Comment by amelius 4 days ago
Make sure you press the "c" button in the bottom right.
Light is incredibly slow, and everything seems out of reach.
I think we'll have a holodeck before we reach another star. And maybe that'll be enough.
Light is comparatively and objectively slow in comparison to the distances that exist. Andromeda is 1M light years from us. From that perspective, 300k kph is oddly slow actually. I love the passion that you're brining to the table though. It reminded me of the blue giant stars whose lifespans can be as short as tens of millions of years, more often hundreds though. For billions upon billions, I suppose that would be white and brown dwarfs. Although, if we could orbit black holes and harness the energy of gravity, then we're really talking long time scales. Cracking the aging problem would allow us to think in very long timescales. But I do wonder whether the human psyche could handle such long lifespans.
> in comparison to the distances that exist
This leaves out the time component. Who's to say that a year is long? A galaxy a million light years away takes a million years to reach... and maybe that's a short amount of time, to the right observer.
There's a great video is saw. In 30 minutes it goes through the entire lifespan of the universe.
Even after all the stars die, the white dwarfs will continue to glow. And after eons, the last black holes will evaporate. The point is that the age of stars is only a tiny fraction of the lifetime of the universe. Maybe the speed of light makes sense at that scale.
But... I'm not happy with that theory. In a relatively short amount of time the expansion of the universe will increase faster then the speed of light. Which means it will be impossible to ever get information from the other side of the universe.
I find it very unreasonable that the universe imposes a speed limit on everything and then completely ignores it.
We have a long way to go before we learn to move a star (or a rosette).
Such an interesting perspective! It would be nice to see evolution sped up as well, or any process that seems unchanging for less than a few thousands of years.
Chances are that only a species who, through one way or another, has become very uninterested in warfare could have advanced to the point where they would be able to run such a simulation, otherwise they'd have ended their own existence with their shiny toys before long.
War only occurs if you have in the literal sense retarded elements in your advanced species and is nonsensical from an outside POV. A species this advanced would have fixed such shortcomings in itself long ago.
So no, I don't think they'd necessarily be very interested in watching primitive species go to war with primitive weapons.
For all we know the simulation of this universe is happening in their equivalent of an overengineered snow globe, us being an artifact nobody has noticed and that nobody would find particularly interesting if they did notice.
> Is light slow? Or is the human perception of time just scaled down as a result of our rapid metabolism and infinitesimality?
It's slow for humans to explore the cosmos.
"Slow" is meaningless without a frame of reference, and "humans" seems like a good frame of reference, since it's us -- and not plants or stars -- who are writing on HN to discuss this.
Because it's us, humans discussing this in HN, the frame of reference is implied and it's not necessary to spell it out.
That’s one of the answers to how you could go to the stars: go sloooooow as in slow down your cognition and metabolism so the trip doesn’t take long.
Ents could fly to the stars no problem.
Makes me wonder if there might not be a bunch of star faring “slow life” out there that we don’t notice for the same reason a hummingbird doesn’t notice trees growing.
It only seems incredibly slow in this model because it doesn't take special relativity into account. If it did, then as you approached the speed of light the Lorentz contraction would make wherever you are heading appear less far away. You can in theory get anywhere in the universe in an arbitrarily short amount of proper time your own reference frame. Of course, you might not survive the G-forces, but that's another matter.
Don't forget gravity drive. No more Gs. And the same technology would give us real artificial gravity, not this nauseous rotation artificial gravity.
The Lorentz factor at 0.5 c is 0.86 so this only reduces your proper travel time by about 15%. Even at 0.9c the LF is only 0.43, so it would still take you 2 years just to get to Proxima Centauri. And as you approach c, 1G acceleration speeds you less and less. And you also have to slow down at your destination.
> 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.
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.
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.
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.
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.
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
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.
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.
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.
10,000 years of empty space to get to the next solar system. Exciting.
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.
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.
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.
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.
