Is it mass that bends space-time, or is it the folds in the space-time fabric that "create" mass? Which one comes first? Far from being an expert in special and general relativity, I am fascinated by the concept of time. Can we actually think of what comes first and what comes second in relativistic terms? Is there such thing as causality when we think of time as "just" another dimension? Causality is the principle that makes us say "B happens because of A". This should imply that A happens "before" B - how else could B exist? This is because in simple human terms there is only one direction in time.
Causality has already been defined in relativistic contexts, but I still can't get my head around it. If we think that time is not such a "special" dimension, but rather an "ordinary" dimension, like length or width, then saying that A happens before B is no different than saying A is to the left/right/top/bottom/in-front-of/behind B. In other words, there would be no particular meaning to the words "before" and "after", at least no more than "top" and "bottom".
Can there be no such thing as causality? Can children exist independently from their parents? Can trees exist independently from the seeds they sprouted from? Not in our everyday experience, sure, but think about it from the perspective of an entity that moves precisely at the speed of light: for example a photon.
Time is, effectively, standing still for a ray of light. Were the photon bestowed with the gifts of sight and intellect, it would "see" the world in a very interesting way. For example, let's take my current state of "being". I am currently sitting on a double-decker London bus, going to work. I hopped on the bus about 30 minutes ago and I expect to get off it in another 15-20 minutes - traffic permitting. Imagine the route this bus takes in its hour-long journey, then take a mental snapshot of this bus and imagine that snapshot filling every point of this route. The result is a very long and flexible bus-like shape that precisely traces the entire bus route. It's a bit like the starship Enterprise when it goes warp and we see it suddenly taking this elongated shape before it enters hyperspace.
Now back to our bus. Imagine tracing this bus-like shape not only through this hour-long bus route, but through all the places this bus has ever been and will be in its working life. Looks pretty messy. If a photon came into existence the moment this very bus came into existence, that's how that photon would see this bus: a messy, fuzzy, zig-zagging bus-like shape tracing a very complex pattern that goes through all the places wher this bus has ever been and where this bus will ever be in the future.
Now imagine not only this bus, but everything else, in the same way: people on the streets, buildings and trees following the rotation of the Eearth, the planets in the solar system tracing their paths, our sun tracing its path across the galaxy, and so on. That's how a photon would see the world. Nothing comes "first" or "second" or "third": everything just "is", in a big, fuzzy, dark-brown-ish mess with no concept of causality. Why dark-brown-ish? Because of innumerable objects of different colors intersecting at innumerable different points: the more different colors you mix, the more dark and brown-ish the resulting color will be.
We just said "with no concept of causality". But is that true? After all, we still know from everyday experience that children come from parents, that trees come from seeds, and so on. There must be something that relates a "cause" with an "effect". How is that going to work when time stands still? I haven't the foggiest idea, but that is a pretty good indication that, in these terms, the definition of causality must be very different from what we are used to.
Showing posts with label physics. Show all posts
Showing posts with label physics. Show all posts
23 December 2008
28 October 2008
Random Thought On The Internet
This is one of the random thoughts that usually pop right into my head when I least expect it.
I was on a work trip. One of those where you get to travel to exotic destinations but all you get to see is the office, the company cafeteria and the hotel. I was having dinner at the hotel and I started thinking of how come people have this strange need to aggregate in some area. How did people start living with other people, and how did they manage to eventually take this concept to such gigantic proportions as to create today's biggest cities, with millions and millions of individuals living close to each other.
The first reason I thought of was procreation and the continuation of the species: a certain gene pool needs a minimum degree of diversity in order to avoid extinction. Did humans in the upper palaeolithic or in the mesolithic really think along those lines? Probably not. So here I am, I'm not very good at running, hiding, or throwing spears. I can't hunt for food, but I'm good at growing legumes. If I find someone who's good at hunting, maybe we can trade food. Now, wouldn't it be easier if the two of us lived relatively close to each other instead of a half-day walking distance? I haven't studied anthropology, archaeology or any related branches, but that kind of makes sense to me.
Without going that far back in time, just think that a hundred years ago a grain of black pepper needed to travel for months to reach Europe, from south west India to Italy, but people could still find black papper in grocery shops, because they lived in human settlements where specialisation of roles could support a complex social infrastructure: different people can do different things and provide different needs, but they need to be in relatively close proximity in order to maximise their reciprocal advantage.
In physics, this is equivalent to a system trying to find its equilibrium by minimising its energy. An electron in an excited atom "prefers" to drop to a lower energy level if that level is not already full. This is what the electron thinks: what's the point in doing so much work just to keep running like mad in a "higher orbit", when I could just cruise casually around a "lower orbit"? So the electron "drops down" an energy level and sheds the excess energy in a flash of light. And no, I haven't studied much physics either, but that kind of makes sense to me.
