I am a big fan of a TV show called Doctor Who, I’m sure a lot of you will know it too, but for those of you that don’t, don’t leave yet! The show revolves around a character called The Doctor who travels through space and time in a craft called the Tardis. Every time someone new enters the Tardis, they notice something. From the outside, the Tardis takes the form of a circa 1954 police box, but once you go inside it is much bigger! Even for those of you that do not watch the show, there is some interesting physics that could explain this behavior, so stick around! Firstly, let me give you two images so you can compare the outside to the inside:
As you can see, there is quite a distinction. So, lets start with the most simple way this could work. The interior of the Tardis is in a set location, it doesn’t move. The exterior acts as a portal. As someone steps into the phone box, they are teleported across the universe. This sounds a little far fetched, but it is, in theory, possible, by two methods. We have all seen teleportation in movies or tv shows before, someone stands in a machine of some sort and disappears only to appear immediately in another location. I always assumed this was the producers using a bit of artistic license, but there is a way it could work. The machine would have to observe every particle in your body, change it into a series of binary digits, send that to your destination where it would have to be decoded and then you would have to be rebuilt.
However, here are three main problems with this, the signal could only ever travel at the speed of light. Using this to teleport to really far parts of the universe would not work as it would take so long for the signal to reach it. Secondly, there is a moral issue, if you are reconstructing someone somewhere else, can you just kill the original? Are they considered to be different people, or the same? They would both identify themselves as the same person and believe themselves to be the real one. Anyway, this is an ongoing debate, and as much as I enjoy it, we aren’t here to talk philosophy. Finally, and perhaps the biggest problem, the that within the human body, there are roughly 7,000,000,000,000,000,000,000 atoms. If we could give one binary digit to each, that is about 8,100,000,000 gigabytes. At out highest download speeds, this would take around 300,000,000,000 hours to download, 30,000,000 years! But even then, you can’t represent an atom with one bit of information, so it would be much more data than that. In other words, until our computer technology is much better than it currently is, we have no chance of getting this to work. Though, we have managed to teleport particles!
The other method it could be using is a wormhole. The wormhole starts at the entrance of the exterior, and takes a shortcut through spacetime and to the interior. When the Tardis moves, all that is changing is the entrance to the wormhole, and seeing as The Doctor’s race, the Timelords, were incredibly technologically advanced, it doesn’t sound that unrealistic.
The next way the Tardis could be made to seem bigger is if the people entering were made to take up less spacetime, in other words, they are shrunk. Unlike if we were thinking in a classical way, when looking at this situation, we have to think of every person as a collection of atoms. How do we shrink them then? You either remove atoms or you decrease the distance between them. There are problems with both of these: removing atoms could be very troublesome, our bodies work perfectly due to some pretty exact chemistry. Changing concentrations of things and removing atoms could create large knock on effects to the whole body. Decreasing the distance between atoms is even more troublesome. In solids, it is pretty much impossible due to repelling force felt by the two atoms. In liquids and gases, this can change physical properties like viscosity (how runny a substance is) which the body may not be suited to. So if making the person fill less spacetime isn’t possible, how about we reverse it? They have more space-time to fill. This is a weird concept, we have talked about spacetime before and I am going to use a similar analogy. Imagine a sheet of rubber. This is spacetime. Now, for the Tardis, what could have been done is that it takes the rubber and stretches it. This leads to one section where the Tardis that has a large area but fits onto a small place on the sheet, in other words, the “bigger on the inside” effect we see in the Tardis. However, there is a problem with this. To have this sort of thing, spacetime has to be distorted greatly. What to we get when we have twisted and distorted spacetime? We get gravity! In fact, the tardis interior is really big, and the gravity would be so high, it could create a black hole! Update: I have been informed that the power source of the Tardis has been said to be the Eye of Harmony. Interestingly, the Eye of Harmony is a black hole and could make this theory much more likely!
Ok, now we come to the last and the most likely of the three. In fact, this mechanic is implied The Doctor at points. He has said before that the Tardis is “Dimensionally transcendental”. the long words are no doubt there to make it sound very complicated, and very complicated it is! The idea is that the inside of the Tardis is inside the exterior and in fact fits in exactly the same three-dimensional space. However, it expands into higher dimensions, making its volume large. Imagine a piece of paper with the base of the Tardis drawn on and then an extra piece of paper attached to one side of that box, perpendicular to the original base. All the people are 2D in this space, but once they enter the Tardis, they can go onto that third dimension, making the space much larger that it appears from an outsider living in only three dimensions.
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