If you travel at relativistic speeds, your trip will appear far shorter to you than to those that stayed on Earth.
With a ship able to accelerate at 1G continuously, you can be at the edge of the observable universe in <50 subjective years [1].
[1] https://www.reddit.com/r/dataisbeautiful/comments/s4tbry/oc_...
Not naive at all. With chemical rockets we can only sustain 1G for a few minutes, so it won't do at all for interstellar flights.
There is a known way to achieve 100% fuel efficiency: antimatter. By storing equal parts matter and antimatter, you can fuse them to propel your spacecraft. It's unknown wether or not this kind of engine can actually be made.
Alternatively, and even more far-fetched, you could onboard a small singularity. Dumping anything into it will result in it being turned to pure energy at 100% efficiency, through Hawking's radiations. The smallest the singularity, the fastest it radiates, meaning you can sort of control the output. You can create singularities with very large particle colliders.
With 100% fuel efficiency you can probably sustain 1G for long enough to reach the nearest stars. You would need a very large spacecraft (on the order of kilometers) for a comparatively very small payload. And it would arrive completely empty at its destination, meaning no turning back. I think I saw someone do the math, but can't find it anymore.
Anyway, there are other difficulties. Travelling at .99c means tiny space dust now becomes very dangerous. So does radiations, all made extremely energetic by the Doppler effect.
On the plus side, continous 1G means you have artifical gravity for the whole trip.
Amazingly, yes, in a few ways (the mechanics are possible). But no in as many ways. (Fuel, sustainability, tracking)
The greater barrier is that the nature of the expansion of the universe prevents any real interstellar travel that has a "destination" in mind. Of course we might have some "FTL" or "near light speed" travel in futre, but if the universe is expanding infintely from every point in space at light speed, how could we ever "catch up" to objects we see even now?
This is not true. Expansion does not affect gravitationally bound structures. Our galaxy, and even the other galaxies in our local cluster, will stay in reach.
Source: https://www.reddit.com/r/askscience/comments/sr7fuo/is_there...
If your travel involves the Rocket Equation the answer is no. If you are limited by the speed of light and the lifetime of human civilization then the expansion of the universe is not an issue. Traveling between nearby solar systems is very close to impossible, traveling between galaxies is outright impossible.
The lifetime of human civilization problem is an odd one, because due to relativity, one-way trips are not an unsurpassable hurdle ( 2-3 generations on a 1 G spacecraft to get pretty much anywhere). But you can't come back, because it's basically guaranteed there'll be nothing left for you to come back to. Because while it might take "only" two hundred years from the passengers perspective to reach the edge of the (current) observable universe and come back, they'll be arriving 90 billion years in the future.
Luckily FTL communication isn't actually impossible and special relativity only applies to energy and mass.
True but doesn’t matter how slow light is. The closest to c your speed is, the shortest the time you experience on board of the space ship. At light speed, space and time cease to exist. You reach destination instantly.
So the goal is to create engines that can take us close to light speed. Then the issue is braking (spacetime expands as you slow down…)
Stephen Baxter wrote a story named The Gravity Mine about the descendants of humanity living after all stars have died. They get energy from black holes but even they are starting to noticeably shrink. Their perception of time is billions of times slower than humans and the upshot of this is that the speed of light would actually seem pretty fast.
Depends on who you mean by we. The universe is weird and it's entirely possible for you or I to travel essentially arbitrarily far in a single human lifetime, easily billions of light years. Relativity doesn't simply work as a speed limit; instead when things approach velocities anywhere near the speed of light, the universe starts contorting itself in really weird ways to maintain the perceived consistency of the speed of light.
From the perspective of somebody in a ship moving at relativistic rates, distances would begin to physically contract, and time itself would begin to speed up relative to an at rest observer. Here [1] is a calculator to see what this all mathematically works out to. For instance, you could travel to Andromeda, some 2 million light years away, in about 28 years in a ship that was capable of sustaining acceleration at 1g for 28 years. Of course for everybody back home 2 million years would pass. So if we ever achieve ships capable of this sort of acceleration, life is going to get really weird and non-linear, so far as time is concerned.
