The Q-Drive and the difficulty of interstellar exploration

I’ve discussed the difficulties of interstellar exploration before.  To get a spacecraft to another star within a human lifetime requires accelerating it to an appreciable percentage of c (the speed of light), say 10-20%.  In general that requires titanic amounts of energy.  (Forget about the common sci-fi scenarios of going into warp drive or jumping through or into hyperspace.  Those are fantasy plot devices with either no science or highly speculative science behind them.)

The mass ratio of fuel-propellant to the rest of the craft, using the most plausible short term option, nuclear pulse propulsion, is something like 10,000 to 1 to reach 10% of c, that is, for every kilogram of spacecraft you want to reach the destination, you’ll need 10,000 kilograms of fuel.  Although multiple stages would help, when we consider everything that would be required to send humans, things start to look pretty bleak.  It’s a little bit more hopeful with uncrewed probes.

One solution being considered is Breakthrough Starshot.  Use tiny probes with light sails attached, which are accelerated by ground based lasers to 20% of c.  The biggest issues with this plan include the cost and logistics of the ground based lasers, the challenges in successfully miniaturizing the craft, and the fact that there’s no way to slow the probes at the destination, so they’d have to collect what data they could during the few hours they had when flying through the destination system.  And their small size limits their transmitting power, meaning sending back the resulting data would require decades.

Another old solution proposed in 1960 by Robert Bussard, is to collect fuel from the interstellar medium.  The Bussard Ramjet (BR) has a tremendous electromagnetic scoop in front of it, which brings in the diffuse hydrogen floating ahead of the craft, compresses it so that it undergoes nuclear fusion, and expels it as propellant.  The idea is that the faster the craft is moving, the more fuel available to it, and the faster it can accelerate.  The biggest issues with the BR is that the interstellar medium has been found since Bussard’s proposal to be far thinner than he believed, and the drag of the scoop limits its overall effectiveness.

Alex Tolley has a post up at Centauri Dreams discussing a new proposal: the Q-Drive, as put forward by Jeff Greason, chairman of the Tau Zero Foundation.  Like the BR, the Q-Drive uses the interstellar medium, but in a different manner.  Unlike the BR, this craft uses an inert stored propellant: water.  (The water is stored as a giant cone of ice in front of the craft, acting as a shield against interstellar particles.)  The water is ionized and accelerated out the back of the craft, propelling it forward.

What comes from the interstellar medium is the power to accelerate the water.  This involves two large magnets that create a couple of magsails (sails made of magnetic fields), but instead of using them as sails, they function sort of like a wind turbine, in that they collect energy by slowing down (relative to the craft) the passing ionic interstellar matter, transferring the difference in kinetic energy to the drive.  The faster the craft is moving, the more energy collected, the faster it can accelerate the propellant, and the higher the thrust.

Tolley’s diagram of the Q-Drive interstellar craft. (Click through for source.)

Notably, the craft has to be initially accelerated to some small percentage of c by other means, such as the nuclear pulse propulsion I mentioned above.  But once that is achieved, that first stage can be jettisoned, allowing the Q-Drive to supposedly then reach speeds around 20% of c.  It can decelerate by pointing the drive in the direction of travel.  (It’s less clear to me how the final stages of deceleration near the destination would work.)

If you’re interested in the details, I recommend reading Tolley’s post.  Tolley is clear that this is something that seems possible in principle, but the practicalities may be another matter.  In particular, there is a question of whether the energy conversion can be efficient enough to make the Q-Drive more effective than just using something like the nuclear pulse rocket for the whole trip.

However, if it does work, or it can be developed into something that works, it may make interstellar exploration far more practical than it currently looks.

If you’re interested in the hard core technical details, check out Jeff Greason’s paper, or his talk on the subject.

Greason’s primary message in the talk is to emphasize the key idea, that drag energy from the surrounding medium (the interstellar medium in interstellar flight, the solar wind in solar system flight) represents an untapped energy source.

It’s been a while since I saw a new idea in this space.  Interstellar travel is a very hard engineering problem.  Hard enough that some scientists think it’s effectively impossible.  It’s nice to see someone make a possible dent in that problem.

The problems with ensuring humanity’s survival with space colonies

Artist impression of a Mars settlement with cu...
Artist impression of a Mars settlement with cutaway view (Photo credit: Wikipedia)

Stephen Hawking, as he has done before, expresses a common sentiment, that we need to colonize space in order to survive.

