Our favorite Graybeard has written a concise, well-stated piece on interstellar travel, and why it’s currently out of the question. Barring a huge surprise in physics, that adverb “currently” might better be “permanently,” for a simple reason Graybeard gives:
Voyagers 1 and 2 are the farthest man made objects from us, and have been traveling for 47 years. As I’ve said before:
Voyager 1 is currently 22 hours, 37 minutes and change away at light speed. I’ll call it 22-1/2 light hours away. The nearest stars are just over four light years away. Assuming it’s even going in the right direction, it’ll take Voyager 1 almost 77,000 years to get to the Alpha/Proxima Centauri star system.
It’s safe to say that there’s no way we could mount a mission to the nearest star with any technology we know of. What moving machines do you know of that could work for 77,000 years?
Don’t ask me to design one. But there’s another obstacle that looks just as compelling as the problem of the lightspeed barrier: Newton’s Third Law, a.k.a. the Conservation of Momentum. For a body of non-zero mass to acquire a velocity in one direction, it must eject mass at an appropriate speed in the opposite direction.
Not only do we not have the time to get to the nearest star; we don’t have the mass.
I’ve just done forty years of offhand, back-of-the-envelope calculations – Yes, really! Finished ‘em just this minute. Remarkable, isn’t it? – and I’ve reached the conclusion that even were we capable of using the whole mass of the Sun to accelerate a “generation ship” (Cf. Orphans of the Sky), not only wouldn’t we get anywhere fast enough to be worthwhile; we’d also piss off the galactic neighborhood by flinging all that high-speed mass at them. Worse, we wouldn’t have any mass with which to slow down when we neared our destination.
Science-fiction writers have either ignored this limitation completely or have postulated loopholes in physics: “inertialess” ships / drives; “wormholes” and alternate spaces “above” or “beneath” our universe; or methods for altering the laws of physics around the ship (my favorite.) But these are mere speculations. None of them are possible as we understand the laws of physics today.
Will our understanding change again in the foreseeable future? I can’t say either way. Such changes have occurred in the recent past: e.g., the discovery that certain quantum-mechanical phenomena can only be explained by postulating temporary violations of the Law of Conservation of Mass-Energy. All the same, I’m not going to put a deposit down on any extrasolar real estate just yet.
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The nearest star to the sun is 104 million times farther away than the moon is to the earth. Few people grasp just how immense the galaxy is and there are 100 billion galaxies. To talk about interstellar travel is to misunderstand the concept of travel. Discussion of propulsion systems or fuel is like a marathon runner discussing which shoes would be best for his run across the Atlantic.
I can’t say its impossible but the Star Wars or Star Trek realities are incredibly unlikely.
Bussard Ramjet
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Have you built one? When is the first public test scheduled?
An interesting object lesson about how incredibly empty Space actually is can be found here: https://www.joshworth.com/dev/pixelspace/pixelspace_solarsystem.html
It gives a tediously accurate scale model of the Solar System, where the diameter of Earth’s Moon is exactly one pixel. Just the solar system, mind.
Fun Fact: You could fit all seven of the current planets, lined up side by side, into the gap between the Earth and the Moon. (On those infrequent occasions when the Moon is at apogee, you could even fit in Pluto.)