Ask Ethan: Is Interstellar Travel Possible? (Synopsis)

"Oh, yes — I know you. There was a time you looked at the stars and dreamed of what might be." -Star Trek: Nemesis, spoken by Jean-Luc Picard

The stars call to us through the ages, with each and every one holding the promise of a future for humanity beyond Earth. For generations, this was a mere dream, as our technology allowed us to neither know what worlds might lie beyond our own Solar System or to reach beyond our planet. But time and development has changed both of those things significantly.

Image credit: NASA, 1981. A remote camera captures a close-up view of a Space Shuttle Main Engine during a test firing at the John C. Stennis Space Center in Hancock County, Mississippi. Image credit: NASA, 1981. A remote camera captures a close-up view of a Space Shuttle Main Engine during a test firing at the John C. Stennis Space Center in Hancock County, Mississippi.

Now, when we look to the stars, we know that potentially habitable worlds lurk throughout our galaxy, and our spaceflight capabilities can bring us there. But so far, it would only be a very long, lonely, one-way trip. This isn't necessarily going to be the case forever, though, as physically feasible technology could get humans to another star within a single lifetime, and potentially groundbreaking technology might make the journey almost instantaneous.

Image credit: NASA / Digital art by Les Bossinas (Cortez III Service Corp.), 1998. Image credit: NASA / Digital art by Les Bossinas (Cortez III Service Corp.), 1998.

Come read about the possibilities (as well as the improbabilities) on this week's Ask Ethan!

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Is it possible? Yes.

Can we do it today? No. But nothing was asked about when, so I have to ask, why the omission?

Sorry to rain on everyone's parade, but the interstellar medium at high speed is nasty. Not only is there intense cosmic ray radiation, but a spacecraft striking random hydrogen atoms at anything over about 0.5c creates more radiation. The level of magnetic shielding needed in that environment would wreak havoc on our biology. It is not just the iron in our blood, but even the water that makes up more than 60% of our bodies is magnetic.

Here is what happens when you put a frog in a static 10T magnetic field here on earth:

There are also neurological effects by being in intense magnetic fields. People who work on MRI machines often report vertigo, metallic tastes in their mouth, and hallucinations. A magnetic field strong enough to protect a human from a lethal dose of radiation over 0.5c might be enough to kill that same person.

It may be possible to build a probe to send to nearby stars, but as for people; make yourselves comfortable. We're not going anywhere any time soon.

Can't read the full article because Forbes expects me to turn on/off all sorts of things in my browser. Too bad.

We can shield against a magnetic field. The larger issue is rocks and stuff that are NOT magnetic, so they don't get deflected. Inter dimensional shortcuts (hyperdrive) are probably our best bet for a "star trek" universe that doesn't violate the laws of physics.

By currently_awake (not verified) on 02 Jan 2016 #permalink

Sorry to rain on your parade, have you ever seen what happened when you drop a human body from a 10 story building? It's not pretty, but people can fly, despite claims to the contrary.

You have pointed out the extreme limitations of our current technology, thank you very much, but that has nothing to do with what we can do tomorrow - people have always said you can't, until someone does.

I don't know why we wouldn't send AI instead and and then grow humans when we got there as needed.

By Bud Haven (not verified) on 03 Jan 2016 #permalink

@Frank #5

With flight there were plenty of examples in nature that it was possible. With faster than light travel there are none.

There are zero examples of anything traveling through space faster than c, and anything with rest mass can't even travel that fast. Warping space also doesn't work because if you warped it enough to join some other point then you've created an event horizon. While that is possible, the other side is also an inescapable event horizon. What you've done is essentially created 2 black holes at different points in space with a common singularity. The only way you're coming out the other side is as Hawking Radiation.

Unless quantum nonlocality is a real thing and the mechanism that facilitates it is exploitable, then faster than light transmission of information isn't happening.

For sub-lightspeed travel, there are a lot of fun options such as building a linear accelerator all the way around the moon. You can then accelerate your spacecraft to high velocity using massive moon-based power stations before flinging it off in the direction you want to explore, but people are too big, heavy, and fragile.

Can we conceivably send probes to nearby stars? Yes, and maybe even in your lifetime. Keeping in mind that within the next 50 years machines will be better than you at everything, are we going to send human astronauts to nearby stars ever? Not likely.

Did anyone look?

There were proofs that man would NEVER be able to fly. This turned out to be incorrect.

There were proofs that it would be impossible to go faster than the speed of sound. This turned out to be incorrect.

As for evidence FTL can happen, I point you toward the expansion rate of the universe, proving that things CAN go faster than lite: the distance between objects.

Personally, I believe such warp drive is a load of bollocks, but it's less a load of bollocks than your claims that it is impossible.

I think terraforming Mars is more realistic than trying to travel to other stars. Especially if someday it becomes possible to slowly change orbits of asteroids and comets to make them hit Mars in a controlled way, increasing its mass, water (maybe even change its orbit and bring it closer to Sun).

