Interstellar travel?

[TheMeInTeam]

We've yet to find anything that even plausibly allows for the ability to surpass lightspeed travel.

So that means our most realistic options known so far involve managing tech that allows us to push a healthy fraction of light speed plus the ability to extend or preserve life. We could also go the electronic minds route such that absent physical destruction you'd have consciousness indefinitely if you have energy.

We don't have the tech for any of this, but at unlike going FTL it's possible in principle based on physics we know.

FTL in any capacity would be a major game changer, but even indefinite or near-indefinite life coupled with something like .1c would allow some pretty heavy intra galaxy colonization. Makes you wonder about the Fermi paradox all over again.

 

[El_Machinae]

All my serious ideas would require some unlikely scientific breakthrough. An alcubierre drive would still require more energy than we can possibly produce or store. If we somehow manage to efficiently produce and stabiize antimatter we could get to one of our neighbouring systems even without FTL. Accelerate at about 1 g for about five years or so and you should be close to 50% c. Cruise at that speed for...I'm too lazy nor for proper math. Two years ? Flip the ship around at the half way point and then decelerate with about 1 g for the next five years.
If we only could create and store the needed fuel...

Time dilation is hilarious
http://convertalot.com/relativistic_star_ship_calculator.html
(bottom half of page)

After 5 years of acceleration, you're going about 0.98 c. A ten light year journey (with flipping over) takes 11 years, with a subjective time of 4.8 years.

 

[EgonSpengler]

Has anyone ever read The Forever War by Joe Haldeman? It's been a while since I read it, but it's about a sailor in Earth's interstellar navy, and because of time dilation at near-light speeds, his 2-year deployment in space translates to 20 years on Earth. Haldeman wrote it not long after returning from Vietnam, and it's always been viewed as a metaphor for readjustment disorders.

I've heard physicists talk about a Star Trek-style "warp drive" being maybe, theoretically, if you've had a couple of beers, more plausible than actual faster-than-light velocity. Something about how gravity wells (black holes being the most powerful, I guess) actually bend space. Still not even remotely possible, of course. I think the energy you would need is beyond comprehension.

 

[Hrothbern]

Nice calculator

At speeds near c, the energy you need is beyond the energy density per kilo of any fuel we have today and the impact of interstellar dust collision at near c will erode away the shields and the ship in no time at all.

And with that nice calculator
If we want to go to Gliese 832c at 16 light years, ignoring needed shields, and use 100% (!) enriched Uranium as fuel, being 80% of total weight once in space, we would reach max only 0.025 c, and need 1245 years to get there.
(acceleration taken at 0.00004 g, 100% Uranium taken at 83,140,000 MJ/Kg, assuming you need twice the energy shown in the calculator for max kinetic energy: to accelerate and to decelerate. A bit optimistic from ignoring the changed fuel-dead weight rate during the travel )

I guess we need anti-matter....

 

[red_elk]

Daedalus spaceship supposed to have fusion drive and reach Barnard's star in ~50 years.

 

[El_Machinae]

That's assuming you take all fuel with you. You could shoot out packets of fuel ahead of you, and then accelerate into them, for example.

You can shoot small packets faster, with less life support. Smaller mass means your solar sail plus lasers can get them growing faster etc .

Another point people miss about time dilation is that you never actually 'fall behind' on Earth. If you start watching the new GoT while in transit away, you can just keep watching uninterrupted. It's only communication that's impacted

 

[Lexicus]

I think I remember seeing some calculations to the effect that a ship the size of a trash can would need the mass-energy of Jupiter to travel across the solar system with an Alcubierre drive. Oh and the amount of energy is negative, whatever that means.

 

[red_elk]

I'm pretty sure building a spacecraft which would be able to reach nearby stars in several decades is possible even with our current technology level.
It would just take insane amount of time and money.

 

[El_Machinae]

I assume everone knows about the Breakthrough Starshot project. The billionaire wanting to send probes to Alpha Centauri in our life time

 

[Timsup2nothin]

I'm pretty sure building a spacecraft which would be able to reach nearby stars in several decades is possible even with our current technology level.
It would just take insane amount of time and money.

Hmmmmm. My not quite related experience makes me wonder about this.

I served on a submarine that was built before I was born. The hull was as solid as the day she was commissioned, but on any given day we could find ourselves bobbing around in the ocean getting the tub fixed so that we could go on about our business. But, it could bob around satisfactorily in the process, and we were there to fix it.

I came away with a monstrous distrust of airplanes. I don't believe they are really built with any better long term reliability than my boat was. So, knowing that they can't just bob around in the air while the crew fixes them up, I find the idea of relying on them to be more than I want to do.

So, shooting something into space for a decades long journey with "yeah, it's gonna be fine, even when it is thirty years old" is something I just can't get behind.

 

[uppi]

Oh and the amount of energy is negative, whatever that means.

That means you need to switch the sign of the energy in the equations so that the math works out. Nobody knows, whether that describes a physically possible state or is just math that is not related to reality at all.