Humans should go and live in space within the next 1,000 years, or it will die out, Stephen Hawking has warned.

“We must continue to go into space for the future of humanity,” Mr Hawking said. “I don’t think we will survive another 1,000 years without escaping beyond our fragile planet.”

…In February, he said that humans should colonise other planets as “life insurance” for the species, and could be the only way of ensuring that humanity lives on.

My first reaction to this is that if we’re looking for space colonies to ensure the survival of the human race, we have a long way to go.  It seems to me that the first goal is simply to create a successful viable long term closed ecological system that can support humans.  As I understand it, every experiment attempting to do this so far has failed.  I think we need to succeed pretty strongly at that before attempting to do it in habitats millions of miles away, like on Mars.  Until we do, any space colony is going to be crucially dependent on a thin and fragile lifeline from Earth’s biosphere.

It’s also worth noting that, once we can create a closed ecological system, we might be better off creating colonies here on Earth.  A closed hardened underground habitat would be a lot easier to build and maintain and would probably do just as much to ensure humanity’s survival.

Anyone who thinks doing off world colonies is a substitute for fixing our environmental and social problems doesn’t understand the obstacles involved in any foreseeable colony.  Mars, the best candidate right now, is cold and desolate in a way that makes Antarctica look like The Garden of Eden.  Add no oxygen, very low air pressure, and we have an environment that humans can’t exist in without spacesuits.  Add radiation exposure from Mar’s lack of a magnetic field, that would force humans to stay underground most of the time, and the idea of consigning humans to live there for the rest of their lives starts to look a bit sadistic.

(None of this is to say that I think we shouldn’t have researchers and scientists on Mars, just as we currently do in Antarctica.  But no one is really tempted to colonize Antarctica.)

Looking at the longer term, people talk about things like terraforming.   But I strongly suspect that, by the time we have the technology and power to actually have a chance at terraforming an environment, we’re going to find that it’s a lot cheaper and easier to modify ourselves for the environment rather than the environment for us.  We will likely colonize other worlds, but doing so will probably force us to give up the evolved forms that are fine tuned for Earth’s biosphere and location.

At the end of the lecture, Hawking encouraged his audience to “look at up at the stars and not down at your feet”.

I’ve written before about the immense difficulties in any foreseeable interstellar travel.  In short, FTL (faster than light) travel, a common plot device in science fiction, would most likely require a new physics.  But before you let that bother you, consider that even getting to an appreciable percentage of the speed of light will require appalling amounts of energy.  (Think in terms of fuel equivalent to the mass of a planet possibly being necessary to accelerate a decent sized manned ship to, say, 10% of the speed of light.)

Our most likely path to the stars will be microscopic probes, with enough intelligence to bootstrap an infrastructure at the destination solar system using local resources, and to transmit their findings back to us.  It’s hard to see human interstellar travel being anything but the most extravagant of vanity projects, unless mind uploading of some type or another becomes possible.

Stephen Hawking has repeatedly warned of the danger that humanity finds itself in, as a result of the rise of artificial intelligence and the dangers of human aggression and barbarity.

I’ve written repeatedly about why I think the dangers of AI, although real to some degree, are vastly overblown.  I won’t reopen that debate here.  The only thing I’ll point out is that if AIs are a danger on Earth, they’d also be a danger in a space colony, or anywhere else we’d go and be tempted to use them.

On the dangers of human aggression and barbarity, if we did solve the problems of closed ecosystems and had colonies around the solar system, and humanity reached a point where it destroyed Earth’s biosphere in a war, it’s not clear to me why such a war would stop there.  It’s extremely difficult to protect yourself from a space based attack.  The attacker can always go further out to accelerate an asteroid or something similar at you, allowing kinetic energy to wrought destruction.  Space colonies might slightly increase the probability that humanity survives such a war, but not nearly as much as people like to think.

None of this is to say that I think humans shouldn’t colonize space, in the long term.  But thinking that we are doing it to preserve the species is misguided, except in the very broadest of terms and time scales.  (Think human intelligence, in one form or another, surviving the evolution and eventual death of the Sun.)

In the mean time, our best chance of survival, it seems to me, is to address the real issues we have here, because we’re a lot more likely to destroy ourselves than to have nature do it to us.  The threats of nuclear war or terrorism, global warming, biological warfare, or overall overpopulation, worry me a lot more than a species ending asteroid strike or other mass extinction event, which only happens once every 50-100 million years.  (Not that we shouldn’t do what we can to protect against asteroid strikes.  Even one that doesn’t endanger the whole world can cause a lot of devastation.)

