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

Post by fwip » Thu, Sep 10, 2026, 4:25 PM UTC

davidoduk wrote: post #228

santiagobasulto wrote: post #90

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,…

So when we think we're looking at Andromeda today, we're actually seeing Andromeda as it happened 2.5 million years ago. That means someone/something? in Andromeda today, with the ability to see Earth clearly, would see some of our ancestors, like Homo habilis. I've always wondered, if we end up being able to travel faster than light, we'd technically be able to look into the past depending on how far we go. 1000 lig…

Post by rrr_oh_man » Thu, Sep 10, 2026, 4:39 PM UTC

chungy wrote: post #213

rrr_oh_man wrote: post #193

Earlier quoted context omitted.

Can you explain for dummies how... a normal person with a normal web browser should access this?

Have an IPv6 connection.

Post by Sohcahtoa82 » Thu, Sep 10, 2026, 5:02 PM UTC

no_multitudes wrote: post #226

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.

> If you can somehow accelerate/decelerate at a constant human-acceptable 1G Well, you also need clarketech heat dissipation and collision deflection technology, if you want to get there without vaporizing.

Post by IAmBroom » Thu, Sep 10, 2026, 5:09 PM UTC

evanb wrote: post #202

timoth3y wrote: post #181

I know this takes the fun out of it, and it is a fun project, but FWIW the speed of light is not an independent variable. It's woven into the fine-structure constant, the relationship between mass and energy, and how any kind of information is transmitted between objects in the universe. This is more of a simulation of what if light was perceived as 5mph for you and kept the same for everyone else. It is cool though.

You can adjust the speed of light and hold the fine structure constant (and all other dimensionless parameters) fixed by adjusting some of the other dimensionful parameters.

Post by IAmBroom » Thu, Sep 10, 2026, 5:14 PM UTC

somenameforme wrote: post #190

rootusrootus wrote: post #35

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.

I wish the guy who created this included a ' your perceived velocity relative to [some fixed point]'. The speedometer shows what an at rest observer would perceive your velocity as, not what you would perceive it is. The 'magic' of relativity is that the speed of light is not really a speed limit. You can travel endlessly far ahead of it. Distance and time then begin to distort, and you effectively travel into the fu…