As for planets around other stars, I would be just happy if someday it becomes possible to take hi-res pictures of them (I don't know even if it is theoretically possible).

Thought provoking article Ethan, but I have to take exception to this statement:
"A trip like this would take hundreds of thousands of years to reach the nearest star system, and seems to be within reach."
I dont think this is within reach, and may never be. Could we really make a massively complicated system like a colony space craft that would have a snowball in hell's chance of working for 100 000 years? The Long Now project is trying to make a simple clock that will last for 10 000 years, tick every year and indicate each millenium. Tens of millions have been spent and they still arent there. For example all electronics are out - they simply can't last even a fraction of that time. The Long Now is going for massive and simple mechanical stuff that might just do it, but a space ship that could support a human colony independently for 100 000 years? Would it use electronics? It would have to obviously. If so would it carry a foundry capable of replacing every single electronic component on the ship? How complex would that be in itself? What about the replacement parts for the foundry? How would you make those? And how would you make the stuff to make that? And so on and so on. As the logistics chain spirals out you find you need a significant fraction of the industrial base of planet earth to be self-sufficient at high tech levels for 100 000 years. Just think of the massive required complexity - and fragility over a time scale of 100 000 years. This is actually less plausible than almost any of the other ideas in this article.

By Waterbergs (not verified) on 03 Jan 2016 #permalink

@10 Waterbags

100 000 years in reference frame of earth... less time for someone in a ship traveling i.e 0.3c

but still a long time non the less.. and most of your points stand for building something that last even 1000 years

By Sinisa Lazarek (not verified) on 03 Jan 2016 #permalink


Could we really make a massively complicated system like a colony space craft that would have a snowball in hell’s chance of working for 100 000 years?

If you're really planning a multi-thousand year journey, I think the strategic thing to do is to build the "ship" as an isolated colony, let it run "in place" for several hundred years, then strap engines on it and start your journey. After all, a couple hundred years will hardly make a difference on the time scales you're talking about, but it would give your engineers a lot of time to ensure the multi-generational kinks are ironed out and everyone else confidence that the system will work over the travel time.

I put 'ship' in scare quotes because for such a massive endeavor, one possibility would be to build a habitat in a planetoid and then figure out a way to propel it (we use gravity to boost the speed on our space probes; I don't see why we wouldn't do the same thing here. But we'd have to have some sort of engines for maneuvering/braking when we get to where we're going...though I suppose if our travelers are really confident, they could sling their colony on it's path as soon as they figure the environment is stable and then they build the braking engines during the journey. Because they've got lots of time).

sorry about the html tag fail.

The section on warp drive doesn't make mention of the proposed Albubierre drive, of which at last reading Harold White suggested the mass-energy requirement may be only about ~700kg, so long as the solution to the problem of 'exotic matter' and controlling the warp bubble from inside (among a great many other problems) are solvable. It may still be impossible (or very, very improbable) and likely requires a reconciliation between general relativity and quantum mechanics which heretofore has not been worked out. There are problems yet-to-be-solved, but at the very least it seems to me that there has been more accomplished in this field than the author suggests.

By Samuel J. Lawson (not verified) on 04 Jan 2016 #permalink

@10 Waterbags
Fleet of worlds!

One thing that everyone (movies, books etc..) neglects is slowing down/stopping. In most, if not all, sci-fi renditions it's almost immediate... but physics doesn't work that way :) This adds another problem for interstellar travel... imagine you started building speed.. and you reach some decent fraction of c ... slowing down again is a huge problem.. you will either be doing it all the way from half the trip length.. in which case you are burning fuel all the way just in reverse direction... or something has to give. Drop suddenly in speed by whatever means.. and you become one with the ship.. literally :)

By Sinisa Lazarek (not verified) on 04 Jan 2016 #permalink

@16: most 'realistic' sci-fi that I've read assumes the solution physicists worked out decades ago was the most efficient: accelerate for half the journey, flip the ship 180 degrees, then decelerate for the next half. This also solves the "how do we create artificial gravity to keep the earth life healthy" problem.

Incidentally Sinisa, constant 1g thrust with a turnaround at midpoint would be plenty fast enough to allow interstellar travel with trip times shorter than a few decades of subjective traveler time...IF we could somehow manage it. Here is a graphic showing where you can reach; pretty much anywhere in the milky way galaxy in under 50 subjective years (note the graphic shows round-trip times, so divide by two for one way journeys).

There maybe other ways to slow down a spaceship.
For example, I think creating a giant magnetic field bubble around the ship would slow it down because of magnetic field pushing against charged particles/ions flying around.