I think the best way to protect against the threats of us destroying ourselves, indeed the only way over the long term, is to give as much of humanity as possible a stake in the success of human civilization.  This involves fighting poverty worldwide, and promoting women’s rights, which will help with the population problem, which in turn helps with just about every other problem.

If we really want to maximize humanity’s long term survivability, that’s where we should start.  The good news is that, when viewed through the broad sweep of history, things are moving in the right direction.  The only question is whether that movement will be fast enough.

Greg Egan’s Amalgam is close to the most likely interstellar civilization

The other day, I did a post engaging in speculation on, assuming we don’t discover a completely new physics, what I thought an interstellar civilization might look like.  In summary:

  1. Given special relativity, travel faster than the speed of light is impossible.  This has been verified by innumerable experiments, and nothing in nature has been observed to travel faster than light, at least not yet.  There are various notions of ways around this (wormholes, Alcubierre drives, etc) but they are very speculative, requiring the existence of either exotic or cosmological amounts of energy.
  2. Even getting a decent sized spaceship to an appreciable percentage of the speed of light requires appalling amounts of energy.  This has led some scientists to conclude that humans will never explore beyond the solar system.
  3. Sending a small probe (possibly microscopic) is still extremely expensive, but conceivable.
  4. A fleet of small probes could be sent to other stars.  Once there, they could find local raw resources and bootstrap a communication and exploration infrastructure.
  5. These probes could even manufacture copies of themselves to be sent to stars further out.
  6. Over time, an interstellar communications network could be developed, allowing information from throughout the galaxy to be transmitted back to Earth, and AI (artificial intelligence) entities could be sent to the stars to explore.
  7. If mind uploading of some form or another is possible, human minds could be sent to the stars.  If mind uploading is not possible, humanity may have to content itself with the information it receives from its interstellar network.

Wyrd Smythe pointed out to me that this was more or less the vision that Greg Egan has with his Amalgam stories.  Egan is a science fiction author who has explored the concept of mind uploading extensively in his fiction, perhaps more than anyone else so far.  I’d read some of Egan’s work before, but had missed the Amalgam ones.  The Amalgam is the name of the interstellar civilization in the stories.

The Amalgam is introduced in the short story, ‘Riding the Crocodile’, which is available for free on Egan’s web site.  Egan calls the self replicating probes “spores”, which I think is a pretty descriptive label.  He describes the operation of the spores in the opening pages of another story, ‘Glory’, which is also available for free.  If the idea of this type of civilization interests you, I highly recommend both stories.  (I actually had read ‘Glory’ some years ago, but hadn’t realized the Amalgam background to it.)

IncandescenceCoverIf you find yourself with a burning desire to know more about the Aloof, the mysterious alien network in ‘Riding the Crocodile’, then you can read Egan’s novel, ‘Incandescence‘, which gives insights into them.  I should warn you that, while I mostly enjoyed ‘Incandescence’, particularly all of the fascinating ideas that it explores, I often found it tedious.  Most of the novel is about aliens working out the principles of general relativity, which it describes in what I found at times to be excessive detail.  (Egan’s stated attitude is that it’s okay for a fictional book to require you to take notes to keep up.  Not sure how many readers will agree.  I didn’t take notes, but can’t say I always kept up either.)

Egan gives insights into the Aloof, but only indirectly.  The reader has to piece them together from the clues left by the two plot threads.  Many readers finish the book in a state of confusion.  If you do read the book, and find yourself in that state, at least with regards to the Aloof, my recommendation would be to read the opening pages again, up to the point where the Aloof is described, then reread the final page.

While I think Egan’s Amalgam concept has a lot going for it, there are a couple of things about it that I find a bit dubious.  The first is that the society described is very utopic.  Everyone in the Amalgam just gets along with everyone else.  Don’t get me wrong, I’d love to live in such a society.  It follows a common vision in science fiction, of the post-scarcity civilization.  While it’s nice to hope for that, I’m not sure how realistic it is.  Even if your resources span the galaxy, there will still only be so much of those resources, which means economy and conflict will likely still be facts of life.

The other is that the Amalgam is an conglomeration formed from multiple alien species.  I’ve given my reasons why I think that’s unlikely.  Egan does leave room for the possibility that some or all of those other species are “uplifted” ones, species whose intelligence has been boosted by other intelligent species, which I think is more plausible.

