Comment by munksbeer
Comment by munksbeer 6 months ago
> Light is incredibly slow, and everything seems out of reach.
Yes, agreed. I find it a little depressing. An unimaginably huge universe, tantalisingly there, but completely out of reach.
Comment by munksbeer 6 months ago
> Light is incredibly slow, and everything seems out of reach.
Yes, agreed. I find it a little depressing. An unimaginably huge universe, tantalisingly there, but completely out of reach.
You wouldn't need a sudden jump. If you had a rocket that accelerated at a pleasant 1G forever, you could reach and stop at the center of the milky way in about 20 (your time) years, and you could reach and stop at the Andromeda galaxy in about 28 years. Play around with some of the online space travel relativity calculators--it's wild!
Of course building and fueling such a rocket is what's totally out of reach.
> Of course building and fueling such a rocket is what's totally out of reach.
We'd need a device that could efficiently transform several kg of matter to photons.
Is there drag in space? I.e. would you need increasing energy to accelerate at a constant rate as the speed goes up?
We're already on that starship. Our engine is about 8 lightminutes away. All we need is to figure out how to steer this thing - and how to not wreck it while en route.
I would prefer the concept of people building an artificial planet/asteroid/spaceship for a starship, instead of messing with our star system. But luckily that debate is some years away and currently we cannot even figure out, how to deal with some increased CO2 levels.
How would that feel as a traveler? Does all motion slow down to a crawl, all sub-atomic particles just "freeze" and essentially your thoughts and body aging too? So it would seem like you got there in an instant?
For sure you're not just sitting there watching people get born, live and die in second and shrugging your shoulders.
You’d feel nothing out of the ordinary whatsoever. The starscape outside the ship would look strange though, shrinking into a small, blueshifted patch of sky straight ahead, while stars behind you would redshift out of the visible range. Everything moving at very low speeds relative to you would indeed appear to happen really fast.
What are the chances of hitting a small meteorite or part of it, traveling now at relativistic speeds wrt you?
It depends on acceleration though. If acceleration and deceleration take long enough, it could take an entire generation to get up to a fast enough speed that relativistic effects make any difference, and another generation to slow down enough to interact with anything you might see.
Plus if you're traveling at near light speed, running into any matter at all would be pretty devastating for whatever craft you're in.
Edit: someone further down claimed that the math says that accelerating at 1G would get you to 0.1c in a month, so that's actually not that bad all in all. I still maintain that hitting any matter at those speeds might be unpleasant.
But unless you have a way of slowing down again you'll never see anything of your destination, just the briefest of flares of light as you sail past. And if you do have a way that involves anything like physics that we recognise, you've brought along a huge rest mass that then got accelerated to near light speed. Probably your civilization needs to be approaching Kardashev Level 2 to pull this off.
If you enjoy such questions, I highly recommend https://www.amazon.com/Indistinguishable-Magic-Robert-L-Forw....
The best speed for interstellar travel with technologies that current theory says should be within our reach can be achieved with a vehicle with a light sail pushed by a giant laser, that is powered by solar power. There is even a way to brake it when it reaches the target star. I forget what the predicted velocity was though.
This technology is basically the same as one that the Moties developed in the story, The Mote in God's Eye.
Slow down by pulling on the fishing line tied to the back of it, carefully.
It slows down by releasing a large light sail in front of it, designed to reflect light back to a much smaller light sail behind it. The laser then pushes the large sail away, and as the sail goes it pushes the smaller sail (and ship) back. This leaves the ship at moderate speed relative to the new star, and a large sail traveling very, very quickly beyond it.
We do not yet have this technology. But we can show that it is plausible.
According to the first Google hit, https://scitechdaily.com/nasas-parker-solar-probe-the-fastes... , the fastest we've made so far went 430k mph (falling towards the sun), or about 0.064% of c. Good guess.
We have a number! Around 0.1c maximum and unsurprisingly it involves using nuclear bombs to push yourself.
https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...
> "A photon instantly travels to the end of time"
Please explain this. TIA
First set gamma as being 1/sqrt(1-v^2/c^2), with "c" being the speed of light. The factor for time dilation and distance contraction in special relativity is gamma and 1/gamma respectively.
That means that when you get to speeds equal to c, your time runs infinitely slower and the distances are infinitely shorter. So if your clock is infinitely slower, so every travel at "c" speeds means that no time passes for you. And if your distances are infinitely shorter, all travels at "c" speeds cover any distance as immediate. So you could reach every point of the universe as if it was immediately closer and in no time at all.
So in the frame of reference of the photon, the moment it is created it has already reached its destination, be it wherever it is on the universe.
Of course we can never reach "c" as beings with mass, but we can get closer to that. So for example if you get to 99.99999999999999% of the speed of light, you could travel a distance of 54,794,520 ly and only one year would pass to you, while 54,794,520 years would pass on earth.
Follow up question from someone who's mostly forgotten his university physics.
Do photons actually exist, in the traditional sense of physical matter.
Or are they just a convenient short hand to describe the transfer of energy via waves in the fabric or space time, if they dont experience the universe when passing through it but only when interacting with matter and matters "dents" in space-time.
A very layman’s explanation I read a long time ago. Imagine you are in a car driving in a big open desert. You can drive in any direction you want. You can drive East or South or West or North, or some degree between them. But the more you travel East, the less you can travel North or South. The more you travel North, the less you can travel East or West. If you drive completely North, you aren’t traveling at all in the East/West direction.
