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Originally posted by masher:
I think this is understandable. If not, say so.

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According to Feynman and most other people involved in quantum mechanics, _no one_ really understands how it works...

As for the two-slit experiment, the reason for the interference is not photons from a different time line. The explanation is that, when you don't observe what path it takes, a photon is free to travel through all possible paths simultaneously. Most of these paths tend to cancel out, leaving just a single path that the photon travels, but in the case of the double-slit experiment, the photon interferes with itself because it travels through both slits at the same time.

Furthermore, it isn't only photons that can do this. Electrons, and even whole atoms, and theoretically anything in the world, can behave like a wave rather than a particle under the right circumstances.

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kuru
'dancing is the vertical expression of horizontal desire.'
-robert frost

quote:

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multiverse - as in the multiverse is constantly creating new universes that split off at every single instant. each universe in the multiverse grows and evolves on its own, almost completely independent from the other universes in the multiverse - so far as we know.

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This is one interpretation of the laws of quantum physics, except that each universe in the multiverse is completely independent from the other universes in the multiverse, not almost, as kuru said previously.

In this interpretation, every single way in which an event can happen, a new universe is created with it happening in each different way. For example, Schrodinger's cat. A cat is put in a box with a radioactive element, a geiger counter and a vial of poison. The geiger counter is hooked up so that when it registers a radioactive decay, it breaks to vial of poison and kills the cat. After a certain amount of time, there is a 50/50 chance that the radioavtive element has decayed, and therefore a 50/50 chance that the cat is dead. We know that if we open the box at this instant the cat has a equal chance of being alive or dead. If in our universe the cat is alive, then in the mulitverse, another universe was created with the cat dead, and vice versa.

This is know as the multiverse interpretation. In the Copenhagen interpretation, Erwin's cat is in a mixed state of being both alive and dead at the same time. This superposition of states is fixed to a certain reality when we observe the cat. The act of obervation collapses the cats wavefunction, and it becomes either dead or alive.

I think this is understandable. If not, say so.

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Remember, its all your fault.

photons.

you do an experiment in which you emit 1 photon at a time from a light source in a sealed vaccuum room. aim it at a card with 2 slits in it, and record what happens on the other side.

you get a pattern of light and dark bars recorded..... because the photons travel both like waves, and like particles, and get interference from /somewhere/.

since we know there is nothing else in the sealed room, the only place to get interference from is another universe in the multiverse.

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kuru
'dancing is the vertical expression of horizontal desire.'
-robert frost

--J

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Originally posted by Michael:
According to Feynman and most other people involved in quantum mechanics, _no one_ really understands how it works...

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Thats right. I think it was Niels Bohr who said that anyone who says that they understand quantum physics is an idiot. Or words to that effect anyway...

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Originally posted by Michael:
...when you don't observe what path it takes, a photon is free to travel through all possible paths simultaneously. Most of these paths tend to cancel out, leaving just a single path that the photon travels, but in the case of the double-slit experiment, the photon interferes with itself because it travels through both slits at the same time.

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You're right there. If we observe the photon in midflight, we just get a normal splodge of photons, no interference pattern. This is because we have broken down the wave properties of the photon and forced it to become a particle, and a particle cannot create an interference pattern. You can't say which path the photon took at all. To say which path it took requires an observation which would corrupt the experiment, as explained above.

quote:

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Originally posted by Michael:
Furthermore, it isn't only photons that can do this. Electrons, and even whole atoms, and theoretically anything in the world, can behave like a wave rather than a particle under the right circumstances.

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The wavelength of a particle is determined by its rest mass and velocity according to the de Broglie equation:

lambda=h/(m*v)

lambda is the wavelength (m)
h is Planck's constant (6.6261x10^-34 Js)
m is the mass of the object (kg)
v is the velocity of the object (ms^-1)

Here is an interesting thought experiment. You want to diffract yourself through a doorway. Diffraction is a property of waves, and occurs when the wave is incident on particles that have a spacing of the same magnitude as its wavelength.

