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

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

#251

Post by andruby »

Terr_ wrote: post #140
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,…

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.

You're right, but not entirely.

At 1G constant acceleration reaching Andromeda would take ~15 years, or ~29 years if we also need to decelerate at the same 1G rate to not just whoosh by.

The furthest known galaxy is MoM-z14, which would take ~47 years to reach.

But unlike Andromeda, MoM-z14 is accelerating away from us, or more precisely, the space between us and MoM-z14 is expanding. It's "receding" at 726,000 km/s (= 2.4 times the speed of light). And still accelerating. Because of these, even the magical constant 1G accelerating spaceship can never reach it, not even in 1 Billion years.

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

#252

Post by GPerson »

qurren wrote: post #30
bilekas wrote: post #19

Earlier quoted context omitted.

Are you trying to tell me time is relative?

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.

This is not correct. The stated age of the universe is measured relative to the rest frame of the CMB, the standard preferred frame in cosmology.

People working at AI labs like yourself should figure out how to stop destroying science so there are still people who know enough to call you out when you spread misconceptions.

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

#253

Post by SideburnsOfDoom »

ExoticPearTree wrote: post #124
marcyb5st wrote: post #106

Earlier quoted context omitted.

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 r…

> 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?

> Can't we accelerate past 1G constantly?

It's hard to accelerate at or beyond 1G for very long with current technology. Roughly speaking, the rocket runs out of fuel soon. Packing more fuel makes the rocket heavier, meaning diminishing returns when using the fuel. The mass required grows exponentially. See "The tyranny of the rocket equation"

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

#254

Post by hebelehubele »

Terr_ wrote: post #140
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,…

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

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

#255

Post by Terr_ »

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

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.org/wiki/Neutron_Star_(short_story)

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

#256

Post by domhudson »

Really cool! Are you able to add an indicator showing which direction you're travelling in? It's quite confusing to start due to all the effects.

I also recommend a banner that says it doesn't work on mobile as it was quite confusing to me as to whether it was working or not.

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