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Saving Our World–Chapter Twenty-Eight–Is Interstellar Travel Possible?

Listen folks, I love a good sci-fi movie as much as anyone. Cruising around the galaxy, finding weird stuff, and blowing up aliens–it’s all good. But just because a writer can come up with something, it doesn’t make it possible. I’m sorry to say that we’re going to be bound to our solar system for a really, really long time. As in, probably forever.

Interstellar space travel is the fantasy of every five-year-old kid within us. It is the staple of science fiction serials. Boldly going where nobody has gone before in a really fantastic way. As we grow ever more advanced with our rockets and space probes, the question arises: could we ever hope to colonize the stars? Or, barring that far-flung dream, can we at least send space probes to alien planets, letting them tell us what they see?

The truth is that interstellar travel and exploration is technically possible. There’s no law of physics that outright forbids it. But that doesn’t necessarily make it easy, and it certainly doesn’t mean we’ll achieve it in our lifetimes, let alone this century. Interstellar space travel is a real pain in the neck.

Let’s get some perspective. The nearest star to Earth (which is also home to a small rocky world!) is Proxima Centauri, which sits a little less than 4 light-years away. Four. That’s doesn’t sound like a lot, does it? Imagine making a scale model of our solar system. Let’s say in that scale model you put the Earth three feet away from the Sun. In that scale model, Proxima Centauri would sit about 200 miles away.

It took one of our fastest spacecraft, New Horizons, traveling 36,000 miles per hour nearly a decade just to reach Pluto. If it were pointed at Proxima Centuari (and it’s not), cruising at that speed it would get to visit our nearest neighbor in about 25,000 years.

That’s a long trip.

If you want to visit another star system in any reasonable amount of time, you need to go fast. To go fast, you need a lot of energy. And that’s what makes interstellar travel so dang hard.

One proposed for an interstellar spacecraft is called the Starshot Initiative, which aims to shoot a super-powerful laser on a lightsail (a giant nearly perfectly reflecting membrane), using the energy from the light to propel the spacecraft to a tenth the speed of light. That would enable it to reach Proxima in less than half a century.

To make this work, the laser would have to use all the energy from every single nuclear reactor in the United States at once. And it would have to operate for 10 minutes, which is about a quadrillion times longer than we’ve ever operated our most powerful lasers).

Oh, right, and the spacecraft could weigh no more than a paperclip.

 

Nothing about the Starshot is physically impossible. Just really, really difficult and expensive…and using technology that is decades, if not centuries, away from coming to fruition (assuming we even want to develop that kind of technology in the first place).

Sure, there are more fanciful ideas out there, like building wormholes or warp drives. And while those concepts do have their roots in legit physics (most notably, general relativity, our modern understanding of the force of gravity), the reality of their near impossibility is also rooted in physics. If you ever want to build a wormhole or warp drive, you first need to find yourself a healthy amount of negative mass. By which I mean matter that has negative weight. If that sound weird, it’s because it is: we have no evidence that anything with negative mass actually exists in our universe, and we have very good reasons to suspect it can’t.

Voyage outward

If you’re sufficiently patient, then we’ve already achieved interstellar exploration status. We have several spacecraft on escape trajectories, meaning they’re leaving the solar system and they are never coming back. NASA’s Pioneer missions, the Voyager missions, and most recently New Horizons have all started their long outward journeys. The Voyagers especially are now considered outside the solar system, as defined as the region where the solar wind emanating from the sun gives way to general galactic background particles and dust.

So, great; we have interstellar space probes currently in operation. Except the problem is that they’re going nowhere really fast. Each one of these intrepid interstellar explorers is traveling at tens of thousands of miles per hour, which sounds pretty fast. They’re not headed in the direction of any particular star, because their missions were designed to explore planets inside the solar system. But if any of these spacecraft were headed to our nearest neighbor, Proxima Centauri, just barely 4 light-years away, they would reach it in about 80,000 years.

I don’t know about you, but I don’t think NASA budgets for those kinds of timelines. Also, by the time these probes reach anywhere halfway interesting, their nuclear batteries will be long dead, and just be useless hunks of metal hurtling through the void. Which is a sort of success, if you think about it: It’s not like our ancestors were able to accomplish such feats as tossing random junk between the stars, but it’s probably also not exactly what you imagined interstellar space travel to be like.