Egan’s vision is the closest I’ve seen in science fiction to what I think is the most realistic vision of humanity reaching the stars.  Of course, even the most educated guesses of what reaching the stars will look like is probably as far off as a 15th century monk’s speculation on how humans might reach the moon.  But the Amalgam strikes me as more likely than the common Star Trek like visions.  (Not that I’m not a fan of Star Trek.)

Three conditions are necessary for SETI to succeed

The Parkes 64 metre radio telescope at the Par...
(Photo credit: Wikipedia)

Tom Hartsfield has a post up at Real Clear Science criticizing both the Drake equation and SETI:

If you like science fiction, you’re probably familiar with the Drake equation. This famous one-line formula solves for the number of intelligent alien civilizations within our galaxy with whom we might be able to communicate. Supporters of the search for extraterrestrial life (SETI) often refer to the expression to bolster their case.

There’s just one BIG problem with the Drake equation. It’s completely useless! In fact, I believe it may actually misrepresent the search for ET and limit our ideas about it.

Hartsfield goes on the discuss the impossibility (at least currently) of knowing the values for each of the variables.  Because of this inability to test or observe the various values, he says, the formula is non-scientific.

He then takes aim at SETI (the search for extraterrestrial intelligence):

The worst thing about the Drake equation is that it gives us a false idea of grasping the problem we are trying to solve. A mathematical equation connotes some scientific study or understanding of a subject. But this is misleading: SETI is simply NOT a scientific endeavor. It’s entirely a leap of faith, albeit a leap that uses tools devised by science. It’s like searching for paranormal activity with an electronic sound recorder.

Now, I happen to think that, due to the Fermi Paradox (if there are thousands of civilizations out there, why aren’t any of them here?), the probability of large numbers of civilizations within our galaxy is pretty small.  That doesn’t mean there aren’t civilizations in other galaxies, but they may be hundreds of millions of light years away.

That being said, I think Hartsfield is being overly harsh in his assessment.  The Drake equation has never been meant to be anything other than a stimulus for discussion.  Most people who understand this subject know that it’s essentially just structuring our ignorance.  Given its original goal, and given that people still talk about it today, I think it is fairly successful.

Is it scientific?  That depends on your definition of science, but I think the variables are things humanity may be able to measure, someday.  A scientific theory doesn’t have to be testable immediately in order to be considered science; it just needs to be testable in principle.  I don’t know too many people who would actually call the Drake equation a theory, but to what extent it’s modelling the problem might eventually be testable, at some point in the future.  I think everyone acknowledges that the Drake equation is almost certainly incomplete, in that there are probably numerous factors that influence the final number that we’re simply not aware of yet, but that applies to many things in science.

I think calling SETI unscientific is simply engaging in polemics.  SETI is definitely a long shot.  But the search is being conducted carefully and empirically.  Saying that the people who are going about it aren’t being scientific, comparing them to paranormal investigators and the like, is just making a value judgment about their enterprise while pretending to be objective.

Now, as I said, I do think SETI is a long shot.  There are certain things that have to be true for it to work.

  1. There needs to be a large number of civilizations out there.  Enough that a number of them are close enough for us to detect them.
  2. Pervasive interstellar travel needs to be impossible, or so monstrously difficult that hardly anyone bothers.  Otherwise they would have been here long ago.  Even if only 1% of light speed is achievable, that’s still fast enough for a fleet of self replicating probes to colonize the galaxy in 100 million years.   (No, there’s no evidence that they’ve been here, despite what the Ancient Aliens people say.)
  3. They need to communicate in a manner that is detectable with our current technology.  If there are civilizations out there, they may be advanced in ways we can’t fathom, and us attempting to listen in on them may be far more fruitless than a primitive hunter-gatherer tribe attempting to listen in on global communications, by watching for smoke signals.

It seems to me that these three constraints make success for SETI unlikely, but not impossible.  And nothing about how unlikely it is to be successful necessarily makes it unscientific.

Personally, given 2 above, one strategy to find extraterrestrial intelligence may be to search for probes in the solar system.  It may be that there are several already here, laying low.  Of course, if they are here and dormant, you have to wonder what they’re waiting for, how far advanced the civilization on the third planet is going to have to be before they initiate contact.  And given the vastness of the solar system, if they don’t want to be detected, the chance of us being able to do so seems remote.

A close pass by a red dwarf star, and a note on interplanetary and interstellar distances

First, in case you haven’t heard: 70,000 Years Ago, Another Star Flew by the Edge of the Solar System | RealClearScience.