In principle the energy is not zero, so by modifying the properties of the vacuum and removing energy (which is possible in small amounts), you could get negative energy. The problem is, nobody knows how big vacuum energy is in absolute terms, so it is unclear whether it would be possible to remove enough energy for a feasible Alcubierre drive. Quantum mechanics says there should be, astrophysics says there is not. Although I have more of a quantum mechanics background, I personally would put my money on the astrophysics side of the argument, which would mean a practical Alcubierre drive would be essentially impossible.

I assume everone knows about the Breakthrough Starshot project. The billionaire wanting to send probes to Alpha Centauri in our life time

Yeah, it is the most realistic proposal to get to Alpha Centauri I have ever heard, but it is still stretching the limits of realistic very far (at least the "in our lifetime" part, if you make it a 200 year project, it becomes much more realistic). It only works for microscopic probes and will only get you a flyby at very high speeds since there is no breaking involved. I don't think it will get you very far when you try to apply it to human space travel.

 

[red_elk]

About Breakthrough Starshot, I don't quite understand how these microscopic probes suppose to deliver the data back on Earth. Without sending information back, it will be as useful as hurling stones to Alpha Centauri.

 

[Timsup2nothin]

About Breakthrough Starshot, I don't quite understand how these microscopic probes suppose to deliver the data back on Earth. Without sending information back, it will be as useful as hurling stones to Alpha Centauri.

Well, if you did the flyby precisely right you could use stellar gravity to execute a screaming turn and get your stone to come back.

 

[Bootstoots]

My suspicion about the Fermi paradox is depressing for those of us who really do want to see interstellar travel or at least communication on a regular basis. It's that intelligent life is rare enough that it's uncommon for radio signals to be picked up between civilizations, especially during the fairly brief window where radio communication is loud enough to be picked up because of inefficient transmission.

But maybe intelligent life is not ultra-rare. The main barrier is that it never really makes any kind of economic sense to leave your star system and colonize anywhere else, or to send out von Neumann machines or anything like that. The distances are too vast, and it's rare to encounter a planet which is so similar to the home planet of a species that it can, or would want to, live on that other planet.

Just a hunch - I can't prove it. But I think it's quite likely that we just never will become a space-faring civilization, at least outside of the Solar System.

 

[Timsup2nothin]

Read Existence, by David Brin.

 

[El_Machinae]

Yeah, it is the most realistic proposal to get to Alpha Centauri I have ever heard, but it is still stretching the limits of realistic very far (at least the "in our lifetime" part, if you make it a 200 year project, it becomes much more realistic). It only works for microscopic probes and will only get you a flyby at very high speeds since there is no breaking involved. I don't think it will get you very far when you try to apply it to human space travel.

It's part of the momentum towards that eventual goal, though. That's the way I see it. I've always endorsed 'token' support towards developing our space technologies. A token amount, always affordable, but that amount grows with the economy so that successes can build upon themselves. It's why I try to spend $50 annually in that direction, to tokenly help create those compounding returns.

Just a hunch - I can't prove it. But I think it's quite likely that we just never will become a space-faring civilization, at least outside of the Solar System.

This posits that there is a cap to achievable wealth in our solar system, so that the Elon Musk of 3100 CE still doesn't have enough money to fund a sustainable expedition out.

 

[uppi]

About Breakthrough Starshot, I don't quite understand how these microscopic probes suppose to deliver the data back on Earth. Without sending information back, it will be as useful as hurling stones to Alpha Centauri.

The idea is that you have this giant reflective surface used to accelerate the probe and you could use that to direct a laser beam back at earth. Photon detectors can be made extremely sensitive, so as long as you manage to direct a few photons a second towards earth, there would be a detectable signal which could be used to transfer data. Of course this means that you need to cram a fairly good laser with good optics into the microscopic probe. I suppose with an on-chip laser and optics this could be done and I suspect that the controls required to point the whole thing back at earth might end up heavier than the optics system. Nevertheless, this somewhat hints at the problem with this proposal: It barely works if you put in the best numbers ever achieved for every component with little margin for suboptimal performance. Putting this all together in a tiny package without making any compromises would be one hell of an engineering challenge.

As I said above, if you make this a multi-century mission, you could make everything a bit bigger and heavier. With these relaxed conditions, the chance for success would be much higher. But then there would be the risk that if we wait 50 years, we might be able to engineer a probe that overtakes the multi-century mission, which would then be next to useless.

 

[Timsup2nothin]

Of course there's also the possibility that the data beamed back from a multi-century mission would be lost on the subsistence farmers struggling to stay alive in their post apocalyptic nightmare.

 

[uppi]

Of course there's also the possibility that the data beamed back from a multi-century mission would be lost on the subsistence farmers struggling to stay alive in their post apocalyptic nightmare.

By that time, they might have rebuilt civilization only to discover that some critical information to locate and decode the signal has been lost during the apocalypse.

 

[Cutlass]

I've thought on it a lot, and I feel that any successful mission to colonize another world has to start with 10s of 1000s of colonists on the first ship. This would, of course, be prohibitively expensive. So I don't see it happening.