Well, the answer is pretty plain: Einstein‘s theory of general relativity – which even in the last month has added to it’s already impressive list of predictive successes – tells us that to travel at the speed of light a massive body would require an infinite amount of propulsive energy. In other words, things are too far away and travel too slow for us to ever hope to meet aliens.
But what if – and it’s a very big if – we could communicate with them, instantaneously? GR tells us massive bodies cannot travel fast, or rather along a null time line – which is what really matters if you want to be alive when you arrive at your destination – but information has no mass as such.
Intriguingly, an article in the current edition of the New Scientist looks at ways in which quantum entanglement could be used to pass information – instantaneously – across any distance at all. Quantum entanglement is one of the stranger things we can see and measure today – Einstein dismissed it as “spooky interaction at a distance” – and essentially means that we can take two similar paired particles and by measuring the state of one can instantaneously see the other part of the pair fall into a particular state (e.g., if the paired particles are electrons and we measure one’s quantum spin, the other instantly is seen to have the other spin – no matter how far away it is at the time).
Entanglement does not allow us to transmit information though, because of what the cosmologist Antony Valentini calls, in an analogy with thermodynamic “heat death”, the “quantum death” of the universe – in essence, he says that in the instants following the Big Bang physical particles dropped into a state in which – say – all electron spins were completely evenly distributed, meaning that we cannot find electrons with which to send information – just random noise.
But – he also suggests – inflation – the super-rapid expansion of the very early universe may also have left us with a very small proportion of particles that escaped “quantum death” – just as inflation meant that the universe is not completely smooth because it pushed things apart at such a rate that random quantum fluctuations were left as a permanent imprint.
If we could find such particles we could use them to send messages across the universe at infinite speed.
Perhaps we are already surrounded by such “messages”: those who theorise about intelligent life elsewhere in the universe are puzzled that we have not yet detected any signs of it, despite now knowing that planets are extremely common. That might suggest either intelligent life is very rare, or very short-lived or that – by looking at the electromagnetic spectrum – we are simply barking up the wrong tree.
Before we get too excited I have to add a few caveats:
- While Valentini is a serious and credible scientist and has published papers which show, he says, the predictive power of his theory (NB he’s not the one speculating about alien communication – that’s just me) – such as the observed characteristics of the cosmic microwave background (an “echo” of the big bang) – his views are far from the scientific consensus.
- To test the theories we would have to either be incredibly lucky or detect the decay products of a particle – the gravitino – we have little evidence for beyond a pleasing theoretical symmetry between what we know about “standard” particle physics and theories of quantum gravity.
- Even if we did detect and capture such particles they alone would not allow us to escape the confines of general relativity – as they are massive and so while they could allow two parties to theoretically communicate instantly, the parties themselves would still be confined by GR’s spacetime – communicating with aliens would require us and them in someway to use such particles that were already out there, and perhaps have been whizzing about since the big bang itself.
But we can dream!
Update; You may want to read Andy Lutomirski’s comment which, I think it’s fair to say, is a one paragraph statement of the consensus physics. I am not qualified to say he’s wrong and I’m not trying to – merely looking at an interesting theory. And I have tracked down Anthony Valentini’s 2001 paper on this too.
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7 responses to “Why we’ll never meet aliens”
Sorry, quantum mechanics doesn’t work like that.
Let’s be very optimistic. Suppose you find a whole bunch of particles that are perfectly entangled with far-away aliens. You still can’t communicate, because of the “no-signaling” or “no-communication” theorem. Entanglement is neat, but it’s nowhere near that powerful.
Thanks for the comment.
Plainly I did not explain this very well – the point the article makes is that we (think we) cannot signal because quantum states are perfectly distributed – ie “quantum death” has occurred. But if there were “undead” particles out there then we could communicate.
It is amazing to me that people never think out of the box, Einsteins speed limit will be broken, there is no doubt about that. An extraterrestrial race may have developed technology that makes Einsteins theory look like first grade math problem. Man is only held back by thinking that he can’t do something or that he was told by an ‘expert’ that it was impossible to go beyond a certain theory!
Thanks for the comment, but I don’ agree with any of it!
Why couldn’t an alien race that has lived millions of years longer than humans have advanced their technology to the point where they could travel the stars? Gravity itself can bend space enough to jump a large distance, human tech is only a spec in time and look how far it has come. An alien race having technology evolving for millions of years could very possibly have created something to do what we think is impossible right now.
Because they’d need infinite energy to travel at the speed of light. If you have an alternative physics please publish it. Otherwise you might as well say “what if the Moon were made of cheese?”
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