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On March 17 2010 05:53 starfries wrote:
If it's unobserved then there is a range of places where it could be, like a probability distribution. Pretty reasonable... but the weird thing that quantum mechanics says that it doesn't just exist somewhere within the distribution, but it actually exists EVERYWHERE to some extent. It's spread out over space, just like a wave. (it's not exactly like this but its close enough) This means it can interfere with itself, etc. It doesn't just happen for light either, it works with electrons, protons.. technically it should even happen when you walk through a door but the wavelength involved is so tiny that you'll never see it.
When you observe a particle (or detect which slit it goes through), you force it to have a definite position so suddenly the probability distribution collapses down to a point. It's like flipping a coin - when it's in the air, it has probably H with 50% and probability T with 50%, but after you catch it and look at it, it's one or the other with 100% probability. Since the distribution is basically one point now, it behaves like a particle again.
But what if some amoeba was just eyeballing that particle the whole time and we never found out?
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On March 17 2010 06:22 spitball wrote:Show nested quote +On March 17 2010 05:53 starfries wrote:
If it's unobserved then there is a range of places where it could be, like a probability distribution. Pretty reasonable... but the weird thing that quantum mechanics says that it doesn't just exist somewhere within the distribution, but it actually exists EVERYWHERE to some extent. It's spread out over space, just like a wave. (it's not exactly like this but its close enough) This means it can interfere with itself, etc. It doesn't just happen for light either, it works with electrons, protons.. technically it should even happen when you walk through a door but the wavelength involved is so tiny that you'll never see it.
When you observe a particle (or detect which slit it goes through), you force it to have a definite position so suddenly the probability distribution collapses down to a point. It's like flipping a coin - when it's in the air, it has probably H with 50% and probability T with 50%, but after you catch it and look at it, it's one or the other with 100% probability. Since the distribution is basically one point now, it behaves like a particle again. But what if some amoeba was just eyeballing that particle the whole time and we never found out?
The short answer is:
Observation is actually not a good word for this sort of stuff, and what we really are talking about is measurement. The modern interpretation is that "measurement" is a forced decoherence of the quantum state by a macroscopic system, and an amoeba is a macroscopic system so it will cause the collapse of the wavefunction before it enters the slits. So you will see particle behaviour, as if you measured it yourself.
Ok that was actually not that short of an answer but the long answer is a LOT longer.
short short answer: the amoeba counts as an observer, it behaves as a particle
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On March 17 2010 04:28 decafchicken wrote:Show nested quote +On March 15 2010 01:53 SpiritoftheTunA wrote:On March 15 2010 01:49 Housemd wrote:
This is interesting due to the fact that i having a conversation about it in class today with my math teacher.
HE says that the reason we can't travel the speed of light is due to the fact that this happens:
When we shoot a particle of light into a spectrum (or something, not quite sure) on the other end, the particle turns out to be TWO particles, each in a different location on some black paper they put as a "receiver". If we can find out what causes this, we can travel the speed of light to different galaxies. I think you're talking about this. http://en.wikipedia.org/wiki/Double-slit_experimentThis is an experiment that demonstrates the wave-particle duality of light. If you shoot a photon of light through two slits, and don't detect which slit it goes through, then the photon will act as if it went through both slits (even though it technically should be only one particle) and interfered with itself (as if it were a wave). This has to do with quantum mechanics, which I highly suggest you should learn in your academic future! To be honest, it doesn't have that much to do with the speed of light itself, but it's one of the things that got me interested in physics, so by all means, be open to the subject! Is there a reason for the difference in behavior when it is observed vs unobserved?
Quantum mechanics is a semantic nightmare and is difficult to teach even to physics students. So I'll give you my simple input on this issue:
+ Show Spoiler [Trust me, this is simple.] +
In quantum mechanics, one of the major ways of examining systems (things doing stuff) is by using the concept of the wave function. The wave function is a complete abstraction - it is a mathematical entity that can be manipulated to get real answers to problems. Knowing how to setup a wave function for a specific system is something I won't even attempt to describe.
