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interesting physics

Posted on 2009-12-19
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Hi

I rencently posted a question about issues in science that might interest bored teenagers. One of the answers was quantum physics and I think this is a great idea. Some of the things mentioned were

1) time travel
2) parallel universes
3) fate of the universe

Are there any other 'main' issues in quantum physics. If anyone could provide a sentence or two about each of the above points it would be much appreciated. I need to know by Monday really. I have tried to look into this but the explanations are too much for me to get to grips with in the limited amount of time. I just need a 'soundbyte' until i can look into it further

thanks
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Question by:andieje
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ozo earned 800 total points
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quantum gravity
renormalization
quantum computing
Copenhagen vs Many worlds vs objective collapse vs Bohm vs Penrose vs Stochastic vs Transactional vs  ...
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by:aburr
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1) time travel
causality and time travel is the most important consideration here. If one travels to the past can one change the present?
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2) parallel universes
How to prove their existence? Indeed parallel universes miaght be the answer to the causaity problem of time travel.
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3) fate of the universe
This may not be the most interesting of the topics but it is clearly the most teachable and has the greatest possibility to provide real science instruction, rather than uninformed speculation.
The universe can collapse, it could be exploding (expanding indefinitely), or in some steady state. Gravity, Hubble constant, microwave background all have connections with this topic.
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The trouble with "interesting topics" is that people in general do not want to learn the basic principles necessary to understand them. It is difficult to keep discussions under control and to prevent them degenerating into opinions, all of which are just as good as any other. They can be used as an introduction into the nature of proof, the possibity of falseification, and how scientific consensus is reached.
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by:ozo
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> causality and time travel is the most important consideration here. If one travels to the past can one change the present?
In a classical model of time ravel, say you had a billiards table with a time travel portal and you set up a shot so that
the ball enters the portal, travels into the past and deflects the incoming ball so that it does not enter the portal, causing a contradiction.
It can be shown classically that there will always exist a non-contradictory path with the same initial conditions,
e.g. the ball emerges from the portal at a slightly different angle and deflects the incoming ball just enough so that it enters at angle consistent with the way it emerges.

I'm not sure about the quantum case, but I think I heard of an analysis suggesting that a consistent solution must also exist in a quantum model.

perhaps CPC can be altered so that feedback only destroys inconsistent closed time-like loops...
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by:InteractiveMind
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As this stuff will be aimed at children, I don't think it's worth getting into time-like loops, renormalisation, etc. Definitely stick with some soundbytes:

One upon a time, we knew nothing about the universe. But we've since managed to encapsulate the future of the entire universe in just two fairly simple-looking equations!! (The Friedmann equations) If that doesn't send a shiver up anyone's spine, then I don't know what will. (Cosmology)

The existence of parallel universes was not introduced by scientists in order to solve a problem, but instead was actually predicted by theory! (Parallel U)

Electricity and magnetism are just two different faces of the same coin! (Electromagnetism)

Particles can be in multiple locations at once! (QM)

Two particles can be taken to opposite ends of the universe, and still communicate with each other *instantaneously*! (EPR paradox)

Explain the 'three polarizer paradox'. (QM)

I also recommend watching this ~80min talk between Steven Weinberg and Richard Dawkins:
http://www.youtube.com/watch?v=edsDrqfDVKY
Weinberg explains the current state of theoretical physics.

Have to go now (my laptop battery is virtually dead), I'll try post some more before tomorrow.
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by:InteractiveMind
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In fact, kids love paradoxes perhaps more than adults, and there are lots in science:
http://en.wikipedia.org/wiki/List_of_paradoxes
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by:ozo
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> Two particles can be taken to opposite ends of the universe, and still communicate with each other *instantaneously*! (EPR paradox)
I think that description stretches the notion of "communicate" in a way that could be misleading to adults, much less children.