And this isn't some just some weird fringe theoretical/mathematical thing. For instance GPS satellites have to compensate for time dilation because relativistic effects, though small in this case, would otherwise have a substantial effect. Another example is at things like the large hadron collider. As a convenient effect of relativistic effects, emergent unstable particles exist far longer than they 'normally' would before decaying due to the fact they're moving at relativistic rates.
In other words, this is all very real. The only questionable issue is whether we can discover some sort of an energy source capable of accelerating a ship at 1g for tens of years, and develop sufficient shielding for such a vessel. That's still very much in the domain of sci-fi, but simultaneously seems like something that one wouldn't be entirely surprised to see was discovered just a century from now. This was the most tantalizing possibility behind the EMDrive stuff. [2] Well that or infinite energy, but it seems that universe won't be broken quite so easily just yet.
[1] - http://www.convertalot.com/relativistic_star_ship_calculator...
All of fiction and discourse fails to consider that the Solar System is actually a huge place and just the period of settling and industrialising it will take hundreds of years.
Everyone things that a game breaker technology is better engines, or fusion, or FTL, but they are wrong, the game breaker technology has already happened: 3D printing.
If we can manufacture things with minimal infrastructure using local resources, we can that is all we need.
And all of it reachable with simple nuclear power and technology we have today.
Exactly, there is free fuel and aluminium just floating by, and we are unable to use them to upgrade our ships or refuel them.
Until we make full use of robotics and 3D printing, there is no point of heading far. And we have all the tools.
Distant stars will not be settled by a fast small ship travelling from earth. They will be settled by a city sized monolith produced by harvesting and smelting an entire small moon
> Distant stars will not be settled by a fast small ship travelling from earth. They will be settled by a city sized monolith produced by harvesting and smelting an entire small moon
I don’t even think you’d need a whole moon unless it was a tiny one. Nonetheless, by the time we send a ship to another star, building these kinds of large self-contained habitats will be old hat.
I believe the OP was referring to relativity - the closer to the speed of light you get the slower time appears to tick. So if you could travel at light speed you'd arrive at your destination immediately from your reference frame, but much slower from another person's.
Well, if you were traveling at light speed you could move anywhere in the universe instantly. If you are an observer on earth, watching an object move away from you at the speed of light, then it will take a very long time to traverse the tiniest regions of the universe.
Er, "instant" here is "relativistic instant."
even in a vaccum, light speed travel from the travelers POV still takes time, and said traveler would perceive time passing exactly as occurring in that local space. But yes you're totally correct, the observer on earth would in this time see only the briefest part of my journey's trail due to light from my journey taking "exponentially" longer to travel back to the observer.
Is light slow? Or is the human perception of time just scaled down as a result of our rapid metabolism and infinitesimality? People historically mistake plants for being inanimate things with no reactivity, that they are far more simple and stupid than they truly are. Outside of a few exotic examples, plants simply operate on a wider timescale that's basically imperceptible without careful and particular observation. It becomes much more apparent how alive plants are when we observe them in a time-lapse. Now realize that plants are still relatively short-lived. The absolute oldest ones only go back to the early neolithic, that's only 14000 years or so. 1000 years is a long time for humans, but probably not for the trees where a single one can live 10x that.
From the hypothetical perspective of a star, with a lifespan measured in billions upon billions of years, the entire ecoscape of the world changes in a blink. From the sun's perspective, MENA was green just a very short while ago. Hell, Pangea wasn't that long ago. At this timescale, continental drift would be as apparent as the movement of boats are to humans. Anything that's working at the cosmic scale where the seemingly low speed of light sounds exhausting is most definitely working at this stellar perspective at the minimum. 14000 years of travel might as well be the equivalent of a 10 minute commute to the store.
Philosophically speaking, of course.