of light bending at an angle is sort of like how if you as an exterior observer look at a person who is standing waist deep in a very calm and clear swimming pool, their legs appear to be at a different position than their torso. Now imagine that 'bending' repeating trillions of times.

https://www.aflhyperscale.com/articles/how-do-fiber-optics-w...

vlyan 5 hours ago

>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.

I know there are many other mundane technologies that can be described in sci-fi-ish way, but for some reason I'm particularly amazed by fiber transmitters being compact and cheap enough to be used in mass-produced killer drones.

walrus01 4 hours ago

Not just that but your average russian or ukrainian used expendable munition UAV that uses a singlemode fiber spool uses the cheapest and most mundane of fiber transceivers. There's no requirement for data rates above 1 Gbps, so ordinary SFP optics (not SFP+ or anything) are used, and the distances involved means it works fine with a extended range 1550nm to 1610nm reach thing that can nominally handle 40 to 80 km of fiber.

When I say data rates are way below 1 Gbps, it's because commonly you've got two things going on, a UART serial bridge from operator to flight controller board (same idea as what is implemented in RF with ExpressLRS, TBS Crossfire or similar), this is at most a Mbps or two. Then a possible live video feed over IP which will be easily under 50 Mbps.

The only thing a little bit out of the ordinary about them is that they're often bidirectional single strand optics with the prism built in, and tx/rx on different wavelengths (like 1550 and 1570, or 1550 and 1610, or whatever). Basically same thing that somebody lighting a very low cost metro dark fiber circuit might do to use only 1 strand for a gigabit or 10 Gbps link.

sampullman 4 hours ago

You can get a pretty good 1080p60 video at only 6mbps. Depends on how well the sender is encoding I guess, but it shouldn't be too much more than that.

tliltocatl 3 hours ago

I think the drones don't use a complex encoder because latency.

walrus01 2 hours ago

Some of the more basic ones are a very rudimentary NTSC analog video in to H264 encoder board that is tiny in weight and power consumption. They're using the same NTSC analog video-out forward flight cameras as are used in pure analog FPV. It's also not doing really 'complex' H264 encoding. Very similar to what you would get for the H264 encoder in a cheap $60 IP (RTSP) security camera.

There's more advanced ones that take video input from a MIPI digital video interface or native HDMI input.

Not just because latency but also because of cost, size, weight, power.

nearbuy 5 hours ago

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.

aaronbrethorst 6 hours ago

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.

er4hn 6 hours ago

Same here, the quote on time passing stuck with me quite a bit.

IvyMike 4 hours ago

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...

nielsbot 4 hours ago

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

jcul 3 hours ago

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.

throwaway893257 15 minutes ago

This looks oddly similar to a psychedelic trip.

tliltocatl 3 hours ago

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.

sakjur 3 hours ago

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.

nico_bresson 2 hours ago

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!

jjgreen 35 minutes ago

What if the speed of light were 5 km/h?

TheOtherHobbes 4 minutes ago

Nothing would work, including us, because almost everything in physics and biochemistry works at higher speeds.

Whether or not the speeds at which things happen in physics, chemistry, etc are somehow absolute, or somehow inherently relative to c, and would speed up and slow down if c changed, is an interesting question.

linzhangrun an hour ago

The speed of light, wave-particle duality, and so on, always make me feel that the universe also has a "computing power"

bananaflag 7 hours ago

Btw there is also this

https://en.wikipedia.org/wiki/A_Slower_Speed_of_Light

mjdv 2 hours ago

Feature request: I'd like to ride the ferris wheel.

zrail 7 hours ago

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.

yreg 3 hours ago

Darkness travels even faster than light on Discworld, because it has to be fast enough to get out of the way when light arrives.

teekert 4 hours ago

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.

classified 4 hours ago

> my back arrow first slows me down

That's exactly what would happen ins space.

teekert 4 hours ago

On some more testing, I don't seem to alter direction, just suddenly start to accelerate again. Ah well, it worked mostly.

janandonly 3 hours ago

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.

chantepierre 3 hours ago

The third volume of « Three body problem » and its fan-written and author-approved sequel deal with those local physical constants changes !

messe 2 hours ago

"A Fire Upon the Deep" and "a Deepness in the Sky" by Vernor Vinge

seanmcdirmid 2 hours ago

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.

zkmon 2 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 an hour ago

So how do you explain that light can be slowed down?

zkmon 41 minutes ago

The same way as we talk about it's speed and travel etc - using higher level human perceptions.

rx_tx 3 hours ago

Very related Scott Manley video that discusses and simulates the same effects https://www.youtube.com/watch?v=R_g9EeT233Q

aadyachinubhai 5 hours ago

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!