“In the quantum theory of gravity, time becomes the fourth dimension to add to the three dimensions of space (x, y, z or length, width and height), and Stephen Hawking has suggested that we consider it analogous to a sphere. Developing this analogy, we imagine time to be like a flea running around on the surface of a ping-pong ball. A continuous journey, without a beginning or an end. The ‘big bang’, frequently discussed as the beginning of everything, and the ‘big crunch’, proposed by physicists as how things will end, would be the north and south poles of the sphere. The Universe would simply exist. The radius of circles of constant distance from the poles (what we might call lines of latitude) would represent the size of the Universe. Quantum theory also requires the existence of many possible time histories of which we inhabit one. Different lines of longitude can represent these histories.
If you are not already lost (the analogy does not include a useful compass) then physicists would give you a final spin by dropping in the concept of imaginary time! Maybe it is time for the flea to jump off the ping-pong ball, but before it does, we can appreciate that it might move in one direction and then retrace its steps (or its hops if you wish to be pedantic). The flea can travel backwards because in this concept of the Universe, time has the same properties as the other dimensions of length, height and width and so it has backwards as well as forwards directions.”
This is an extract from a book called ‘The Entropy Vector: Connecting Science and Business‘ that I wrote sometime ago with Bob Handscombe. I have reproduced it here in response to questions from a number of learners in my current MOOC. The questions were initially about whether the first law of thermodynamics has implications for the universe as a closed system (i.e. one that can exchange energy but not matter with its surroundings) or as an isolated system (i.e. one that can exchange neither energy not matter with its surroundings). These questions revolve around our understanding of the universe, which I have taken to be everything in the time and space domain, and the first law implies that the energy content of the universe is constant. The expansion of the universe implies that the average energy density of the universe is getting lower, though it is not uniformly otherwise we would have reached the ‘cosmic heat death’ that I have discussed before. However, this discussion in the MOOC led to questions about what happened to the first law of thermodynamics prior to the Big Bang, which I deflected as being beyond the scope of a MOOC on Energy! Thermodynamics in Everyday Life. However, I think it deserves an answer, which is why reproduced the extract above.
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… I don’t know a diplomatic way to put this, so I usually just say nothing, but time and space are not disconnected not analogous to each other.
Time-space is a useful concept, but just because we can say a lot about something, like whether Han Solo shot first or not, doesn’t mean that it is very useful to do so.
We can say more about the universe if we look at it as a set of parts, but it is not really so… the consciousness of humans, and our ability to do both stupid and creative, original things informs how both time and space can be enhanced, sometimes by our very attitude of being, before any physical or apparent work is done.
Spacetime, time-space, when and where, are all useful… but decomposition might not be, unless we want to waste our time and ignore our environs.
Hey, I’m sorry about being so caustic. I should have found a diplomatic ways to say what was on my mind.
When I reflected on it, I don’t know why I was so annoyed about it… it doesn’t take anything away from me, and I myself recently used the concept of the imaginary plane to help explain some types of things, although I haven’t given the model the rigorous testing that I would like, so it is, at this point, even really more of a useless thing than anything in physics could be.
So, I’ll try again… although I personally find models useful, I don’t agree with making time analogous to space. I also find that the word “dimension” has too many meanings, and I think that confusing arises which leads to mistakes in models, or confusion for non-physicists. However, I don’t have a solution in words alone.
If I teach, I always use diagrams and specific words, and a little story to explain the dis-ambiguity, but that all takes a lot of time and effort, and part of why humans can be trapped into bad habits is that compression of concepts into mantras which are based on mistakes can combine with other mistakes, and create a blind spot which makes the mistake invisible.
Perhaps I took out my frustration at how much pain it causes me, dealing with people who aren’t open to deep discussion, yet control resources which humanity needs for progress, in my previous post… and also frustration at not being able to express my own view in a few words. So, sorry about that.
I’ll have to bit the bullet and work on a short booklet about what I was talking about, sometime.
Mate… this is good stuff, I love it. I see things you cannot. You are me, I am you… we are the same but different .
Thanks for making me think, you have a good mind.
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