Teh:
a photon, or for that matter any particle, travelling west-to-east is like a finger dipped in a puddle?
If we are trying to understand the behaviour of light this question is not useful. This is because it purports to be about an event happening in the real world but it does not relate to any observations of that world. For the purposes of everyday life, and in fact for most scientific purposes, this doesn't matter because for both of these purposes we usually make the approximation that an act of observation has no effect on the thing being observed. It
is an approximation. It is never strictly true. But, for most purposes; for most accuracy requirements, it works fine. But when dealing with small sensitive things like photons or electrons, it matters a lot. In this case, we have to make sure we talk about what is observed. Then we can dream up models to link and predict those observations. It does not help us in any way to speculate about what is happening between the observations, unless we are proposing to insert another observation there.
In the case of the electron and the twin slit experiment, what is observed is a load of dots on a screen. When we reduce the voltage in the electron gun, we notice the density of dots decreases. And vice versa. This looks a bit like what we see if we do the same thing with bullets, or other small relatively discrete chunks of matter. We label this class of observations with the word "particle".
But here is another observation: when we look at the pattern of dots we see interference fringes. This looks a bit like what we see if we do the experiment with a tank of water or some vibrating air. This is a class of observations to which we attach the word "wave".
This is the meaning of wave-particle duality. The word "particle" is a model that describes a particular set of observations. The word "wave" is another model of other observations. The set of observations that we associate with the word "electron" (or "photon") contains some members that are in the "wave" set and some that are in the "particle" set.
The wave nature of the electron is often regarded as representing the probability of making a particle-like observation at a particular point. The consequences of that way of looking at it seem to fit pretty well with many observations.
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It is a similar situation with photons. Some of the observations associated with what we call "light" (or, more generaly, electromagnetism) fit in the "wave" set. (Have you ever seen a rainbow?). And some fit in the particle set. (Have you heard of the photoelectric effect?) But, in this case, the interpration of the wave as representing the probability of making a particle observation is not a good fit to observed evidence. For a good description of the observed behaviour of light you need quantum field theory. Ultimately, to tie both together in one framework a thing called "gauge theory" is useful. Or so I hear.
But the principle of wave-particle duality, as explained above, is the same.
I think you need to appreciate the difference between a particle and a wave.
You need to appreciate the difference between a set of observations and models created to describe those observations. Statements like: "A photon
is a particle" or "A photon
is is wave" are not helpful to an understanding of the observed nature of light. The only thing that you can truly say about what a photon
is is this: "A photon is a photon". Anything else is either a partial description of some of its properties (i.e. only a subset of all the observations collectively known as "photon") or is a way of categorizing it (i.e. places all of the observations corresponding to the word "photon" into a super-set.) eg: "a photon is
an example of a gauge boson".
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Gene16180:
I dont know; but the people who are wrong in this debate are those who claim that they do.
Supine:
This sounds like theological polemics to me.
To be honest, I really don't see how you can interpret an admission of ignorance as a theological polemic!
Supine:
99% of what I learn in science I take as truth through faith.
Is this because you are told it by others but don't have the time or the resources to confirm it first-hand? If this what you mean, then we take almost everything we know on faith. I take it on faith that a country called Australia exists. I can't afford the air fare to find out for myself. But it is clear that I could, in principle, confirm its existence for myself. The people who
have been there have described experiments that I could, in principle, do to find out for myself (although they wouldn't put it in those terms). Likewise with scientific truths.
so science has its limitation.
Absolutely true. As does all indirectly aquired knowledge.
I'm still trying to wrap my head around the idea how the earth pushes away as my foot pushes off of it.
Picture yourself in a boat on a river.
There is another boat right next to you. Give it a kick. What happens? Both boats, yours and the other one, move away from each other. Now picture the other boat a little bit bigger. And bigger. And bigger. It will move less and less. But there is no point where it will suddenly go from moving a little bit to being
completely unmoved.
The Earth is a
huge boat.
Every beat of your heart makes the Earth move a little bit.
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Ktulu:
I think you are being too lenient...
I was not trying to say that things like psychic experiences should be studied using the scientific method (although I was not actually denying it!). I was just saying that many, probably most, people do not regard the scientific method as the only form of understanding.
I agree that the thing we formalize as "science" appears to be wired into our brains. We do it all the time. We work things out and make predictions based on past experience. But there are other modes of thinking that are not interested in working out how the world is going to behave based on patterns in past experience. I'd just like to give those modes of thinking their due respect and be careful not to imply that they have no worth, simply because the scientific mode of thinking is so successful at what it does.
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Teh:
In the Copenhagen interpretation, there is no objective collapse of the wavefunction, because there never was a wavefunction in the first place.
In the same sense, there is no such thing as gravity. Just stuff falling towards other stuff. There is no such thing as an electron, just a load of observations of dots on screens, light bulbs shining, objects being resistive to the touch, and so on.
The wavefunction is part of a model to describe observations. In this sense, it exists.
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Quotidian:
The wave function is after all a probability wave, not a physical wave like one you ride on a board.
Even the physical wave on the ocean is only approximately described by wave equations. Models, like wave equations, are always inexact approximations. If they were not, then they would not be models. So I think there is a sense in which you can say that both types of waves are the same: descriptions of some,
but not all, possible observations of the phenomena that they purport to represent.
It is just the probability of finding the particle, so called, in a given range at a given time.
That is a useful way to see it, yes.
But the particle, so called, is not anywhere in particular until you measure it.
I would say it like this: The statistical distribution of the set of observations that can be closely modelled by the "particle" concept can be modelled by the "wave" concept. It may seem odd that this wave can usefully be regarded as passing through both slits in the double-slit experiment. But "passing through" means "moving" and "moving" means changing position with respect to time. And the wave equation is time dependant. (The "Time dependant Schrodinger Equation".) Looked at in the right way, it's not really much stranger than the idea of a water wave passing through a gap. What is a water wave? It's not a piece of matter. That's just the medium. It is a representation of a time-dependant spatial configuration of lots of pieces of matter. Of course, we use the word "energy" and then have the sense that "something" is moving through the gap. But what is energy if not an abstract concept invented to describe... etc.
The Copenhagen Interpretation gives back some of what the Enlightenment took away, by placing the act of observation at the centre of reality itself. This is one of the reasons that it has become the basis for a whole new spiritual movement.
Which is, I think, yet another cautionary tale about the dangers of extrapolating from some, but not all, aspects of a description to a prescription or value judgement.
- By tonylang
- By iamstephanieejike
- By Sy Borg