I think one of the best people for explaining such mind bending concepts in a way mere mortals can grasp was Richard Feynman
some of his lectures are online here
http://research.microsoft.com/apps/tools/tuva/#data=3
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by:ozo
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> Electricity and magnetism are just two different faces of the same coin!
you can think of magnetic fields as a relativistic transform of electric fields
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by:stsanz
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- Teleportation

It can be linked to quantum physics subject of entanglement.
http://en.wikipedia.org/wiki/Quantum_entanglement

- How many technological objects work

For exemple : GPS (subjects of triangulation, relativity), CD player (laser), ...

Who doesn't know the great site:
http://www.howstuffworks.com/

and its wonderful explaination of how GPS works:
http://electronics.howstuffworks.com/gadgets/travel/gps.htm
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by:tliotta
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I often like the simple stuff -- "What does the surface of a proton look like?"

Does 'surface' have any meaning there? At that scale, how would the wavelengths of light affect the question? How could "seeing" work at all? If 'surface' has any meaning, what is the 'stuff' like? What does the 'stuff' look like as the proton is converted to energy?

Almost any 'simple' question immediately leads to serious difficulty. Much of it has to do with the time- and distance-scales that we live our lives within. As those scales are examined in their extremes, our perceptions may be shown to be misleading.

Tom
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by:stsanz
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"What does the surface of a proton look like?"

The question is meaningless, since the proton is NOT a sphere or a ball. Classical graphic representation of particles as balls fool us about this.

A proton is made of three quarks maintained together by strong nuclear force. In the state of today's physics, a quark can only be described as a point (surfaceless and volumeless) with properties associated.

Maybe one day, our knowing of elementary particles will let us gain a more concrete representation of a particle.
But while going deeper and deeper into knowing the intimate nature of matter, my conviction is that physics is compelled to finally describe the unvierse only with mathematical concepts, rather than physical concepts. Could is be that the intimate nature of the universe is mathematic ? Why not ?
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by:ozo
ID: 26103488
"What does the surface of a proton look like?"
If this is a question about how protons interact with photons,
I think there would be little interaction with visible light photons.
but with higher energy photons you would have Compton scattering.
If it is a question about how we can visualize the properties of a proton,
that can get much trickier.
We tend to visualize based on familiar objects with familiar properties,
Some of a proton's properties may have no familiar analogue,
and while you may be able to construct a an analogue for some
properties based on familiar concepts, the analogue you construct
may depend on which properties you want to depict.

I'm not sure I understand the distinction being made here between mathematical concepts, and physical concepts
 
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by:ozo
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Is this a question specifically about quantum physics, or any physics?
Would you prefer physics that students can observe themselves?
What about trying to see Haidinger's brush?
Constructing a device to protect an egg when dropped?
Dropping a tennis ball on top of a basket ball?

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by:stsanz
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> We tend to visualize based on familiar objects with familiar properties,

Yes, but during history of science, making analogies with familiar concepts has often proven to be misleading and source of misinterpretation. The Greeks thought matter was made of 4 elements that had a true existence : it was wrong. Viruses were first depicted as small insects : it was wrong. The void space was first assimilated to a concrete matter known as "ether" : it was wrong. And more recently, subatomical particles were modelized as spheres : wrong again.

My opinion is that physics have come to the stage where it is not possible anymore to make analogies with familiar concepts without misleading science. Refer in quantum physics, to wave-particle duality, entanglement, which we cannot explain because they go against our familiar concepts.

> I'm not sure I understand the distinction being made here between mathematical concepts, and physical concepts.

Well, your distinction between familiar objects and non-familiar objects is similar. A sphere or ball is what I call a physical concept because it can be materialized with a concrete and familiar object having the same properties. This is not possible with the mathematical concept of "point".

