If you take a cat, put it in a box with a poison vial that will rupture when a radioactive source within the box decays, and close the box, you’ll more than likely end up with a criminal record, or leave Mum a messy surprise for when she gets home from work. However, proposing this in the world of Physics will actually bag you some street cred, and open up more than a few fiery debates. This experiment was indeed proposed by the late Erwin Schrodinger, a contemporary of Einstein back in 1935, and what he proposed should amaze you.
Schrodinger, a pioneer in quantum physics, proposed that until the box is opened and the fate of the cat revealed, our feline friend can be considered both alive and dead at the same time, in other words, existing in a state of superposition. If this amazes you (it should), prepare to tumble down the rabbit hole of an area of Physics called Quantum Mechanics, a field who’s theories attempt to demystify so much of the phenomena that we observe in the world around us, but is however, understood by so few.
Quantum mechanics concerns itself mainly with the behaviour of subatomic particles. For the uninitiated, subatomic particles are essentially the building blocks of literally everything we see around us, and also of the infinitely large Universe that we find ourselves in. By taking a look at your current surroundings, you may fall into the trap of thinking that you have the Physical world pretty much cracked. The phone or laptop that you are using to read this is solid, and therefore must be made up of things that can only themselves be solely described as solid. When you are not looking at your device, it behaves just as it would as when you are, and therefore the things that make it up must also behave in a similar fashion. The device you are reading this from isn’t physically connected to anything else (aside from a portable charger perhaps), and therefore could not be affected by similar objects light years away, so the things that make it up cannot be either. I hate to break it to you, but this seemingly fair bit of reasoning is in fact considered wrong in the world of Quantum Mechanics, and I’m going to try and explain as best I can why that is.
Taking the first statement, that the things that make up your solid device must also be solid themselves. If you agree with this, then Louis De Broglie (pronounced ‘Broy’ not ‘Broccolli’) will beg to differ. A hypothesis of his based upon experimental data from 1924 suggested that electrons, and by extension everything that they make up (so… everything), actually have wavelengths, meaning under certain situations, they can behave like waves, and at other times, like particles. This was first demonstrated when electrons fired at a screen, were shown to diffract (spread out), behaviour shown only by waves. This experiment caused quite the ruckus among Physicists of the time, and understandably so. Imagine someone telling you that the chair you’re sitting on right now had a wavelength!
In the case of the second statement, that when you look away from your device, it behaves in the same manner as if you were looking at it, and therefore that the stuff its made of should as well, is also sadly wrong. In an infamous experiment first devised by Thomas Young, electrons were fired through a screen with two tiny vertical slits in. After passing through, you would expect to see to vertical lines directly behind the slits where the electrons had hit the screen. The result however, was far more interesting. These electrons had in fact diffracted (as mentioned before), even when fired through one at a time! They had been shown to be interfering with themselves. Physicists, ever curious, set up complicated devices to see what was going on, as it appeared that these electrons were existing in superposition (more than one place at once), but when the experiment was re run, with measurements being taken, these mischevious electrons went back to behaving like particles, forming two distinct lines behind the screen. It seems, even today, that electrons radically change behaviour when being observed (don’t worry, I don’t understand this at all either).
Dealing with the final statement, that without physical connection, the device you’re reading this from shouldn’t be affected by anything, and therefore neither should the particles that make it up, is also wrong. This is perhaps the spookiest of all, or so said Albert Einstein. Electrons, much like everything else in the world, have properties. Not houses or flats, but characteristics that define them. One such property is spin. They’re not actually spinning (take it up with Wolfgang Pauli), but are different depending on whether they’re spinning up, or spinning down. When two electrons are separated, and the spin of one observed, you can say with absolute certainty that the spin of the other will be the opposite, nothing amazing right? However, imagine these particles are separated by astronomical (excuse the pun) distances, with no physical connection, and the spin of one is observed, what happens? You guessed it, the spin of the other is instantly determined to be the opposite. This confused even Einstein, as information appeared to be travelling between electrons faster than the speed of light, so don’t feel guilty for being confused. Einstein refuted this idea of inherent connections between particles his whole life, calling it ‘Spooky action from a distance’ and proposed that these electrons held information within themselves that predetermined their spin states. This was experimentally disproved some years after his passing, and the phenomena is today called Quantum Entanglement, and still baffles almost everyone, and leaves me with a sore head. It does however, go some way in showing that even without a Physical connection, two things can determine each others behaviour, and offers promising real world applications, such as advancements in quantum computing.
I don’t profess to understand why these things happen, but I do believe that they’re too amazing not to share. I hope this article has somewhat sparked an interest in the Quantum World for you, as these things did for me when I first discovered them. There are countless resources on the web discussing topics like these, and they will undoubtedly explain them far better than I will ever be able to, but I thought I’d have a pop anyway.
Thanks for reading, and if you feel like it, I’ll leave you with the equation that allows you to calculate your very own wavelength! Take your mass, and your velocity (roughly 2 meters per second if you’re walking to the shop), multiply these two values together, and divide the Planck Constant (6.63×10-34) by this value, and there you have it, your very own wavelength! Do with this information what you will.
Written by Samuel Johnson.
Originally published: 1st August 2016
Updated: 15th October 2016