So why is this considered physics and not just mathematics? Well, let's say you have a system (en electron or something), and you wanna measure it (for whatever reason, physicists don't care). How do you represent that mathematically? How do you know what answer you will get when you measure?
What you do is this:
1. Figure out what quantity you're measuring.
2. Use the mathematical 'operator' associated with that quantity on the system's wavefunction.
3. The result is hopefully some constant times the wavefunction - so k*W(x,y,z,t).
In this case, the answer to "what will I get when I measure this?" is 'k'.
-----
It turns out that it's not quite this simple. Most wave functions are made of up a combination of a whole bunch of different functions. So
W = W1 + W2 + W3
What the hell does that mean? Well go back to your step-by-step process.
1. What quantity are you measuring (e.g. velocity)?
2. Use the 'velocity operator' on W.
3. The result is not quite what you were hoping for, it's
k1*W1 + k2*W2 + k3*W3
so does that mean you measure all of them(!!!!)? No - what this actually means is that you will measure one of the values k1, k2, or k3. Not all of them. You can use some tricky math to work out the probability that you will measure the individual terms, but you can never predict which one it will be.
-------
So what does that have to do with a system being observed?
Well the interpretation is that W = W1 + W2 + W3 is a system with three possible states. If you make the measurement of the system, you will measure k1 or k2 or k3 but never anything else.
What happens when you measure a system? So take the electron from earlier. We'll measure it's velocity. Let's say we get k2, and that k2 represents the electron moving off to the right at speed k2. Let's measure it again a little bit later. What do we get?
We sure as hell better get k2. If you measure something definitely happening, it better be definitely happening. So what does that mean for the wavefunction W?
Does W still equal W1 + W2 + W3? No, W = W2 because we have measured the system and know the answer. But that means we changed the wavefunction W just by measuring it. This is what is meant when people talk about observers. If there is some interaction that happens between your electron and something else, your electron most likely ends up in a definite state instead of in a probabilistic state. Observers don't have to people with eyes. Or cats. Or alive. Just something that interacts physically with the system.
/edit - Massive government-issue disclaimers for those who know about all the 'but what if...' cases I didn't talk about.
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On March 14 2010 05:46 Slow Motion wrote:
I think we should launch a preemptive nuke. It should reach by the time intelligent multicellular life develops.
the descolada!
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On March 14 2010 03:47 konadora wrote:
But does having all the necessary elements -> life? I'm pretty shitty at chemistry but my thinking is that having the 'materials' there doesn't necessary mean the end products will exist.
Yeah man, enough concentration and a little time can produce complex organic compunds. As the shit cools down, longer and more complex shit can be made.
It's like looking at our solar system a few billion years ago when all the shit was still forming.
Take formaldehyde and Hydrogen Cyanide. At high temperatures and if enough of the stuff is there the Cyanide can add to the C=O bond and make a simple amino acid.
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On March 15 2010 02:07 cUrsOr wrote:
I read the odds against all the exact chemicals and molecules that make up a cell, being in a pile, and randomly making a cell... being like almost impossible.
Self replicating protein chains and things like that would be really interesting, I wonder if they will every find anything like that in space. My guess would be no.
mRNA can self replicate.
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On March 17 2010 12:25 Rev0lution wrote:Show nested quote +On March 15 2010 02:07 cUrsOr wrote:
I read the odds against all the exact chemicals and molecules that make up a cell, being in a pile, and randomly making a cell... being like almost impossible.
Self replicating protein chains and things like that would be really interesting, I wonder if they will every find anything like that in space. My guess would be no. mRNA can self replicate.
assuming that the first life contained rna only
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HnR)hT
United States3468 Posts
On March 17 2010 09:49 DefMatrixUltra wrote:Show nested quote +On March 17 2010 04:28 decafchicken wrote:On March 15 2010 01:53 SpiritoftheTunA wrote:On March 15 2010 01:49 Housemd wrote:
This is interesting due to the fact that i having a conversation about it in class today with my math teacher.
