Show HN: What if the speed of light was 5 km/h? • Hacker News Board

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

#261

Post by sh0gg0the » Thu, Sep 10, 2026, 9:25 PM UTC

shagie wrote: post #196

sh0gg0the wrote: post #169

Earlier quoted context omitted.

On YT there is a video of a flight through the solar system at the speed of light starting at the Sun. It's a pretty boring video. You see very little movement and change over time. After 8 minutes Earth slowly passes by. After 44 minutes you reach Jupiter and the video ends.

If The Moon Were Only 1 Pixel (A tediously accurate scale model of the solar system) https://www.joshworth.com/dev/pixelspace/pixelspace_solarsys... has a button at the bottom right for 'C' which scrolls to the right at the speed of light on that scale. https://thinkzone.wlonk.com/SS/SolarSystemModel.php?scale=10... lets you make scale model calculations (useful if you're building one). The default model scale has th…

Does this take relativistic effects into account? The video I mentioned doesn't. Near the speed of light your surrounding looks like sped up and the distance to your target is clinched. Your own time runs slower in comparison and the distance is shorter. So theoretically you're able to reach the destination millions of LY away in your lifetime.

Edit: I now watched the animation. It's exactly the same as the YT video. Speed of light is very, very slow.

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

#262

Post by MathMonkeyMan » Thu, Sep 10, 2026, 9:31 PM UTC

rrr_oh_man wrote: post #233

chungy wrote: post #213

Earlier quoted context omitted.

Have an IPv6 connection.

So basically "go fuck yourself" if your ISP does not yet support IPv6? I'm not saying that I couldn't fire up Cloudflare Warp, but I think it's a legit issue for average users [0]? [0] https://xkcd.com/2501/

Funnily enough, I use Cloudflare Warp at work, and it breaks my site for what I think are DNS related reasons. Maybe there are some more exotic DNS keys that I need to add.

Or I could go back to IPv4 with dynamic DNS, but that would mean changing domain registrars.

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

#263

Post by [deleted] » Thu, Sep 10, 2026, 9:39 PM UTC

hebelehubele wrote: post #254

Terr_ wrote: post #140

Earlier quoted context omitted.

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.

There was a bit in the series "The Expanse" about a what's called "Epstein Drive" where some guy invents a propulsion tech based on fusion and he losts control of his aircraft under an ever-increasing acceleration. After some minutes, his body gets crushed under its own weight before he could reach the controls and slow the spaceship down. https://www.youtube.com/watch?v=1lS_WxQ3zeU

[deleted]

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

#264

Post by lostlogin » Thu, Sep 10, 2026, 11:54 PM UTC

rrr_oh_man wrote: post #150

lostlogin wrote: post #133

Earlier quoted context omitted.

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

> "Increasing the acceleration a little bit more than that (eg to 1%) would make a difference." Wouldn't that be only a few months on a decades-long journey at 1.01G vs 1G??

I was thinking of journeys that are hundreds or thousands of years.

If the acceleration was too great but survivable, what happens? I can’t imagine my back, knees or ankles would like it.

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

#265

Post by 93po » Fri, Sep 11, 2026, 12:03 AM UTC

jmaw wrote: post #194

fahrvrgnugen wrote: post #58

Earlier quoted context omitted.

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

Simply send your cable through the center of the earth and boom, latency reduced by ~1/2. Remember me when you make billions of $ from my idea.

It'd actually be about 36% shorter :)

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

#266

Post by zem » Fri, Sep 11, 2026, 12:16 AM UTC

Terr_ wrote: post #255

hebelehubele wrote: post #254

Earlier quoted context omitted.

