I’m going to confuse my readers by making my first proper post something I never really did on any of my blogs beforehand: a three-part science post! I know I have a few science fans here, and I’m going to pull together a few of the things I find the most interesting: time-travel, quantum mechanics and extra dimensions. Ooh, you’re excited now, I can tell.
And as you always should with a post like this, I’m going to start with Richard Feynman. Richard Feynman postulated that there could be only one electron in all of existence. His explanation of why there looked to be billions upon billions of electrons was that the one electron that did exist travelled through time. Image, if you will, that all of the Dr Who personalities all took their TARDIS to your living room, now. It would look like there were dozens of Dr Whos and TARDISs, when we all know there is only one. The illusion of many is from the fact that they have all come from different points in time.
In principle this is what Feynman said a single electron could be doing*. The single electron could be going through quantum-sized wormholes, and reappearing at times it already existed and thus existing alongside a younger version of itself. Quantum-sized wormholes are another possibility in our understanding of the universe at it stands. I don’t understand the mathematics that underpins this theory, but the theory is robust (it’s in The Grand Design by Hawking and Mlodinow).
*Feynman never said that this is what is happening; merely that it is a mathematical and conceptual possibility. If you like, he was simply having fun with concepts.
It’s not just wormholes that can explain how one electron can time-travel. All quantum particles have the possibility of travelling backwards through time. But an electron travelling backward doesn’t look like an electron travelling backwards; it looks like a different particle—a positron—travelling forwards. This is where we need to get graphical, so consider the graph below.
The zagged line, composed of both blue and red, represents an electron The blue line is when the electron is travelling forwards in time and looks like an electron. The red line is when the electron is travelling backwards through time and looks like a positron. The vertical axis represents time. As an observer you cannot help but travel in only one direction: up the graph. Because you cannot choose to travel down the graph (i.e. backwards in time) everything you see appears to be travelling in the same direction through time. The five horizontal grey lines represent certain moments you can observe. Those moments in order are as follows:
At moment 1 you are looking at one electron travelling forwards in time.
At moment 1.5 you are looking at the same electron you are looking at in moment 1, as well as what appears to be two particles appearing out of nowhere. These two particles look like and electron (the blue line) and a positron (the red line). In reality, you are looking at the moment an electron stops travelling backwards and starts travelling forwards; a junction as the electron changes direction.
At moment 2 you are looking at what appears to be three different particles: two electrons and a positron. In reality you are looking at one electron at three different stages in its journey through time.
At moment 2.5 it appears you are looking at the electron you saw in moment 1 and the positron you saw in moment 2 crashing into each other and annihilating to nothing, plus another electron. But you are actually looking at the moment that the electron stopped travelling forwards in time and started travelling backwards.
At moment 3 it appears you are looking at an electron different from the electron that you saw in moment 1. In reality, you are looking at the same electron.
If you’re lost, and on your first reading you probably will be, take a moment with the summary graphs below:
On these graphs I have gotten rid of the “moments”, but I have added directions of motion through time. These are the little black arrows. Graph 1 explains what appears to be true, which is that it appears that all three things travel in one direction: up the graph. This is all the things travelling forwards in time. Because we can only travel forwards in time it will always look like things are travelling forwards in time. As a result it looks like three different particles that appear from nowhere and disappear to nothing. Graph 2 shows what it is Feynman speculated: that those three particles are actually one particle that travel through time in a weird way. As a result there are times where it looks like there are three particles even though there is only one. The direction arrows show this is one particles in continuous motion.