According to an international team of astronomers, about 70,000 years ago a red dwarf star — nicknamed “Scholz’s star” for the astronomer who discovered it — passed by our solar system just 0.8 light years distant. In fact, 98% of the 10,000 simulations the team ran projected that the star’s path grazed the outer edges of the Oort Cloud, a region of space filled with icy planetesimals which marks the final boundary of our solar system.

…Scholz’s star is now twenty light years away and won’t be returning anytime soon. However, Dr. Coryn Bailer-Jones of the Max Planck Institute for Astronomy calculates that we may receive another visitor in the distant future. Last December, Baller-Jones reported that the rogue star HIP 85605 may pass as close as .132 light years to the solar system between 240,000 and 470,000 years from now. That’s a close miss on the cosmic scale, but more than far enough that our futuristic ancestors will have little to worry about. The only concern would be that HIP 85605’s foray through the inner Oort Cloud might send a few comets careening in Earth’s direction.

This is interesting and just goes to show that, on a large enough time scale, assuming we don’t drive ourselves extinct, humanity will eventually be able to go to the stars, even if we have to wait for other stars to occasionally come near us.  (Not that we could make such a trip with current technology, but it’s a lot easier than reaching the nearest current star.)

That said, it’s important to keep in mind what “near” means in this context since some news outlets are saying the star passed “within” our solar system, implying to most people that it passed near the planets or something.  As Pomeroy notes, this pass was 0.8 light years away.  While it’s less than a fifth the distance to the current nearest star (Proxima Centauri), that’s still over seven trillion kilometers, over 52,000 times the distance between the Earth and the Sun, or more than 1300 times the distance to Pluto.  Even the star HIP 85605 mentioned above that might some day pass as close as 0.132 light years away will still be more than 200 times the distance of Pluto.

Saying that these near passes are within our solar system is only accurate if your consider the solar system to encompass the theoretical Oort Cloud, thought to be a cloud of icy rocks that extends as far as 2 light years away, or half the distance to the next nearest star.  While some might argue that the phrase is accurate, it’s a far broader meaning of “solar system” than most people are familiar with.

It also illustrates that, as large as the solar system is, and it is incomprehensibly large by any human scales, it’s essentially the outer layers of the Sun when seen from interstellar distances.

Space is big. Really big. You just won’t believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it’s a long way down the road to the chemist’s, but that’s just peanuts to space.

Douglas Adams, The Hitchhiker’s Guide to the Galaxy


Eavesdropping on E.T. and the possibility of interstellar travel

Gabriel Popkin as an article at Inside Science about a study that looks at the possibility of intercepting communications between other alien civilizations.  The idea is that communicating across interstellar distances is best done with lasers.

So far, the optical search for extraterrestrial intelligence has focused mainly on the hope of receiving—and recognizing—an intentional, laser-encoded message. Researchers use dedicated telescopes or mine astronomical data collected for other purposes, like the Sloan Digital Sky Survey, to search for light pulses that could not be produced by any known object like a star. So far, no one has reported a light pattern that suggests an extraterrestrial intelligence.

But rather than look for light beamed directly at us, astronomers could also try to intercept signals sent between two distant civilizations. If advanced beings have existed for millions of years, they may well have found each other and started talking. Eventually many light beams would penetrate the intergalactic darkness, creating a criss-crossing network of communication beacons. As our solar system revolves around the galactic center, could we meander into the path of one of these beams?

While an interesting idea, the study largely concluded that this is unlikely to happen.

Unsurprisingly, he found that the chance of intercepting another civilization’s messages increased as more civilizations joined the communications network. He also found that the interception probability increased dramatically as the angle through which the beams spread out increased.

But the probability of accidentally wandering through a beam remained small as long as the beams were narrow, or collimated, like a typical laser. The beams would have to spread out about 1,000 times more widely than a standard laser pointer—in other words, more like a flashlight beam—before we have a decent chance of intercepting them, Forgan says. Sending out such a wide beam would require far more energy than emitting a tightly collimated one.

This isn’t too surprising.  Interstellar space is vast, and solar systems are (relatively) tiny.  As the article discusses, the aliens would have to go expensively out of their way to increase the odds of being detected by a third party.