Speed racer

To make interstellar spaceflight more reasonable, a probe has to go really fast. On the order of at least one-tenth the speed of light. At that speed, spacecraft could reach Proxima Centauri in a handful of decades, and send back pictures a few years later, well within a human lifetime. Is it really so unreasonable to ask that the same person who starts the mission gets to finish it?

Going these speeds requires a tremendous amount of energy. One option is to contain that energy onboard the spacecraft as fuel. But if that’s the case, the extra fuel adds mass, which makes it even harder to propel it up to those speeds. There are designs and sketches for nuclear-powered spacecraft that try to accomplish just this, but unless we want to start building thousands upon thousands of nuclear bombs just to put inside a rocket, we need to come up with other ideas.

Perhaps one of the most promising ideas is to keep the energy source of the spacecraft fixed and somehow transport that energy to the spacecraft as it travels. One way to do this is with lasers. Radiation is good at transporting energy from one place to another, especially over the vast distances of space. The spacecraft can then capture this energy and propel itself forward.

This is the basic idea behind the Breakthrough Starshot project, which aims to design a spacecraft capable of reaching the nearest stars in a matter of decades. In the simplest outline of this project, a giant laser on the order of 100 gigawatts shoots at an Earth-orbiting spacecraft. That spacecraft has a large solar sail that is incredibly reflective. The laser bounces off of that sail, giving momentum to the spacecraft. The thing is, a 100-gigawatt laser only has the force of a heavy backpack. You didn’t read that incorrectly. If we were to shoot this laser at the spacecraft for about 10 minutes, in order to reach one-tenth the speed of light, the spacecraft can weigh no more than a gram.

That’s the mass of a paper clip.

A spaceship for ants

This is where the rubber meets the interstellar road when it comes to making spacecraft travel the required speeds. The laser itself, at 100 gigawatts, is more powerful than any laser we’ve ever designed by many orders of magnitude. To give you a sense of scale, 100 gigawatts is the entire capacity of every single nuclear power plant operating in the United States combined.

And the spacecraft, which has to have a mass no more than a paper clip, must include a camera, computer, power source, circuitry, a shell, an antenna for communicating back home and the entire lightsail itself.  

That lightsail must be almost perfectly reflective. If it absorbs even a tiny fraction of that incoming laser radiation it will convert that energy to heat instead of momentum. At 100 gigawatts, that means straight-up melting, which is generally considered not good for spacecraft. 

Once accelerated to one-tenth the speed of light, the real journey begins. For 40 years, this little spacecraft will have to withstand the trials and travails of interstellar space. It will be impacted by dust grains at that enormous velocity. And while the dust is very tiny, at those speeds motes can do incredible damage. Cosmic rays, which are high-energy particles emitted by everything from the sun to distant supernova, can mess with the delicate circuitry inside. The spacecraft will be bombarded by these cosmic rays non-stop as soon as the journey begins.

Is Breakthrough Starshot possible? In principle, yes. Like I said above, there’s no law of physics that prevents any of this from becoming reality. But that doesn’t make it easy or even probable or plausible or even feasible using our current levels of technology (or reasonable projections into the near future of our technology). Can we really make a spacecraft that small and light? Can we really make a laser that powerful? Can a mission like this actually survive the challenges of deep space?

The answer isn’t yes or no. The real question is this: are we willing to spend enough money to find out if it’s possible?

Interstellar Travel Could Be Possible Even Without Spaceships, Scientist Says

In about 5 billion years, the Sun will leave the main sequence and become a red giant. It’ll expand and transform into a glowering, malevolent ball and consume and destroy MercuryVenus, Earth, and probably Mars.

Can humanity survive the Sun’s red giant phase? Extraterrestrial Civilizations (ETCs) may have already faced this existential threat.

Could they have survived it by migrating to another star system without the use of spaceships?

Universe Today readers are well-versed in the difficulties of interstellar travel. Our nearest neighboring solar system is the Alpha Centauri system.

If humanity had to flee an existential threat in our Solar System, and if we could identify a planetary home in Alpha Centauri, it would still take us over four years to get there – if we could travel at the speed of light!

It still takes us five years to get an orbiter to Jupiter at our technological stage. There’s lots of talk about generation starships, where humans could live for generations while en route to a distant habitable planet.