@19: whatever the mechanism used, no human-containing spaceship will be able to use a sustained, high-g deceleration because it will kill or injure the people inside. For an interstellar journey, you're not talking about decelerating for a few seconds so 6-8g is okay, you're talking about a deceleration that's going to last years. So you're probably limited to below 2g for crew health reasons anyway. 1g might not be the limit, but its in the ballpark. This estimate, of course, does not consider more exotic technologies like freezing people in a way where their bodies can withstand higher gs. If you can do that, yes you can use higher decelerations at the end of the journey (high accelerations at the beginning too...and I believe the most efficient solution to how to get there quickest is still the 50%/flip/50% one...).

Assume we have the means to attain an average velocity of 0.01c (1% of light speed). At that rate a star system 30 LY away is a 3,000-year trip: a 100-generation ark ship. (I'm using the term "ark ship" rather than "colony ship," since strictly speaking there won't be a "colony" that produces monetizable value for its parent entity.)

Question: what degree of relativistic time dilation will occur as a result of a trip at a max velocity somewhere in the range of .05c and mean average .01c? Will anything like answerable communication with Earth be possible?

An ark ship could be built from a large space rock hollowed out to build a habitat inside, of size sufficient to support a human population that won't get inbred. Alternately, scrape together enough gravel from the Kuiper belt, and stick it together chemically in a manner analogous to concrete. Another method might be to use fusion as a heat source to melt either source of rock into glass up to some reasonable depth. Either way, living on the inside of a rock sphere is good for reducing pesky cosmic rays, and the sphere could be rotated for artificial gravity during the turnaround phase of the trip.

Assume propulsion can be solved with something based on fusion or other methods within the scope of current physics. Longevity of the ark ship's internal habitat systems could be solved with an ark ship of sufficient size to accommodate all the needed tech including metal foundries, chip fabrication, etc.

To choose a destination: one-way trips of robotic probes using the chosen propulsion system. While the probes are on their way to candidate worlds, we have time to build a prototype ark ship and fly it in Solar orbit at a distance that enables giving its propulsion and habitat systems a decent workout. Temporary crews aboard that ark ship would fine-tune the technology and engineering until we had something that worked.

By the time we've chosen the destination from all of the findings of the robotic surveys, we've also got a habitat that's been tested to operate for thousands of years. Then we build another ark ship for the voyage, strap on the fusion motors, and we're off to the stars.

But by the time we're ready to send the first ark ship, it's a safe bet that there'll be new physics to consider, and new chemistry, materials science, and relevant technologies. Some of those will have gone through testing sufficient to be adopted into the ark ship that's going to make the voyage.

Between here and there we need: 1) Sustainability on Earth, to preserve a scientifically & technologically capable civilization. 2) Absence of global warfare for the same reason and to enable the surplus resources for humanity''s biggest engineering project. 3) Freedom of scientific and technological progress (subject to 1 and 2), and 4) Continuation of space exploration including colonies on the Moon and on Mars. In all likelihood, by the time we're ready to fly to another star system, there is a technologically capable human civilization on Mars, and colonies among the outer planets.

No need for cryo freezing of humans or 20-year-voyage miracle tech: those things only cater to emotional desires rather than to the long-term survival benefits of cosmic civilization. Cosmic civilization is not for "me" or even for "we," it's for our distant descendants. And absent some miracle tech, journeys to other stars will always be many-generational projects. Some of this touches on the definition of pure altruism, acts that have no benefit to self only benefit to others. Between here and the stars, we have some cultural evolving to do.


Denier @ 7: Quantum nonlocality / entanglement is a real thing, but per current physics, can't be used for communication. New physics might change that assessment in the future, but isn't to be counted on.

Anyone, re. habitat materials: Roman concrete has lasted 2,000 years and the structures are still standing. Roman concrete probably attained a maximum of 2,500 psi compressive strength; modern concrete can be produced as high as 10,000 psi, and it's likely that the 10K psi stuff will last as long as or longer than the Roman stuff. We won't be using concrete in the vacuum of space, but the point here is that the strength of materials isn't as big a problem as some of the other considerations such as building closed ecosystems and replacing electronics that fail due to aging.

Clearly a glassed-in rock the size of a small moon is a heck of a lot of mass to move, so that's going to be an issue. But it's a technology scaling issue rather than a raw science issue.

We can do this.

For today, what we need to focus on is sustainability, global peace, support for science in general, and support for an expanded space program. Those ingredients become the inexorable path to the stars.

Sinisa @ 22: Thanks!

I'm curious what sorts of evolutionary changes we might expect on the humans aboard a "generational ship" flying for hundreds of thousands of years. Any thoughts?

Not any more than you'd see here on earth over that time, and probably a lot less, since the environment will be pretty much constant and the ecology actually static.

Cosmic ray damage will not cause useful changes any more often than any other cancer-causing event. It happens too often and makes too much damage for selection to work on (and selection usually kills the aberrant cell(s) anyway, which could be bad if there's other stresses or just "not good" if everything is fine.

However, you'd be better off looking at biology for this. I don't know many biologists visit this blog.