One thing I find interesting about these studies, is that they have an implicit assumption: that interstellar travel or exploration is impossible, even robotically.  Because if it is possible and there are indeed hundreds of civilizations in the galaxy, then there would likely already be a communication relay in every solar system, and a vast interstellar communication web network.  If so, then our system would almost certainly have multiple beams interacting with other nearby stars.

If the aliens don’t want to be detected, it is possible that they could keep their relay stations in the Oort cloud, the region of comets and other icy bodies extending for a couple of light years out from the sun.  Of course, avoiding detection would have to be a major priority for them to keep their facilities so far away from the free solar energy of the sun.  But they could have decided to do so as soon as they noticed a tool using species developing on the third planet.  And if staying  hidden is a priority, we’re unlikely to find them for a while.

But, is the assumption that interstellar travel is impossible a valid one?  Or are SETI and other astronomers being overly pessimistic?  Most people are aware of the speed of light limitation, that nothing can travel faster than light.  But lamenting that issue is actually a bit of sour grapes, since we don’t even have the foreseeable technology to get to a significant percentage of the speed of light.  Just getting to 10% of c (the speed of light) will require astounding amounts of energy.

But it’s hard to imagine that in the centuries and millennia ahead, that we won’t be able to cobble together some method of getting to at least 1% of c.  There have been designs around for decades, such as the Orion Project, which would use nuclear explosions to propel a craft up to a high speed.  And there are many more speculative designs out there that could conceivably improve on that.

The problem is that Orion would still take centuries to reach the nearest star.  It’s easy enough for science fiction writers to wave their hands and imagine robotic probe machinery working that long, but engineering it is a different matter.  Still, Voyager 1 is four decades out and is expected to work at least another decade, albeit in a very low power mode.  Building a probe that could work for centuries would be difficult, but it remains an engineering challenge, not a fundamental limitation of physics.

And I think that’s why I remain optimistic that interstellar exploration will ultimately be possible, at least with robots.  Because the issues to be overcome are engineering ones, not fundamental scientific ones.  It’s hard to say whether those engineering challenges will be overcome in a century, a millennia, or farther out, but insisting that they never will seems unnecessarily pessimistic.

But as soon as we reach that conclusion, we’re back to wondering where everyone is (the Fermi Paradox).  Either they (or more likely their robotic representatives) are already here in the solar system, and hiding, as described above or in some other way, or they’re simply not there.  Or perhaps more accurately, the nearest neighboring civilization is millions of light years away in another galaxy, far enough away that they haven’t had time to reach us yet, if they ever will.

I would draw a similar graph for FTL and knowledge of physics

Click through for full sized version and the red button caption.

via Saturday Morning Breakfast Cereal.

Sometimes, learning science means discovering the constraints reality puts on us, and that part isn’t always fun.

The movie ‘Interstellar’ and wormholes

The other day, I did a post on interstellar exploration which linked to one by Sten Odenwald on the problems with interstellar travel.  Well, he posted some follow-up remarks, expressing some surprise at the response, doubling down on the aspects of the limitations of interstellar travel he identified, and urging people to be optimistically realistic.  (I predict he’ll get a similar response to this post.)

One thing I wanted to add to the remarks I made in my post, is that I don’t oppose research into possible faster than light solutions.  I just think we have to realistic about their prospects.  This subject is coming up again with the release of the movie ‘Interstellar’ tomorrow.

It sounds like a big part of the movie’s plot is going to involve wormholes.  These are actually theoretical concepts, and the movie had a heavy weight physicist, Kip Thorne, consulting to make sure they got it right.  (Thorne is actually releasing a book about the physics of the movie.)

As I said in my earlier post, these faster than light concepts are extremely speculative.  To understand how speculative, you might be interested in this write up by Paul Halpern at the Starts With A Bang blog.  The TL;DR is that traversable wormholes require something called “exotic matter” to produce “negative energy” to keep them from instantly collapsing.  Exotic matter has not yet been observed in nature.  Of course, that doesn’t mean it doesn’t exist, or that it couldn’t conceivably be manufactured.

But then there’s this:

Even if exotic matter is identified and put to use, there is another obstacle to traversable wormhole construction — the enormous amount of ordinary matter required. Researchers estimate that one would need a glob of mass comparable to millions of suns. Clearly, wormhole construction is not in the cards for the foreseeable future.

It’s always possible someone will find a way around these difficulties.  We don’t know what science will discover in centuries to come.

But if we’re doing scientific speculation, the probabilities are that exploring the stars will happen on far longer time frames than we’re used to now, and our best bet may be engineering ourselves to cope with those time frames.  Far out?  Sure.  But anywhere near as far out as harnessing the mass of a million suns to create a wormhole?