Those ships don’t need to reach anywhere near the speed of light; instead, entire generations of humans would live and die on a journey to another star that takes hundreds or thousands of years. It’s fun to think about but pure fantasy at this point.

Is there another way we, or other civilizations, could escape our doomed homes?

The author of a new research article in the International Journal of Astrobiology says that ETCs may not need starships to escape existential threats and travel to another star system.

They could instead use free-floating planets, also known as rogue planets. The article is “Migrating extraterrestrial civilizations and interstellar colonization: implications for SETI and SETA“. The author is Irina Romanovskaya. Romanovskaya is a Professor of Physics and Astronomy at Houston Community College.

“I propose that extraterrestrial civilizations may use free-floating planets as interstellar transportation to reach, explore, and colonize planetary systems,” Romanovskaya writes. And when it comes to the search for other civilizations, these efforts could leave technosignatures and artifacts.

“I propose possible technosignatures and artifacts that may be produced by extraterrestrial civilizations using free-floating planets for interstellar migration and interstellar colonization, as well as strategies for the search for their technosignatures and artifacts,” she said.

It’s possible that rogue planets, either in the Milky Way or some of the other hundreds of billions of galaxies, carry their own life with them in subsurface oceans kept warm by radiogenic decay.

Then if they meet a star and become gravitationally bound, that life has effectively used a rogue planet to transport itself, hopefully, to somewhere more hospitable. So why couldn’t a civilization mimic that?

We think of free-floating planets as dark, cold, and inhospitable. And they are unless they have warm subsurface oceans. But they also offer some advantages.

“Free-floating planets can provide constant surface gravity, large amounts of space and resources,” Romanovskaya writes. “Free-floating planets with surface and subsurface oceans can provide water as a consumable resource and for protection from space radiation.”

An advanced civilization could also engineer the planet for an even greater advantage by steering it and developing energy sources. Romanovskaya suggests that if we’re on the verge of using controlled fusion, then advanced civilizations might already be using it, which could change a frigid rogue planet into something that could support life.

The author outlines four scenarios where ETCs could take advantage of rogue planets.

The first scenario involves a rogue planet that happens to pass by the home world of an ETC. How often that might occur is tied to the number of rogue planets in general.

So far, we don’t know how many there are, but there are certainly some. In 2021, a team of researchers announced the discovery of between 70 and 170 rogue planets, each the size of Jupiter, in one region of the Milky Way. And in 2020, one study suggested there could be as many as 50 billion of them in our galaxy.

Where do they all come from? Most are likely ejected from their solar systems due to gravitational events, but some may form via accretion as stars do.

Another source of rogue planets is our Solar System’s Oort Cloud. If other systems also have a cloud of objects like this, they can be an abundant source of rogue planets ejected by stellar activity.

Romanovskaya writes: “Stars with 1–7 times solar mass undergoing the post-main-sequence evolution, as well as a supernova from a 7–20 times solar mass progenitor, can eject Oort-cloud objects from their systems so that such objects become unbound from their host stars.”

But how often can an ETC, or our civilization, expect a rogue planet to come close enough to hitchhike on? A 2015 study showed that the binary star W0720 (Scholz’s star) passed through our Solar System’s Oort Cloud about 70,000 years ago.

While that was a star and not a planet, it shows that objects pass relatively close by. If the studies that predict billions of free-floating planets are correct, then some of them likely passed close by, or right through, the Oort Cloud long before we had the means to detect them.

The Oort Cloud is a long way away, but a sufficiently advanced civilization could have the capability to see a rogue planet approaching and go out and meet it.

The second scenario involves using technology to steer a rogue planet closer to a civilization’s home. With sufficient technology, they could choose an object from their own Oort Cloud – assuming they have one – and use a propulsion system to direct it towards a safe orbit near their planet.

With sufficient lead time, they could adapt the object to their needs, for example, by building underground shelters and other infrastructure. Maybe, with adequate technology, they could alter or create an atmosphere.

The third scenario is similar to the second one. It also involves an object from the civilization’s outer Solar System. Romanovskaya uses the dwarf planet Sedna in our Solar System as an example.

Sedna has a highly eccentric orbit that takes it from 76 AUs from the Sun to 937 AU in about 11,000 years. With sufficient technology and lead time, an object like Sedna could be turned into an escape ship.

The author notes that “Civilizations capable of doing so would be advanced civilizations that already have their planetary systems explored to the distances of at least 60 AU from their host stars”.

