Comment by Terr_
10 hours 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.
That's the premise of Tau Zero, a very good novel:
https://en.wikipedia.org/wiki/Tau_Zero
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.
There's a diagram for how long it takes a 'light-hugger' ship to travel various distances at 1-G acceleration. Shiptime is on the left, earth time is on the right. https://en.wikipedia.org/wiki/File:Roundtriptimes.png
http://www.zitterbug.net/future/future815.html
What If Light Was Really Slow? https://www.youtube.com/watch?v=ge_j31Yx_yk -- https://duckduckgo.com/?q=slower+speed+of+light&ia=videos&ia...
> 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.
Yeah, once you reach a certain speed, even colliding with a fleck of dust can obliterate a ship.
Colliding with a single 0.3 mg grain of salt at 20% of the speed of light creates an impact with 560 MJ of energy, equivalent to 130 kg of TNT, over 8 times the nuclear bomb dropped on Hiroshima.
Even a tiny speck of dust, half a microgram, is equivalent to a hand grenade when hit at 20% the speed of light.
You wouldn't be able to even escape the solar system before your shields were devoured. If you accelerated at 1G constantly, you'd be going 3.5% of the speed of light by the time you reached Pluto's orbit. Space dust particles are already hitting you like nuclear bombs at that speed.
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.
[0] https://en.wikipedia.org/wiki/Neutron_Star_(short_story)
This is a really interesting video that explores this topic, pointing out that at near light speeds, the entire universe becomes accessible in a single human lifetime.
The Overview Effekt: Time Dilation Visualized
https://youtu.be/8FT-oz9aZU4
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 of the sun. From our perspective, it took almost a million years (about a million years to make it from the core to the convective region, then another few minutes to travel from there to Earth).
Then I guess you will need millions tones of perfect mass to light converter like Astrophage just to get to the neighbor. The universe is simply too big to comprehend.