Reaching the stars will require serious out-of-the-box thinking

Sten Odenwald, an astronomer with the National Institute of Aerospace, has an article up at HuffPost that many will find disheartening: The Dismal Future of Interstellar Travel | Dr. Sten Odenwald.

I have been an avid science fiction reader all my life, but as an astronomer for over half my life, the essential paradox of my fantasy world can no longer be maintained. Basically, science tells us that traveling fast enough to make interstellar travel possible requires more money than society will ever be able to invest in the attempt.

Einstein’s theory of special relativity works phenomenally well, with no obvious errors in the domain relevant to space travel. His more comprehensive theory of general relativity also works exceptionally well and offers no workable opportunity to “warp” space in a way that can be technologically applied to space travel without killing the traveler or incinerating the universe. Interstellar travel will be constrained by the reality of special relativity and general relativity, and there is no monkeying with Mother Nature to make science fiction a reality.

…Andreas Hein, an engineer with the Icarus Interstellar Project, developed a rigorous method for forecasting the economics of interstellar travel, only to find that most economically plausible scenarios for a “Daedalus-type” mission would cost upwards of $174 trillion and require nearly 40 years of development and 0.4 percent of the world GDP. This would be for an unmanned, 50-year journey to Barnard’s Star using “fusion drive” technology. It consists of 50,000 tons of fuel and 500 tons of scientific equipment. Top speed: 12 percent of the speed of light.

There’s a fair amount of chest thumping in the comments decrying Odenwald’s pessimism, comparing him to people in history who claimed we’d never fly, exceed the sound barrier, etc.  Most of these commenters don’t understand how fundamentally different the challenges of interstellar travel really are.  Many of the historical thresholds they reference were engineering challenges, but there was never any serious doubt among scientists that they were fundamentally possible.

The speed of light limit is based on Einstein’s theory of special relativity.  It basically says that nothing with mass can reach the speed of light, much less exceed it.  The reason is that as your speed increases, so does your mass, albeit infinitesimally at normal speeds.  As you get closer to the speed of light, more and more of the energy you’re using to increase your speed actually goes into increasing your mass.  At 99.9999% of the speed of light, almost all of the energy goes to increasing mass.  To actually reach the speed of light would require an infinite amount of energy.  All the energy in the observable universe wouldn’t be enough to push a single proton up to the speed of light.

To be clear, nothing in nature has been observed to travel faster than light.  Lots of people have tried to find loopholes in the laws of physics.  They have speculated about things like wormholes, Alcubierre drives, quantum entanglement communication, and many other notions.  But these are all profoundly speculative concepts with zero evidence and major theoretical problems.  Many people know about some of the proposed solutions to these problems, but the solutions themselves are also profoundly speculative.  The majority of physicists are far from optimistic that there is any feasible way to travel, or even communicate, faster than light.

Even achieving a reasonable percentage of the speed of light is going to require major breakthroughs in physics if we want to send biological humans.  It’s trivial to espouse confidence that those breakthroughs will come, but counting on them is simply engaging in fantasy rather than scientific speculation.

Paul Gilster at Centauri Dreams, a blog I enthusiastically recommend for anyone interested in interstellar travel, has provided a couple of much more intelligent responses, here and here.  Gilster’s best argument against the economics issue that Odenwald raises is to point out how much of a difference centuries of economic growth might make, which I think is an excellent point.  But it only gets us to robotic missions, with manned missions being orders of magnitude more complicated.  And although his attitude is far more optimistic, his actual final conclusions really aren’t that different from Odenwald’s.

So, can humanity make it to the stars?  I think the answer is yes, but it’s going to require profound out-of-the-box thinking.  Forget Star Wars or Star Trek type universes unless you just want to fantasize.  We need to look at possibilities actually allowed by the laws of physics.  No one alive today really knows what interstellar exploration will look like.  But here is plausible speculation that doesn’t violate the laws of physics and recognizes that economic limitations would be important.