There are lots of potential problems. Bringing a dwarf planet from the distant reaches of the Solar System into the inner Solar System could disrupt the orbits of other planets, leading to all sorts of hazards.

But the dangers are mitigated if a civilization around a post-main sequence star has already migrated outward with the changing habitable zone. Romanovskaya discusses the energy needed and the timing required in more detail in her article.

The fourth scenario also involves objects like Sedna. When a star leaves the main sequence and expands, there’s a critical distance where objects will be ejected from the system rather than remain gravitationally bound to the dying star.

If an ETC could accurately determine when these objects would be ejected as rogue planets, they could prepare it beforehand and ride it out of the dying solar system. That could be extraordinarily perilous, as periods of violent mass loss from the star creates an enormous hazard.

In all of these scenarios, the rogue planet or other body isn’t a permanent home; it’s a lifeboat.

“For all the above scenarios, free-floating planets may not serve as a permanent means of escape from existential threats,” the author explains. “Because of the waning heat production in their interior, such planets eventually fail to sustain oceans of liquid water (if such oceans exist).”

Free-floating planets are also isolated and have fewer resources than planets in a solar system. There are no asteroids to mine, for example, and no free solar energy. There are no seasons and no night and day. There are no plants, animals, or even bacteria. They’re simply a means to an end.

“Therefore, instead of making free-floating planets their permanent homes, extraterrestrial civilizations would use the free-floating planets as interstellar transportation to reach and colonize other planetary systems,” writes Romanovskaya.

In her article, Professor Romanovskaya speculates where this could lead. She envisions a civilization that does this more than once, not to escape a dying star but to spread throughout a galaxy and colonize it.

“In this way, the parent-civilization may create unique and autonomous daughter-civilizations inhabiting different planets, moons, or regions of space.

“A civilization of Cosmic Hitchhikers would act as a ‘parent-civilization’ spreading the seeds of ‘daughter-civilizations’ in the form of its colonies in planetary systems,” she writes. “This applies to both biological and post-biological species.”

Humanity is only in the early stages of protecting ourselves from catastrophic asteroid impacts, and we can’t yet manage our planet’s climate with any degree of stability. So thinking about using rogue planets to keep humanity alive seems pretty far-fetched. But Romanovskaya’s research isn’t about us; it’s about detecting other civilizations.

All of this activity could create technosignatures and artifacts that signified the presence of an ETC. The research article outlines what they might be and how we could detect them. Rogue planets used as lifeboats could create technosignatures like electromagnetic emissions or other phenomena.

An ETC could use solar sails to control a rogue planet or use them on a spaceship launched from a rogue planet once they have reached their destination. In either case, solar sails produce a technosignature: cyclotron radiation.

Maneuvering either a spacecraft or a rogue planet with solar sails would produce “… cyclotron radiation caused by the interaction of the interstellar medium with the magnetic sail”.

Infrared emissions could be another technosignature emitted as waste heat by an ETC on a rogue planet. An excessive amount of infrared or unnatural changes in the amount of infrared could be detected as a technosignature.

Infrared could be emitted unevenly across the planet’s surface, indicating underlying engineering or technology. An unusual mix of different wavelengths of electromagnetic energy could also be a technosignature.

The atmosphere itself, if one existed, could also hold technosignatures. Depending on what was observed, it could contain evidence of terraforming.

For now, astronomers don’t know how many rogue planets there are or if they’re concentrated in some areas of the galaxy. We’re at the starting line when it comes to figuring these things out. But soon, we may get a better idea.

The Vera Rubin Observatory should see first light by 2023. This powerful observatory will image the entire available sky every few nights, and it’ll do it in fine detail. It houses the largest digital camera ever made: a 3.2 gigabyte CCD.

The Vera Rubin will be especially good at detecting transients, that is, anything that changes position or brightness in a couple of days. It’ll have a good chance of spotting any interlopers like rogue planets that might approach our Solar System.

There’s a strong possibility that some of those rogue planets will exhibit unusual emissions or puzzling phenomena. Scientists will probably puzzle over them as they did over Oumuamua.

Maybe another civilization more advanced than us has already faced an existential threat from their dying star. Maybe they made a Herculean effort to capture a rogue planet and engineer it to suit their needs.

