The trouble with Copenhagen


Copenhagen - Vesterbro
Copenhagen – Vesterbro (Photo credit: Valerio Fuoglio)

Dr Johnson famously settled an argument on the existence or non-existence of the physical universe by kicking a heavy stone and saying “I refute it thus”.

But when it comes to the science of the micro-universe, the quantum world, no heavy stones seem to be around to be kicked.

I have been thinking about this since I posted a blog about Antony Valentini‘s idea that we could use some very rare particles to communicate at a speed faster than the speed of light.

Valentini’s challenge is to the “Copenhagen interpretation” of what quantum mechanics appears to tell us.

The fundamental difficulty with quantum mechanics is that it says we cannot know, with total accuracy, the position and momentum of a particle. This “uncertainty” is what creates the “spooky interaction at a distance” – because if we measure the momentum of one paired particle then uncertainty and energy conservation laws “appear” to make the other particle assume a certain state instantaneously.

In the “Copenhagen interpretation” we are essentially asked to accept that this is due to an instantaneous “collapse” of the physical laws we have been using to this point. It’s as if our quantum rules are just a window on to a “real” physical world and that our poking shakes up what is going on behind the scenes in ways we cannot hope to understand.

That’s not very convincing, though (even if it “works”).

So, what are the alternatives?

Valentini is reviving an idea of Louis DeBroglie that was rejected in favour of the “Copenhagen interpretation”: namely that our paired particles remain linked by a “pilot wave” that communicates the state change instantly.

That, though, appears to offend against the physics of the world of general relativity – we are conditioned to think such instant communication is impossible because our physics tells us that we need infinite energy to move a massive body at the speed of light: hence making that an unbreakable speed limit.

And then there is the “many worlds” interpretation – namely that all that might happen does happen and so there are an infinite number of those paired particles and “our universe” is just one of an infinite number.

None of them really seem that satisfactory an explanation.

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Why we’ll never meet aliens


First page from the manuscript explaining the ...
First page from the manuscript explaining the general theory of relativity (Photo credit: Wikipedia)

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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