Extrapolating the principle of minimising a system's energy, here's what a human might think instead: what's the point in spending half a day travelling to buy some food, load up enough food to last me a while (because it's not like I'll do this again tomorrow, or the day after), then carry all that food back home and manage its storage, when I could just move downtown and simply pop down to the corner shop whenever I need to?
The real achievement in moving downtown, in really fancy terms, is not that I have found a low-energy equilibrium. My half-day walk has become a two-minute stroll. The 20 kilometers between the shop and my house have become less than 100 metres. By moving downtown I have effectively compressed space and time.
Today, as a human living in the remote countryside, I don't actually need to move at all, but I can still compress space and time. How? With Internet, of course. I don't need to live in relatively close proximity to other humans and human structures: I need to move to wherever there is an Internet connection and a postal service, and these might well exist in the remote countryside as well as downtown. So will internet reverse the process of urbanisation, or at least will it make such reversal possible? I think so. Virtual offices, internet videoconferencing, voice-over-IP, news streaming, bla bla bla... it's all there already. The recent hype of "going green" even encourages to great extents to stay where you are, avoid travelling, avoid lighting up an entire office or unnecessarily loading the public transport system if you can work from home. The fascination for "going downtown", perhaps, will eventually be confined only to touristic attractions. I'm not saying people will have no more reasons for sticking together in organised physical conglomerates: I'm just saying, IMHO, that there will be a lot less of a motivation to do so in the future.
M.
I was on a work trip. One of those where you get to travel to exotic destinations but all you get to see is the office, the company cafeteria and the hotel. I was having dinner at the hotel and I started thinking of how come people have this strange need to aggregate in some area. How did people start living with other people, and how did they manage to eventually take this concept to such gigantic proportions as to create today's biggest cities, with millions and millions of individuals living close to each other.
The first reason I thought of was procreation and the continuation of the species: a certain gene pool needs a minimum degree of diversity in order to avoid extinction. Did humans in the upper palaeolithic or in the mesolithic really think along those lines? Probably not. So here I am, I'm not very good at running, hiding, or throwing spears. I can't hunt for food, but I'm good at growing legumes. If I find someone who's good at hunting, maybe we can trade food. Now, wouldn't it be easier if the two of us lived relatively close to each other instead of a half-day walking distance? I haven't studied anthropology, archaeology or any related branches, but that kind of makes sense to me.
Without going that far back in time, just think that a hundred years ago a grain of black pepper needed to travel for months to reach Europe, from south west India to Italy, but people could still find black papper in grocery shops, because they lived in human settlements where specialisation of roles could support a complex social infrastructure: different people can do different things and provide different needs, but they need to be in relatively close proximity in order to maximise their reciprocal advantage.
In physics, this is equivalent to a system trying to find its equilibrium by minimising its energy. An electron in an excited atom "prefers" to drop to a lower energy level if that level is not already full. This is what the electron thinks: what's the point in doing so much work just to keep running like mad in a "higher orbit", when I could just cruise casually around a "lower orbit"? So the electron "drops down" an energy level and sheds the excess energy in a flash of light. And no, I haven't studied much physics either, but that kind of makes sense to me.
Extrapolating the principle of minimising a system's energy, here's what a human might think instead: what's the point in spending half a day travelling to buy some food, load up enough food to last me a while (because it's not like I'll do this again tomorrow, or the day after), then carry all that food back home and manage its storage, when I could just move downtown and simply pop down to the corner shop whenever I need to?
The real achievement in moving downtown, in really fancy terms, is not that I have found a low-energy equilibrium. My half-day walk has become a two-minute stroll. The 20 kilometers between the shop and my house have become less than 100 metres. By moving downtown I have effectively compressed space and time.
Today, as a human living in the remote countryside, I don't actually need to move at all, but I can still compress space and time. How? With Internet, of course. I don't need to live in relatively close proximity to other humans and human structures: I need to move to wherever there is an Internet connection and a postal service, and these might well exist in the remote countryside as well as downtown. So will internet reverse the process of urbanisation, or at least will it make such reversal possible? I think so. Virtual offices, internet videoconferencing, voice-over-IP, news streaming, bla bla bla... it's all there already. The recent hype of "going green" even encourages to great extents to stay where you are, avoid travelling, avoid lighting up an entire office or unnecessarily loading the public transport system if you can work from home. The fascination for "going downtown", perhaps, will eventually be confined only to touristic attractions. I'm not saying people will have no more reasons for sticking together in organised physical conglomerates: I'm just saying, IMHO, that there will be a lot less of a motivation to do so in the future.
M.
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