Maybe they’ve already boarded it and launched it towards a distant, stable, long-lived yellow star, with rocky planets in its habitable zone. Maybe they’re wondering if there’s any life at their destination and how they might be received after their long journey.

Will Humanity Achieve Interstellar Travel And Find Alien Life?

Although our dreams of making contact with an alien civilization have traditionally been rooted in either a direct visitation or the picking up of an intelligent signal transmitted throughout the galaxy, these remain long-shot possibilities. But real technology may enable us to find worlds where life is abundant and ubiquitous far sooner than we might have expected based on playing this cosmic lottery.

A logarithmic chart of distances, showing the Voyager spacecraft, our Solar System and our nearest star, for comparison. If we ever hope to travel across the great interstellar distances, it will require a technology that’s superior to chemical-based rockets.

The biggest problem with the idea of interstellar travel is scale. The distances to even the nearest stars are measured in light-years, with Proxima Centauri being our nearest neighbor at 4.24 light-years away, where one light-year is approximately 9 trillion kilometers: some 60,000 times the Earth-Sun distance. At the speed of the fastest space probes humanity has ever sent on their way out of the Solar System (the Voyager 1 and 2 spacecraft), covering the distance to the nearest star would take approximately 80,000 years.

But all of this is based on current technology, which uses chemical-based rocket fuel for propulsion. The biggest downside of rocket fuel is its inefficiency: one kilogram of fuel is capable of generating just milligrams’ worth of energy, as measured by Einstein’s E = mc2. Having to carry that fuel on board with you ⁠— and requiring that you accelerate both your payload and the remaining fuel with that energy ⁠— is what’s hamstringing us right now.

Position and trajectory of Voyager 1 and the positions of the planets on 14 February 1990, the day when Pale Blue Dot and Family Portrait were taken. Note that it is only Voyager 1’s position out of the plane of the Solar System that enabled the unique views we retrieved, and that Voyager remains the farthest object ever launched by humanity, but still has thousands of times farther to go until it travels ~4 light-years.

But there are two independent possibilities that don’t require us to dream up Warp Drive-like technologies that would rely on new physics. Instead, we can pursue the routes of either using a more efficient fuel to power our journey, which could increase our range and speeds tremendously, or we can explore technologies where the thrust-providing source is independent of the payload that’s going to be accelerated.

In terms of efficiency, there are three technologies that could vastly outperform chemical-based rocket fuel:

  1. nuclear fission,
  2. nuclear fusion,
  3. and matter-antimatter propulsion.

Whereas chemical-based fuels convert a mere 0.0001% of their mass into energy that can be used for thrust, all of these ideas are far more efficient.

Fission converts approximately 0.1% of the mass of fissile materials into energy; approximately one kilogram of fissionable fuel yields about one gram’s worth of energy, via E = mc2. Nuclear fusion does a superior job; fusing hydrogen into helium, for example, is 0.7% efficient: one kilogram of fuel would yield 7 grams’ worth of usable energy. But far-and-away the most efficient solution is matter-antimatter annihilation.

If we could create and control 0.5 kilograms of antimatter, we could annihilate it at will with 0.5 kilograms of normal matter, creating a 100% efficient reaction that produced a full kilogram’s worth of energy. We could conceivably extract thousands or even a million times as much energy from the same amount of fuel, which could propel us to the stars on timescales of centuries (with fission) or even just decades (with fusion or antimatter).

On the other hand, we could work to achieve interstellar travel via a completely different route: by placing a large power source capable of accelerating a spacecraft in space. Recent advances in laser technology have led many to suggest that an enormous, sufficiently collimated array of lasers in space could be used to accelerate a spacecraft from low-Earth orbit to tremendous speeds. A highly reflective laser-sail, like a solar sail except specifically designed for lasers, could do the job.

If a large-enough, powerful-enough array of in-phase lasers were constructed, potentially reaching gigawatt power levels, it could not only impart momentum to a target spacecraft, but could do so for a long period of time. Based on calculations performed by Dr. Phil Lubin a few years ago, it’s possible that speeds up to 20% the speed of light could be reached. While we don’t yet have a plan for decelerating such a spacecraft, reaching the nearest star in a single human lifetime is within the realm of possibility.