HE says that the reason we can't travel the speed of light is due to the fact that this happens:
When we shoot a particle of light into a spectrum (or something, not quite sure) on the other end, the particle turns out to be TWO particles, each in a different location on some black paper they put as a "receiver". If we can find out what causes this, we can travel the speed of light to different galaxies. I think you're talking about this. http://en.wikipedia.org/wiki/Double-slit_experimentThis is an experiment that demonstrates the wave-particle duality of light. If you shoot a photon of light through two slits, and don't detect which slit it goes through, then the photon will act as if it went through both slits (even though it technically should be only one particle) and interfered with itself (as if it were a wave). This has to do with quantum mechanics, which I highly suggest you should learn in your academic future! To be honest, it doesn't have that much to do with the speed of light itself, but it's one of the things that got me interested in physics, so by all means, be open to the subject! Is there a reason for the difference in behavior when it is observed vs unobserved? Quantum mechanics is a semantic nightmare and is difficult to teach even to physics students. So I'll give you my simple input on this issue: + Show Spoiler [Trust me, this is simple.] +
In quantum mechanics, one of the major ways of examining systems (things doing stuff) is by using the concept of the wave function. The wave function is a complete abstraction - it is a mathematical entity that can be manipulated to get real answers to problems. Knowing how to setup a wave function for a specific system is something I won't even attempt to describe.
So why is this considered physics and not just mathematics? Well, let's say you have a system (en electron or something), and you wanna measure it (for whatever reason, physicists don't care). How do you represent that mathematically? How do you know what answer you will get when you measure?
What you do is this:
1. Figure out what quantity you're measuring.
2. Use the mathematical 'operator' associated with that quantity on the system's wavefunction.
3. The result is hopefully some constant times the wavefunction - so k*W(x,y,z,t).
In this case, the answer to "what will I get when I measure this?" is 'k'.
-----
It turns out that it's not quite this simple. Most wave functions are made of up a combination of a whole bunch of different functions. So
W = W1 + W2 + W3
What the hell does that mean? Well go back to your step-by-step process.
1. What quantity are you measuring (e.g. velocity)?
2. Use the 'velocity operator' on W.
3. The result is not quite what you were hoping for, it's
k1*W1 + k2*W2 + k3*W3
so does that mean you measure all of them(!!!!)? No - what this actually means is that you will measure one of the values k1, k2, or k3. Not all of them. You can use some tricky math to work out the probability that you will measure the individual terms, but you can never predict which one it will be.
-------
So what does that have to do with a system being observed?
Well the interpretation is that W = W1 + W2 + W3 is a system with three possible states. If you make the measurement of the system, you will measure k1 or k2 or k3 but never anything else.
What happens when you measure a system? So take the electron from earlier. We'll measure it's velocity. Let's say we get k2, and that k2 represents the electron moving off to the right at speed k2. Let's measure it again a little bit later. What do we get?
We sure as hell better get k2. If you measure something definitely happening, it better be definitely happening. So what does that mean for the wavefunction W?
Does W still equal W1 + W2 + W3? No, W = W2 because we have measured the system and know the answer. But that means we changed the wavefunction W just by measuring it. This is what is meant when people talk about observers. If there is some interaction that happens between your electron and something else, your electron most likely ends up in a definite state instead of in a probabilistic state. Observers don't have to people with eyes. Or cats. Or alive. Just something that interacts physically with the system.
/edit - Massive government-issue disclaimers for those who know about all the 'but what if...' cases I didn't talk about.
