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rhythmaningIt was a birthday a couple of weeks ago, and the guys I work with gave me a card: one of those 3-d cards where the picture changes as you tip the card. This one showed a beer glass, and as I changed the angle, it started full, then half full, then empty. (I am a glass-half-full kind of a bloke.) I was saying thank you, and I described the beer straight as being like Schrodinger’s beer mug: simultaneously full and empty, and impossible to say which it was.
I got a very blank look back.
You know, I said, like Schrodinger’s cat – neither alive nor dead.
The blank look got blanker.
So I tried to explain Schrodinger’s cat – the thought experiment he used to show the inherent absurdity of quantum mechanics extrapolated into the real world. And I realised how hard it was to explain these things; and how I didn’t really understand it myself. (There is no reason I should; I am neither a physicist nor a mathematician; but I have read popular science books about quantum physics, and I thought I understood it.)
That afternoon, another colleague told how she had taken her young children to the opening of the Edinburgh Science Festival the night before, so I looked at the festival website and saw several talks that interested me; the first was by Marcus Chown – called “Quantum Theory Can’t Hurt Us”, the apposite randomness seemed appropriate. I decided to go along.
The lecture was introduced by Prof Heinz Wolff. This too seemed very apposite: many years ago, as a young teenager interested in science, I went along to talks at the Hampstead Scientific Society, where Heinz Wolff would chair and introduce the meetings. I went to lots of lectures there; one I remember was about relativity (I can’t remember the speaker – it was about 35 years ago, after all!): I recall understanding everything that was said, until I left the lecture theatre, when none of it seemed quite to tie up.
In the lecture theatre of the Royal Scottish Museum, Prof Wolff described exactly the same feeling: he said he had been to lots of talks about quantum theory, and they made sense at the time; but the sense seemed to decay quickly – he estimated the half life of knowledge about quantum mechanics to be about twelve hours. (So I am writing about it now, several days later, to see what I have retained; I took lots of notes – it is how I remember things – but I intend not to look at them at all, until I have finished; and then I’ll tidy this up a bit. They will be the bits in square brackets…)
Chown actually spoke about relativity and quantum theory: the very large scale and the very small: the two towering scientific achievements of the 20th century He started with relativity, and he explained it well. The theory grew out of Einstein’s awareness, apparently at the very young age of 16, that it was not possible that both the classical theory of motion – essentially the theories of Galileo and Newton – and the new theories of electro-magnetics developed by James Clerk Maxwell could hold: coming out of electro-magnetics was that the speed of light was constant, whilst Newtonian mechanics meant that objects could be accelerated faster and faster. (I have to take all this to be true: Chown fortunately avoided proving this – or anything – with equations. I was happy to accept this as a truth.)
[The story was that the sixteen year old Einstein had envisaged what would happen if you travelled at the speed of light – whether you would catch the light up – and reckoned that a light beam must be uncatchable. This would be true irrespective of the direction of travel – so light must have the same speed irrespective of the observer: travelling towards a light at the speed of light would mean the combined speeds were still only the speed of light.]
Chown described how Einstein worked out that if nothing could go faster than the speed of light, time must slow down for objects as they approached the speed of light – but not for observers (hence speed and time were relative); this has been proven by monitoring the decay of particles called muons: created through the interaction between high energy radiation (that’ll be “cosmic rays” to you and me) and the upper atmosphere 12.5 km above the Earth, muons rapidly decay before they have travelled very far. They travel at close to the speed of light – 99.92%: and time is slowed down for them that they survive long enough to reach Earth, where they can be detected. (There was a demonstration of this in the museum.) Because time has slowed down from their perspective, muons travel further than they ought, 12.5 km instead of 250m, to reach Earth-bound detectors.
Chown explained other aspects of relativity – gravity being a field which is warped by mass, the possibility for time travel, and the possible creation of black holes (although he didn’t discuss the fears of some that the large hadron collider at CERN might create mini-black holes which will engulf the universe) – and with one leap we moved from the very large scale to the very small – and so to quantum theory.