  1. Biological humans will likely never go to the stars, or if they do, it will be as symbolic vanity projects of a society orders of magnitude richer than we are today, and they will be going places pioneered long before by robots.
  2. Interstellar probes will likely be small, possibly microscopic, in order to economically be accelerated to a significant percentage of the speed of light.  Even launching these small probes will be staggeringly expensive, but there will only need to be one per destination.  (Or possibly two in case one malfunctions.)
  3. Once at a destination, the probe may be programmed to find resources (asteroids, etc) and bootstrap an infrastructure in order to communicate with home, to create local probes to explore the destination solar system, and possibly to create daughter probes to be sent on to farther stars.
  4. Once a communication link is established with home, information on the destination can be transmitted back.  Depending on the initial communications, new AIs might be transmitted to the destination to enhance the exploration.
  5. As speculated by Odenwald, biological humans will be able to experience the remote locations in virtual reality built using the information transmitted back.
  6. Is there any hope of humans ever routinely going to the stars in person?  Well, that depends on what we mean by “in person”, and our attitude toward the possibility of mind uploading, the plausibility some of us have been debating on another thread.  In the absence of that, it’s hard to see humans having much of a presence in other solar systems.

Learning to work in the universe we have, rather than the one we wished we had, isn’t always easy.  But once you get used to it, the possibilities are exciting.  Odenwald talked about how much more democratic the experience of these locations would be with all of us essentially doing it in virtual, rather than a select few elite explorers.  There’s a lot to like in that vision.

The future will be strange.  No doubt it will be stranger than we can imagine.  I’m convinced interstellar exploration can happen, but it will likely require us giving up preconceived notions of how we wish it could work.

Interstellar travel: Raising children in space

BBC Future has an article looking at how living in space might effect humans and society, and asking, among other things, should we have babies in space?

“Mars,” sang Sir Elton John in Rocket Man, “ain’t the kind of place to raise your kids.”

Sir Elton might be lacking in Nasa-related experience, but he had a point. Not only is the planet “cold as hell”, it is also isolated, airless and barren. Even the desolate view of rusty soil, lifeless valleys and bare mountains is shrouded in a permanent orange haze.

Nevertheless, it appears to be humanity’s goal to end up there. If all goes to plan, eventually – quite possibly within the next 50 years – colonists will be living on Mars. In the coming centuries, humans might also be packed onto nuclear-powered starships heading, over generations, for the nearest habitable planet. These pioneers – pilgrims if you like – will be starting new lives beyond Earth.

For these human civilisations to succeed, the space farers will need to start families. “If we’re going to have a long-term future in space, it won’t be done by a handful of astronauts, it’ll be whole communities,” says Cameron Smith, an anthropologist at Portland State University in Oregon.“It’ll have to be.” But can this work in reality?

via BBC – Future – Interstellar travel: Raising children in space.

The more I think about this, the less I feel that humans, in our natural form, will ever colonize other solar systems.  It’s all very well to talk about building generation ships, but if you think about what it would actually involve, it becomes pretty problematic.

First, there’s the issue of maintaining a self sustaining mini-biosphere for decades or centuries.  It’s easy to write about doing that, and many science fiction stories do, but we really have no clue yet how to make that work.  And if any aspect of the ecology of such a habitat goes wrong, there would be no recourse, no resupply shipments from Earth.  A generation ship would be completely on its own.  Of course we could imagine a fleet of ships, but such a fleet would still need to be a self sustaining ecosystem.

Power for the habitat would also be an issue.  Most of the energy in our solar system comes from the sun.  But there’s no solar power light years away from any sun, no fossil fuels, no renewable energy.  The ship would either need to bring all the power resources it would need for the entire trip (probably nuclear or fusion fuel), or maybe have it beamed in from an huge laser back home, which would provide decreasing power as the distances pile up.

The population of the ship (it’s not really accurate to call them a crew) would be constantly exposed to radiation.  We can talk about shielding, and that might be possible, but it will add more mass to the ship, which will increase the propulsion energy requirements, which for any conceivable interstellar trip are already appalling.

Speaking of mass, the minimum population for such a trip would need to be in the tens of thousands in order to insure a healthy genetic diversity both during the trip and at the destination, adding even more to the mass, habitat, and other requirements.

Now, I don’t doubt that human ingenuity might eventually find a way through all these issues.  But would our civilization consider it worth the cost?  Particularly with how much cheaper it is to send robotic probes?

As machine intelligence continues to increase, it’s easy to see how AIs would eventually be able to manage all the details of the trip, without mini-biospheres, radiation shielding, or minimum population.  It seems to me that, if we’re lucky, we might eventually be able to upload our minds into robotic probes, or transmit ourselves to colonies established by robots.  If we’re not lucky, the stars may belong to our machine progeny.

Of course, if someone manages to invent a warp drive, then all of this becomes moot.