By the end of 21st century C.E. quantum computer could handle billions of calculations within fraction of a second and run multiple tasks simultaneously, and they are everywhere except on spacecraft, at least, of the commercial type. It appears that many nations have banned the use of qubit systems for all commercial interstellar flight.

I'm trying to come up with the side effect of using such a system which could be hazardous for interstellar travel and of no avail. (The Alcubierre drive has become affordable and reliable.)


closed as primarily opinion-based by Aify, John Dallman, Hohmannfan, JDługosz, Azuaron Nov 11 '16 at 14:10

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  • $\begingroup$ Just a note I'm comparing adiabatic quantum computing with classical transistor based processes. $\endgroup$ – user6760 Nov 11 '16 at 7:35
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    $\begingroup$ My phone can do billions of calculations a second ;) $\endgroup$ – Samwise Nov 11 '16 at 21:47
  • $\begingroup$ They with to prevent emerging of an AI, on earth it can be handled like in a bottle, in space it may escape in any direction it prefers. $\endgroup$ – MolbOrg Nov 12 '16 at 10:38

Quantum computers don't handle billions of calculations within a fraction of a second. Their real behavior would be a reason they may not be trusted.

Quantum computers are inherently statistical beasts. As such, any part of our society where we are unwilling to leave anything to chance would not have love for a quantum computer.

Today, the FAA is notorious for being one of the more demanding clients for reliable real time computers. It would not be unreasonable to assume their future equivalent is just as demanding.

  • $\begingroup$ I thought bremermann's limit cannot be imposed on a quantum computer therefore theoretically it could go beyond petaflop as such, no? $\endgroup$ – user6760 Nov 11 '16 at 7:15
  • $\begingroup$ @user6760 Its not that they can do a lot of operations, its that they do things that are different from the operations we are used to thinking about. A quantum computer would actually be very slow at floating point operations, because that's not a natural form for it. A quantum computer would be good at operations on a real numberline, and it makes its living on systems that leverage superposition. It's an example of "work smarter, not harder." Quantum computers typically aren't fast, they're just really really efficient at some algorithms. $\endgroup$ – Cort Ammon Nov 11 '16 at 16:14

Exotic radiation

Already today, it is not very easy to bring a computer into space, even with our (relatively speaking) very primitive silicon based Boolean logical computers.

On the ground we are spared the threat of cosmic radiation of most sorts because the atmosphere provides a thicket of annoying air molecules that get in the way of such rays before they have the chance to reach the silicon chips and play with them.

In space it is a different matter. There you have a diverse population of subatomic particles that make up a "colorful" spectrum of cosmic radiation. And these particles/rays do bad things when they get into a silicon chip. At worst they will actually start destroying the semiconductor components. At "best" they will saturate instruments (which is how we discovered that space is teeming with these things in the first place) or start flipping bits on your hard drives and/or volatile memory, zeroes becoming ones and vice versa.

And considering how we discovered the Van Allen Belts just very recently, despite them being right in our proverbial back yard, who knows what interesting things we will find when we get out into space for real. We still have no idea for instance how Dark Energy and Dark Matter behaves. And we cannot say for certain that the laws of nature are actually constant or if they will start behaving queer once we get out into the wide black yonder.

Thus you can hand-wave it like so: just as Explorer 1 went bonkers once it actually got out there, due to radiation we did not really expect to find (even though some scientists had predicted it), invent some kind of radiation that does something similar with your quantum computers. A phenomenon that for the moment is being researched but that is poorly understood by the time your story is set. Patches, areas or even whole regions beset by this radiation would provide excellent plot hooks for you, a well of different scenarions that you can choose from.

  • $\begingroup$ That cosmic radiation will probably be harmful to humans and would require shielding anyway. $\endgroup$ – Cem Kalyoncu Nov 12 '16 at 16:14
  • $\begingroup$ @CemKalyoncu Not necessarily. Compare neutrinos for instance. Or plain old electromagnetic pulses. $\endgroup$ – MichaelK Nov 13 '16 at 10:16
  • $\begingroup$ @CemKalyoncu Reasonable levels of radiation wouldn't be a problem for humans, if we've cured cancer (and a few other things) by then. We're much less delicate than artificial quantum superpositions. $\endgroup$ – Maxander Jan 13 '17 at 20:54
  • $\begingroup$ Yes we are however, outer space has serious amounts of radiation. A thick lead armor will block it all, it is doable with today's technology, well, apart from the added weight. And for neutrinos, there are more of them on earth then intergalactic flights. $\endgroup$ – Cem Kalyoncu Jan 14 '17 at 6:22

There are couple of problems related with this technology:

  • Quantum computers are not fast in traditional sense: they are massively parallel thus single threaded systems like navigation may not be suitable for it
  • Quantum computers are probabilistic. This means there is a fair chance (99.9% per logic gate) that the result of the calculation is wrong. It can be detected but it will delay any instantaneous action required for the navigation.
  • $\begingroup$ probability of wrong result you can choose which probability is enough for you, it is not a fixed value. $\endgroup$ – MolbOrg Nov 12 '16 at 10:36

Quantum computers effectively run all possible calculations simultaneously. Current quantum computers are fragile systems and can only handle a few qubits at best. By the time interstellar travel has been developed it is not unreasonable to assume quantum computers have developed to the stage where they are as common as conventional non-quantum computers. All the factors that make quantum computers will have fixed. They work well, their operations stable, robust and reliable.

However, when spacecraft travel beyond the confines of our solar system the reliability of quantum computers disappears, their operations become so erratic that they can no longer be trusted to control the systems of an interstellar spacecraft.

The cause is simple. In a planetary system such as our solar system there is sufficient matter in relatively close proximity to damp out any interference effects emanating from all other versions of a quantum computer in the multiverse. Since there will be an infinite number of different versions of any quantum computer across the multiverse the uncertainty in its operations will also become infinitely uncertain. When the damping effect is no longer present states in a quantum computer no longer correspond to any given program running on it. This effect will become progressively worse the further from any large masses like stars and planetary systems the starship travels.

Quantum computers can used reliably on interplanetary spacecraft and inside planetary systems, but in the depths of interstellar travel they are too hazardous to use.


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