This, Chown asserted, arose out of another conflict between two theories: James Clerk Maxwell’s that light (and all electro-magnetic radiation) are waves, and that they are also particles. This can be shown through another link to relativity: light particles – photons – can be deflected by large, massive objects (like the Sun) in ways which particles would be and waves wouldn’t. It can also be shown that particles – say, electrons – can behave like waves: streams of particles beamed through diffraction slits show interference patterns (Chown mentioned this in a specific case – a single particle passing through a diffraction slit; the more general case I remember from some time ago). So again, we have a quandary: a single entity – light or electrons (or whatever) behaving both as particles and as waves.
Quantum theory sorts this out – again, Chown mercifully didn’t go into the details of how it sorts it out, but I’ll take his word for it that it does. He described some effects: the probabilistic nature of matter (which takes us back to Schrodinger and his cat, which Chown mentioned: the thought experiment was based on the random decay of a radioactive atom, the effect of which would kill a cat in a box: since the radioactive decay is random, at any one time it was not possible to tell whether the cat was alive or dead without looking. Instead, there was a probability that the cat was either alive or dead – and so it was simultaneously alive and dead). The wave/particle structure of matter has lots of implications: it is not possible to say where atomic particles are (and, if I recall, the uncertainty principle is such that if you could, the observation itself would cause the particle to be somewhere else); indeed, it is possible for a particle to be in two places, or even everywhere, at once.
Einstein didn’t buy into this at all: he famously said “God doesn’t play dice with the universe!” Chown quoted Stephen Hawking, who said not only does God play dice with the universe, he throws the dice where we can’t see them.
Chown asserted that as much as 70% of the economy of the USA is based on the quantum behaviour of particles. I assume that this is because much of electronics is based on quantum mechanics – transistors, I think; and I believe that mobile phone technology depends on it, too. Computers, too.
And at this point, Chown went on to talk about quantum computers, at which point my head exploded. He lead into this through the observation that firing a single particle through a pair of diffraction slits shows interference patterns. A single photon, mind: a single photon which can only pass through a single slit, and hence have nothing to interfere with on the other side of the slit. (Can you feel my head explode? Or maybe it is just a probabilistic explosion – a tendency to explode, perhaps.) Apparently, some physicists believe that the interference arises because in this universe the particle passed through one slit, and in an alternate universe, it passed through the other; and then the two particles in different universes interfere with each other. (I have no idea how they would communicate between two separate universes.) I really can’t remember the specifics about quantum computers, except that they would be very powerful, and, possibly by utilising an infinite number of alternate universes, could do more calculations that there were particles in the universe.
Kind of freaky stuff.
And I am rather pleased at how much I have been able to remember. Even if I don’t necessarily understand it all.
Edit: And no one noticed I had spelt Schrodinger wrong...
Schrodinger’s beer glass … full.
I got a very blank look back.
You know, I said, like Schrodinger’s cat – neither alive nor dead.
The blank look got blanker.
So I tried to explain Schrodinger’s cat – the thought experiment he used to show the inherent absurdity of quantum mechanics extrapolated into the real world. And I realised how hard it was to explain these things; and how I didn’t really understand it myself. (There is no reason I should; I am neither a physicist nor a mathematician; but I have read popular science books about quantum physics, and I thought I understood it.)
That afternoon, another colleague told how she had taken her young children to the opening of the Edinburgh Science Festival the night before, so I looked at the festival website and saw several talks that interested me; the first was by Marcus Chown – called “Quantum Theory Can’t Hurt Us”, the apposite randomness seemed appropriate. I decided to go along.
* * *
The lecture was introduced by Prof Heinz Wolff. This too seemed very apposite: many years ago, as a young teenager interested in science, I went along to talks at the Hampstead Scientific Society, where Heinz Wolff would chair and introduce the meetings. I went to lots of lectures there; one I remember was about relativity (I can’t remember the speaker – it was about 35 years ago, after all!): I recall understanding everything that was said, until I left the lecture theatre, when none of it seemed quite to tie up.
In the lecture theatre of the Royal Scottish Museum, Prof Wolff described exactly the same feeling: he said he had been to lots of talks about quantum theory, and they made sense at the time; but the sense seemed to decay quickly – he estimated the half life of knowledge about quantum mechanics to be about twelve hours. (So I am writing about it now, several days later, to see what I have retained; I took lots of notes – it is how I remember things – but I intend not to look at them at all, until I have finished; and then I’ll tidy this up a bit. They will be the bits in square brackets…)
Chown actually spoke about relativity and quantum theory: the very large scale and the very small: the two towering scientific achievements of the 20
[The story was that the sixteen year old Einstein had envisaged what would happen if you travelled at the speed of light – whether you would catch the light up – and reckoned that a light beam must be uncatchable. This would be true irrespective of the direction of travel – so light must have the same speed irrespective of the observer: travelling towards a light at the speed of light would mean the combined speeds were still only the speed of light.]