There was a bit in the series "The Expanse" about a what's called "Epstein Drive" where some guy invents a propulsion tech based on fusion and he losts control of his aircraft under an ever-increasing acceleration. After some minutes, his body gets crushed under its own weight before he could reach the controls and slow the spaceship down. https://www.youtube.com/watch?v=1lS_WxQ3zeU

Yeah, certainly a reason to have failsafe timers and dead-man switches when testing new things. While I did read The Expanse , when I think of that class of dangers, what pops to my mind is an old short story Neutron Star (1966) [0]. A financially desperate pilot is hired to discover what killed some researchers while leaving the indestructible starship hull intact... and the thrusters off. [0] https://en.wikipedia.o…

there was an interesting retcon of that story in one of niven's later works, where it was pointed out that any spacefaring race would know instantly what killed him. it was just better PR to pretend that it was a huge mystery, and that their hull wasn't vulnerable to some stupidly obvious danger but rather to something no one could have foreseen.

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

#267

Post by alok-g » Fri, Sep 11, 2026, 12:22 AM UTC

Ajedi32 wrote: post #192

somenameforme wrote: post #191

Why is everything black when I turn around at high velocity?

Because the doppler effect shifts all light coming from that direction to infrared, which your eyes can't see.

Would the photochemistry of my eyes stay the same? :-)

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

#268

Post by digitalsushi » Fri, Sep 11, 2026, 12:29 AM UTC

stouset wrote: post #250

jtbayly wrote: post #247

Earlier quoted context omitted.

I’m confused. Is it 11k years to the closest galaxy at the speed of light, or somehow accessible in a human lifetime?

Relativity is weird. If you keep accelerating, at some point the objects stop accelerating toward you faster but the distances get shorter. To an outside observer, the trip might have taken you millions or billions of years while to you it was only ten or twenty. It’s helpful to think about the limit. To light, which travels at the speed of light, it arrives at your retina the exact moment it was created in the core…

yeah but its statistical luck, a few photons keep winning the roulette wheel and pop out very quickly; and a few unlucky ones are still rattling around in there from year 1! it's more like winning a raffle than waiting in a queue

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

#269

Post by jtbayly » Fri, Sep 11, 2026, 1:57 AM UTC

stouset wrote: post #250

jtbayly wrote: post #247

Earlier quoted context omitted.

I’m confused. Is it 11k years to the closest galaxy at the speed of light, or somehow accessible in a human lifetime?

Relativity is weird. If you keep accelerating, at some point the objects stop accelerating toward you faster but the distances get shorter. To an outside observer, the trip might have taken you millions or billions of years while to you it was only ten or twenty. It’s helpful to think about the limit. To light, which travels at the speed of light, it arrives at your retina the exact moment it was created in the core…

> “At 99.999% C, the traveler would take ~11,000 years to arrive to Andromeda.”

So presumably this means 11k years from an earth point of view? But the traveler would still be alive and a very short time would have passed for him?

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

#270

Post by stouset » Fri, Sep 11, 2026, 2:46 AM UTC

jtbayly wrote: post #269

stouset wrote: post #250

Earlier quoted context omitted.

Relativity is weird. If you keep accelerating, at some point the objects stop accelerating toward you faster but the distances get shorter. To an outside observer, the trip might have taken you millions or billions of years while to you it was only ten or twenty. It’s helpful to think about the limit. To light, which travels at the speed of light, it arrives at your retina the exact moment it was created in the core…

> “At 99.999% C, the traveler would take ~11,000 years to arrive to Andromeda.” So presumably this means 11k years from an earth point of view? But the traveler would still be alive and a very short time would have passed for him?

Nope! Far, far longer. I don’t know the specifics that the GP used but Andromeda is about 2,500,000ly away. An observer on Earth must perceive you as taking more than 2,500,000 years to get there, as you would have to have exceeded the speed of light to arrive any sooner.

At 1g of constant acceleration you can reach Andromeda in just under 15 years of experienced time. An observer on Earth will perceive you as having taken a hair over 2,500,000 years to get there. You can get there arbitrarily quickly; at 10g it would take a 1 year 9 months. But an external observer on either planet will see you taking closer and closer to 2,500,000 years to make it the full distance.