Let us assume that the doorway is 0.7 m wide (this means that lambda needs to be about 0.7m) and our person weighs 70 kg.

l=h/(m*v)

rearranging gives

v=h/(m*l)

if we put all our numbers into this equation we get

v=6.6261x10^-34 / (70*0.7)
=6.6261x10^-34 / (49)
=1.35x10^-35 ms^-1
which is pretty goddamned slow. If we assume that we have to travel 10 cm (0.1 m) in order to pass through the door and diffract, then this will take

v=d/t
t=d/v
t=0.1/1.35x10^-35
=7.4x10^33 s

To say that is a fairly large number is an understatement. If you take the age of the universe to be 15 billion years (15x10^9 a) then the age of the universe in seconds is 4.7x10^17 s.

That means that it would take 1.6x10^16 times the age of the universe to move through the door and diffract. This is an enormous period of time.

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"All is number" - Some mathematician who's name I can't remember.

edit: i cant quote for s#!t

This message has been edited by solid on January 15, 2001 at 07:51 PM

starting PhD this year...

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"All is number" - Some mathematician who's name I can't remember.

the truth is, nobody really understands why light behaves the way it does. theories abound, but nobody can really back anything up as to what happens to particles accelerated to the speed of light, because it can't be done.

we know by observing black holes that light can behave as if it is a mass, since the gravitational field of a black hole can pull in even light. this is most commonly observed by pairs of stars that are situated relatively close together. one becomes a black hole, and we see it 'suck in' the light of the other.

all other things aside, in this instance we would have to say that light has mass, else gravity could not affect it. however, light is energy, it has no mass. so photons, those little quantized packets of energy, obviously behave like matter at some point. but why don't they weigh anything?

if they did, everything that absorbs photons (like a black cloth in the sun) would 'weigh more' as it absorbs more photons. except it doesn't. and if light were a massless wave, it would not be affected by gravity. except it is.

more over, the existence of multiple universes or a multiverse is supported by evidence in other areas. for example, black holes. we know of them as singularities. infinitely collapsing balls of matter that continue to fall in on themselves forever, becoming more and more dense. ok, that's great. except that singularity is a pretty weird concept. everything has it's opposite, up from down, light from dark, positive and negative.

so where are the white holes? where are the things that expand constantly, becoming less and less dense? theory: universes.

another one can be done with simple quadratic equations. we all did them in algebra, and we all solved ones in which the "answer" was a negative square and we were told to just 'throw that one out.' imaginary numbers are nice and all, but they don't exist. right. except that mathematics, done correctly, doesn't produce wrong answers. so negative squares exist, and they do complete that equation, somewhere. just not in our known universe. we don't know of a place where there is a number that when squared = -1. really though, higher math shows us that imaginary numbers are just another dimension of a number. that all numbers have a real and imaginary component, and that most of the numbers we deal with have '0' as their imaginary component, so we only see a one dimensional number that sits on a line.

nice, except that somewhere else, there are those numbers that don't fit on the line. the ones that must be described as a point in a plane. a two dimensional number. 2+3i, and such.

these numbers don't fit into a 3 dimensional universe, but they do fit in somewhere. another universe? maybe.

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kuru
'dancing is the vertical expression of horizontal desire.'
-robert frost

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Originally posted by solid:
1. Why do we exist
2. What's the higher goal in being here
3. Deja Vu. Why can you somewhat see the future, and why not be able to change it.

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K, you might want to take this with a grain of salt. Or maybe not. Btw this will only answer questions 1 and 2.

Although the Earth appears to have a population of approximately 6 billion the truth is the actualy number of sentient beings is unkown, but rumored to be in the region of about 100-200k or thereabouts. The unintelligeble babble and meaningless incoherency of overwhelming majority of the populace are best explained with a theory known as 'sentientism'. Essentially, the Earth is controlled by some outer-power (aliens,god, whatever) who are/is experimenting with a new species of sentient beings that they've found (that's us). We're essentially rats in a cage. This explains why so many people exhibit no signs of intelligence whatsoever (seriously, try having a conversation with some of the 'average' people in one of your classes about an intelligent subject. You'd be surprised how convincing this 'joke' theory can be). They no doubt exist soley for the reason of provoking reaction to the sentient beings that live on the Earth (similar to what our scientists do to animals, albeit on a substantially higher level) in order for the 'outer-power' to study us.

Though this may not explain the 'higher purpose' or reasons for existing outside of the sphere of our own world, it does explain a lot about how 'evolution' produced a race of six billion idiots and a few persons exhibiting intelligence. I suppose our goal would be to escape, though it seems unlikely that we'll succeed.

Maybe I should get off detnet and get back to work...

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There may be blood on the tracks, but the trains are on time.