Chown described how Einstein worked out that if nothing could go faster than the speed of light, time must slow down for objects as they approached the speed of light – but not for observers (hence speed and time were relative); this has been proven by monitoring the decay of particles called muons: created through the interaction between high energy radiation (that’ll be “cosmic rays” to you and me) and the upper atmosphere 12.5 km above the Earth, muons rapidly decay before they have travelled very far. They travel at close to the speed of light – 99.92%: and time is slowed down for them that they survive long enough to reach Earth, where they can be detected. (There was a demonstration of this in the museum.) Because time has slowed down from their perspective, muons travel further than they ought, 12.5 km instead of 250m, to reach Earth-bound detectors.
Chown explained other aspects of relativity – gravity being a field which is warped by mass, the possibility for time travel, and the possible creation of black holes (although he didn’t discuss the fears of some that the large hadron collider at CERN might create mini-black holes which will engulf the universe) – and with one leap we moved from the very large scale to the very small – and so to quantum theory.
This, Chown asserted, arose out of another conflict between two theories: James Clerk Maxwell’s that light (and all electro-magnetic radiation) are waves, and that they are also particles. This can be shown through another link to relativity: light particles – photons – can be deflected by large, massive objects (like the Sun) in ways which particles would be and waves wouldn’t. It can also be shown that particles – say, electrons – can behave like waves: streams of particles beamed through diffraction slits show interference patterns (Chown mentioned this in a specific case – a single particle passing through a diffraction slit; the more general case I remember from some time ago). So again, we have a quandary: a single entity – light or electrons (or whatever) behaving both as particles and as waves.
Quantum theory sorts this out – again, Chown mercifully didn’t go into the details of how it sorts it out, but I’ll take his word for it that it does. He described some effects: the probabilistic nature of matter (which takes us back to Schrodinger and his cat, which Chown mentioned: the thought experiment was based on the random decay of a radioactive atom, the effect of which would kill a cat in a box: since the radioactive decay is random, at any one time it was not possible to tell whether the cat was alive or dead without looking. Instead, there was a probability that the cat was either alive or dead – and so it was simultaneously alive and dead). The wave/particle structure of matter has lots of implications: it is not possible to say where atomic particles are (and, if I recall, the uncertainty principle is such that if you could, the observation itself would cause the particle to be somewhere else); indeed, it is possible for a particle to be in two places, or even everywhere, at once.
Einstein didn’t buy into this at all: he famously said “God doesn’t play dice with the universe!” Chown quoted Stephen Hawking, who said not only does God play dice with the universe, he throws the dice where we can’t see them.
Chown asserted that as much as 70% of the economy of the USA is based on the quantum behaviour of particles. I assume that this is because much of electronics is based on quantum mechanics – transistors, I think; and I believe that mobile phone technology depends on it, too. Computers, too.
And at this point, Chown went on to talk about quantum computers, at which point my head exploded. He lead into this through the observation that firing a single particle through a pair of diffraction slits shows interference patterns. A single photon, mind: a single photon which can only pass through a single slit, and hence have nothing to interfere with on the other side of the slit. (Can you feel my head explode? Or maybe it is just a probabilistic explosion – a tendency to explode, perhaps.) Apparently, some physicists believe that the interference arises because in this universe the particle passed through one slit, and in an alternate universe, it passed through the other; and then the two particles in different universes interfere with each other. (I have no idea how they would communicate between two separate universes.) I really can’t remember the specifics about quantum computers, except that they would be very powerful, and, possibly by utilising an infinite number of alternate universes, could do more calculations that there were particles in the universe.
Kind of freaky stuff.
And I am rather pleased at how much I have been able to remember. Even if I don’t necessarily understand it all.
Schrodinger’s beer glass … empty.
Edit: And no one noticed I had spelt Schrodinger wrong...