By the same token, the search for extraterrestrial life is no longer restricted to either waiting for an alien visit or searching the Universe with radio signals for intelligent aliens, although the latter is certainly still an active scientific field spearheaded by SETI. Although no signals have been found, this remains a stunning example of high-risk, high-reward science. If a positive detection is ever made, it will be a civilization-transforming event.

However, as exoplanet astronomy continues to advance, two techniques that have already been demonstrated could bring us our first signatures of life on other worlds: transit spectroscopy and direct imaging. Both of these involve using the light from a planet itself, with transit spectroscopy leveraging the light that filters through a planet’s atmosphere and direct imaging taking advantage of the sunlight directly reflected off of the planet itself.

Transit spectroscopy relies on us having a serendipitous alignment of our observatory with both a target exoplanet and its parent star, but these alignments do occur. Whereas a small fraction of the star’s light will get blocked by the transiting planet, an even smaller fraction of starlight will transmit through the planet’s atmosphere, similar to the sunlight that gets transmitted through Earth’s atmosphere and lights up the Moon (in red) during a total lunar eclipse.

This enables us, if our measurements are good enough, to decode what elements and molecules are present in the target planet’s atmosphere. If we could discover biological signatures or even technosignatures  which could be an oxygen-nitrogen atmosphere, complex biomolecules, or even something like a chlorofluorocarbon (CFC) molecule  we would immediately have a strong hint of a living world that would tantalizingly await confirmation.

Direct imaging could provide exactly that sort of confirmation. Although our first image of an Earth-sized exoplanet likely won’t be very visually impressive, it will contain a ton of information that can be used to reveal indicators of life. Even if the planet itself is just one pixel in a detector, we could not only break its light apart into individual wavelengths, but can look for time-varying signatures that could reveal:

-clouds,

-continents,

-oceans,

-plant life greening with the seasons,

-icecaps,

-rotation rates,

and much more. If there are light-emitting signatures at night, just as planet Earth has our light that illuminate the world at night, we could conceivably even detect those as well. If there’s a civilization out there on a nearby Earth-like planet, the next generation of telescopes might be able to find them.

All of this, together, points to a picture where a spacecraft or even a crewed journey to the stars is technologically within our reach, and where the discovery of our first world beyond the solar system with possible life on it could occur in a decade or two. What was once solely in the realm of science-fiction is quickly becoming possible due to both technical and scientific advances and the thousands of scientists and engineers who work to apply these new technologies in practical ways.

How close is humanity to achieving this dream that’s spanned innumerable generations? The first thing you might be wondering is about whether warp drive itself is really feasible or not. And the answer, believe it or not, is maybe, but not unless we figure out a source of energy that goes well beyond anything we’ve got so far, including antimatter.

The reason is simple: to achieve warp drive, you need to bend the space in front of you so that it contracts, and that can only occur at the expense of expanding the space behind you. This takes an enormous amount of energy all localized in one spot, and you need to do it while still keeping the space where your spaceship will be not too severely bent, or you’ll wind up destroying it with terrific gravitational tidal forces.

But if you can do it, and it is something allowed in General Relativity, this requires not only the matter-and-energy we know, but also some form of negative energy: either matter with negative mass or a form of anti-energy itself. If we could harness this, it would mean we could travel through the contracted space (slower than light), but we could do something like contract a 40 light-year journey down to 6 light-months.

Even if we only traveled through that now-contracted space at half the speed of light, we’d get there in 1 year, rather than 40. That’s pretty impressive!

That doesn’t mean, however, that the plot devices or treknobabble cooked up by Star Trek’s writers, which includes things like:

-dilithium crystals,

-warp nacelles,

-Bussard ramjets

-warp cores,

or anything else we might immediately refer to has any relevance. Science fiction provides us with possible outcomes, but only very rarely gets the path to that technological solution correct. We know enough about physics, today, to be certain that Star Trek’s “solution” to this problem is not feasible. But, then again, that’s part of what makes science so wonderful: it can take a fictional idea and make it a reality. Or, if we’re really lucky, surpass our sci-fi dreams!

A representation of an alien invasion. This is not an actual extraterrestrial.FLICKR USER PLAITS

Aliens, on the other hand, are likely ubiquitous, based on what we know about the ingredients for life in the Universe, the workings of chemistry, and our measurements of exoplanets with the right conditions for life around other stars. We have literally billions and billions of potentially habitable planets in our galaxy alone, with similar conditions to early Earth. In many models, early Venus and Mars were similar to early Earth.