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by:ozo
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> making analogies with familiar concepts has often proven to be misleading
Thus the difficulty with visualizing unfamiliar objects like protons.
Even in classical physics, physical intuition about familiar objects can be misleading.
Before Galileo and Newton, people had some strange ideas about how familiar objects behave.
Beginning students often still do.
But physical intuition can be trained.
It is possible to develop a more correct intuition about classical physics than naive intuitions.
And I think it is also possible to develop some intuition into some aspects of quantum or relativistic physics.
Such physical intuition can be useful to guide your exploration of the mathematics.
It can be possible to solve problems with just the maths an no physical intuition,
but just the maths without familiarity with the physics, one might take the math
in aimless directions without knowing whether one is closer to a solution,
or to find a solution and have no idea how it relates to the physical world,
(or to make mistakes and not catch it when you don't realize your equations are describing physical nonsense)

I don't know that a perfect physical sphere exists any more than a perfect physical point.
and physical balls have so many properties that I doubt one can say one is more familiar
with all of its properties than one is of the properties of a point.
(and some models of quantum gravity do try to build physical spacetime out of conceptual points)

Protons and photons do seem to have a physical existence.
although they can also be thought of as just ways of describing some terms in some equations.
It maybe trickier to ask whether virtual photons are physical or mathematical.
The equations which describe them do have real physical consequences.,
But there are also other ways to write the equations so you split out the terms out in different ways.
Then again, that might also be said for equations describing physical balls.
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by:tliotta
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IMO, the latest comments begin to illustrate what I was getting at.

The whole idea of "simple questions" collapses dramatically when examined closely. Isn't that a major point of education? If things were actually simple, we'd graduate from 6th grade rather than needing to continue through college and beyond.

By having a group of young minds attempt to grapple with the very real problems presented by sub-atomic or cosmic scales, some of the mystery might spark interest.

To young minds (ignoring older minds!), saying "The question is meaningless, since the proton is NOT a sphere or a ball." is itself meaningless, as is "A proton is made of three quarks maintained together by strong nuclear force. In the state of today's physics, a quark can only be described as a point (surfaceless and volumeless) with properties associated."

How can you begin to talk to young minds with terms such as "a point (surfaceless and volumeless) with properties associated"? How can you expect any sense to be made out of it? I suspect that that's one of the failings of teaching methods.

A "point" is in itself non-sensical. It can neither be sensed nor described. To go that route directly is to guarantee a large drop-out rate and to foster disinterest.

OTOH, to guide youth along a direction of seeking the answer to a "simple question" should foster interest.

Take a magnifying lens and examine why it makes things look bigger. Okay, then let's compound the lenses and work on focusing to get greater magnification. Is that good enough? No? Why not? Can we simply make more powerful lenses? Yes. Are they good enough? Why not? Can you use different equipment? What kind? Is it good enough? Why not?

Along the way, an awful lot of fundamental general physics can be examined, one step at a time. Each step may be understood in terms of the previous one. Some of the nature of light begins to be grasped simply by repetition at each step and by experience and experiment.

Ideally, the conclusions about the meaninglessness of the original "simple question" should be reached naturally. It should be a personal discovery rather than being confronted by a similarly meaningless pronouncement. Without some experience, the pronouncement cannot carry meaning across.

Just my opinion, but I believe it's a far better approach for those just recently out of grade school or middle school.

Tom

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by:andieje
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I have not forgotten this question. It's quite interesting some of the points raised and I think i agree with tom but i need to read it in more detail.
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by:tliotta
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> I think i agree with tom...

I'm not sure that "I" agree with me (tom). I don't participate because I always (ever?) know the answer, but rather to learn. I would be completely happy if someone responded to my stance with an explanation that I understood. I'd _love_ to learn that kids in general could and would accept discussions on the order of what's been presented above.

There will always be the rare ones who will. I don't think we're talking about them here, though, and I don't think they need to handled in the same way.

For a basic group beginning high school level or early in it, I don't yet see much alternative.

Tom
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by:andieje
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They just don't find science interesting. I didn't when I was younger either. I think it's because when you study science, even as a child, you know that what you are being taught is a huge oversimplification of what's really happening that you can't even begin to conceptualise yourself at a point where you could understand the reality. This makes science seem irrelevant. It seems a million miles away and too unachievable. That's how I saw it as a child anyway. I was told that children identify with science more when they can imagine it being done by real people. So for example, the can identify with the races and (national) battles to be the first to discover something scientific because they experience competion and patriotism in their own lives. Things like this help to make science more real.
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