Spacetime is like that, except North/South is space, and East/West is time. The more you travel through the spatial dimension (the faster you go) the less you travel through the time dimension (the less time passes for you). Photons are traveling completely through the spatial dimension (North/South) and so aren’t moving through the time (East/West) dimension at all, so from a photon’s perspective (if they had perception) no time ever passes so they would zip around “instantly” and never “experience” anything.
It is also why the speed of light is the fastest you can go. Once you are going 100% North, you cannot be going any more North.
That doesn’t make sense - if you were traveling at the speed of light, it would take you 5000 years to travel 5000ly - longer if you were just ‘very close’ to C. Time wouldn’t advance slowly for you, it wouldn’t advance perceptively different at all - you’d still live every second of those 5000 years.
I dont think you are right. Light for example doesnt perceive time at all. From the photons point of view it never aged even a microsecond while it traveled lightyears. Time is relative too so from our POV 1 year passed when a photon traveled 1 ly, but for the photon no time passed.
You two are talking about different meanings of "time".
Traveling 5,000 LY at 0.5 c will cause you the spaceship pilot to age 20,000 years. It's non-relativistic, inside that inertial frame. Clock second hands still sweep slow but noticeable circles.
Meanwhile, everyone outside of the spaceship is happening FAST, by your observations. You'll see stars turn red and go supernova.
10,000 years of empty space to get to the next solar system. Exciting.
Not with light speed travel. At even 1% the speed of light, the travel time diminishes significantly:
- Titan, Io and Ganymede are only 2.5 days away - Pluto is about 23 days
Edit: Even at such speeds, we still can’t visit a nearby star system in a reasonable time-frame. Oh well.
As time passes, the universe is expanding infinitely in every direction from every point.
Even if we could travel at 1 percent the speed of light, the "destination" would be inflating away from us at much greater relatavistic speed.
To your point, this is less an issue with solar or extra solar objects.
Doesn't this depend on the initial distance to the destination? I'm thinking you have to be going ~140M light-years for cosmic expansion to exceed 1%c, and Proxima Centauri is only ~4 light-years away
Speaking of which, Peter Watts' Sunflower Series has a great and short enough hard-ish scifi story about just such a ship.
We can instead happily drive our solar system in a different direction by nudging the sun.
At this point in humanity's history, I think that's more feasible than high speed traveling.
It makes me wonder what kind of "life" could perform interstellar travel? I used to imagine a spaceship being alive, with people inside being analogous to "cells" in a multicellular organism.
Perhaps this is really how AI achieves consciousness?
To make a generation ship work you have to build a self-contained ecology that is stable and self-repairing, inside mechanical and software systems that are fault tolerant and either extremely redundant or self-repairing, run by a political and social system that is also fault-tolerant and self-repairing.
We know how to do exactly zero of those things.
More to the point the ship needs to be absolutely self sufficient, it can't even use solar power and has no access to outside mass whatsoever. But if you have a ship like this you could build an orbital habitat using the same technology, and it would be much much easier to build since it doesn't have to accelerate, can use solar power, and has access to the rest of the resources of a solar system.
If you have all of this why would you go to the enormous extra effort to move the habitat to a different solar system? Even if your civilization is so old that the star is a dim brown dwarf that's still plenty of energy for day to day life.
There's a CRPG I've been meaning to play where this is basically the plot; there was a generation ship, it was heading towards some planet or another, but the social and political structure on the ship broke down at some point and now there's no one actually in charge, the ship is getting run down, and they probably blew past their destination a hundred years ago if they were even still on course at all.
I remember someone pointing out that a generation ship could be problematic because you have one generation who decides to launch this expedition but will never see the end, multiple generations who didn't choose this life and won't get to see the benefits, and then one generation who actually gets to the planet but might not even want to be there. Without some kind of cryogenic sleep or relativistic speeds the whole thing might fall apart just because most of the people involved "didn't sign up for this" but they have to toil away anyway for someone else to benefit from it.
Well, to be frank, we currently have such a ship, but we're doing quite a lot to disrupt its capability of sustaining human life.
Of course, even if we stopped doing that, we'd need to figure out how to visit another place if our ship is passing close by. That also seems to pose a problem: both Voyagers are barely out of the exhaust fumes of our ship's motor, and getting so far took ~40 years.
It's a wonderfully entertaining book and for that reason I loved it, but Andy Weir really, really glosses over and hand-waves away all kinds of other difficulties for so quickly and easily building a ship that can travel at nearly the speed of light.
He basically just has it work because the fuel difficulties are solved and bam, the main character can zip around nearby start systems at close to perfect C on a ship built with little more than our current 21st century technology. Fun, but not even in the most basic way an attempt at presenting any science seriously.
What makes it more amusing is that for many other parts of the main drama, he puts a lot of effort into making the descriptions and scenarios seem as realistic and science-rich as you could like. I suspect a lot of entertaining word salad there too though.
Not really, because it was a single person and the spaceship was a vehicle. The other race was still in a vehicle.
Think more about the difference between single celled organisms versus a multicellular organism: IE, the spaceship itself is alive and has a lifespan where interstellar travel is a fraction of its life. The people inside are like cells inside our body.
Not out of reach if you get very close to light speed. Time would advance very slowly for you, so counterintuitively it is possible to travel 5000ly in your life time.
Although for everyone else at least 5000 years will pass, so better say goodbye to family and friend.
Hm, not sure if that is really less depressing...
Also light isn't slow. A photon instantly travels to the end of time and yet it still takes a few minutes from the surface of the sun to us. Or about 100000 years from the center of the sun to its surface.