Are we supposed to believe that Earth, where life arose within the first ~3% of our planet’s history, is somehow unique in that regard? Although winding up with something like human beings is a difficult proposition, winding up with no life at all, across billions and billions of other instances with similar initial conditions, seems far more unlikely, at least from a scientific perspective.

In the 1920s, we didn’t know the Universe was expanding, but its discovery led to the idea of the Big Bang. In the 1960s, we didn’t know that the Big Bang was true, but its confirmation led to questions about what came before it and what our Universe’s ultimate fate would be.

And now, as you can see, we’re talking about the mysteries of cosmic inflation and dark energy, which are where those frontiers now lie. And in any field, this is how it works: discovering an answer only reveals a deeper frontier that we haven’t yet explored.

Science is all about discovering and following the rules; science-fiction is about breaking those rules. I haven’t explicitly thought about it in those terms, and I agree that this is pretty much how it usually works. I don’t know that this is why I, personally, like or don’t like various forms of science-fiction, but it’s a new perspective to think about for me.

We constantly have advancing technology, and science-fiction asks the question of how advancing technology will change our lives.

Visualizations, based on a mix of science and artistic license, have been around for as long as we’ve even known enough about science to imagine what could realistically be. Also, side note, the “interstellar” black hole is probably not very likely to be what we see when we examine our realistic black holes in supreme accuracy; there’s a lot of artistic license and some likely unphysical assumptions that were made for Insterstellar.

Do you know why things like rockets and space shuttles have the shapes they do? That elongated, narrow-cone shape you’re familiar with? It’s because of atmospheric drag.

If you’re going to build your ship in space, and fly it only in space, you don’t need to factor in aerodynamic considerations at all! You’d be much, much smarter to build a structure with a good volume-to-surface-area ratio: a sphere. The Death Star, not the Millennium Falcon or an X-Wing, is going to be much more practical for structures we build in space!

Ion drives are real, and they’re very cool. But if you want to power a journey across large distances in a reasonable amount of time, ion drives won’t get you far at all. They can take you ~6 billion kilometers over 11 years, as Bryan said, and can do so pretty efficiently. But if you factor that distance over that time as a “mean acceleration,” you get something truly atrocious: 100 nanometers/second^2.

You’re… not going to go very far very fast. ~100,000 years to the nearest star, same as conventional fuel. Obviously not a viable option.

Solar Sails

You accelerate with a solar sail and you can also decelerate with a solar sail! The “fuel” is simply radiation provided by a star, so as long as you visit a star comparable to the Sun, you could decelerate the same way you accelerated.

Unfortunately, this technology is inferior to ion drives not only in terms of distance reached, but in terms of acceleration and control over your spacecraft. It’s a nice idea, but it’s an idea that’s in its infancy, at best, despite being proposed more than 400 years ago by Johannes Kepler!

Quantum Teleportation doesn’t involve teleporting a particle, it involves teleporting the quantum state of a particle. This doesn’t solve the problem of teleporting an inanimate object, much less a person.

You need a lot of information to encode a human being. Remember that there are around ~10^28 atoms in the human body, and that means something like 10^29 or 10^30 quantum bits of information. As Bryan says, “I don’t think we’ll be teleporting anytime soon.”

Time dilation could be a viable option for interstellar travel. If you wanted to go more than ~100 light-years, it would always take you more than ~100 years (a human lifetime, at the far end) to get there from the frame-of-reference of a person remaining on Earth.

But if you continue to accelerate at 1 g, or 9.8 m/s^2, you’ll get to wherever you want to go in a much shorter timescale from your frame of reference, as you travel close to the speed of light.

Using the transit method, we can find out properties of the planets that orbit around the stars, and they come in enormous varieties, just like we’d expect if we didn’t assume the rest of the Universe was just like our little corner. We’ve found the planets that are easiest to find, and that means the largest planets relative to their star in close-in orbits. This, unsurprisingly, has skewed the population of planets that we’ve found.

Resources

space.com, “Is Interstellar Travel Really Possible?” By Paul Sutter; sciencealert.com, “Interstellar Travel Could Be Possible Even Without Spaceships, Scientist Says.” By Evan Gough; forbes.com, “Will Humanity Achieve Interstellar Travel And Find Alien Life?” By Ethan Siegel;

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