I would put it differently. It's not that quantum mechanics is difficult to teach to physics students; it's that it is not well understood by anyone at all. That's why all these perverse, practically-no-chance-of-being-right "interpretations" (many worlds, consciousness-causes-collapse, etc.) are floating around and being debated by philosophers who think about quantum mechanics for a living. Perhaps in this century someone will manage to explain the math rationally, to everyone's satisfaction...
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On March 18 2010 05:41 HnR)hT wrote:Show nested quote +On March 17 2010 09:49 DefMatrixUltra wrote:On March 17 2010 04:28 decafchicken wrote:On March 15 2010 01:53 SpiritoftheTunA wrote:On March 15 2010 01:49 Housemd wrote:
This is interesting due to the fact that i having a conversation about it in class today with my math teacher.
HE says that the reason we can't travel the speed of light is due to the fact that this happens:
When we shoot a particle of light into a spectrum (or something, not quite sure) on the other end, the particle turns out to be TWO particles, each in a different location on some black paper they put as a "receiver". If we can find out what causes this, we can travel the speed of light to different galaxies. I think you're talking about this. http://en.wikipedia.org/wiki/Double-slit_experimentThis is an experiment that demonstrates the wave-particle duality of light. If you shoot a photon of light through two slits, and don't detect which slit it goes through, then the photon will act as if it went through both slits (even though it technically should be only one particle) and interfered with itself (as if it were a wave). This has to do with quantum mechanics, which I highly suggest you should learn in your academic future! To be honest, it doesn't have that much to do with the speed of light itself, but it's one of the things that got me interested in physics, so by all means, be open to the subject! Is there a reason for the difference in behavior when it is observed vs unobserved? Quantum mechanics is a semantic nightmare and is difficult to teach even to physics students. So I'll give you my simple input on this issue: + Show Spoiler [Trust me, this is simple.] +
In quantum mechanics, one of the major ways of examining systems (things doing stuff) is by using the concept of the wave function. The wave function is a complete abstraction - it is a mathematical entity that can be manipulated to get real answers to problems. Knowing how to setup a wave function for a specific system is something I won't even attempt to describe.
So why is this considered physics and not just mathematics? Well, let's say you have a system (en electron or something), and you wanna measure it (for whatever reason, physicists don't care). How do you represent that mathematically? How do you know what answer you will get when you measure?
What you do is this:
1. Figure out what quantity you're measuring.
2. Use the mathematical 'operator' associated with that quantity on the system's wavefunction.
3. The result is hopefully some constant times the wavefunction - so k*W(x,y,z,t).
In this case, the answer to "what will I get when I measure this?" is 'k'.
-----
It turns out that it's not quite this simple. Most wave functions are made of up a combination of a whole bunch of different functions. So
W = W1 + W2 + W3
What the hell does that mean? Well go back to your step-by-step process.
1. What quantity are you measuring (e.g. velocity)?
2. Use the 'velocity operator' on W.
3. The result is not quite what you were hoping for, it's
k1*W1 + k2*W2 + k3*W3
so does that mean you measure all of them(!!!!)? No - what this actually means is that you will measure one of the values k1, k2, or k3. Not all of them. You can use some tricky math to work out the probability that you will measure the individual terms, but you can never predict which one it will be.
-------
So what does that have to do with a system being observed?
Well the interpretation is that W = W1 + W2 + W3 is a system with three possible states. If you make the measurement of the system, you will measure k1 or k2 or k3 but never anything else.
What happens when you measure a system? So take the electron from earlier. We'll measure it's velocity. Let's say we get k2, and that k2 represents the electron moving off to the right at speed k2. Let's measure it again a little bit later. What do we get?
We sure as hell better get k2. If you measure something definitely happening, it better be definitely happening. So what does that mean for the wavefunction W?
Does W still equal W1 + W2 + W3? No, W = W2 because we have measured the system and know the answer. But that means we changed the wavefunction W just by measuring it. This is what is meant when people talk about observers. If there is some interaction that happens between your electron and something else, your electron most likely ends up in a definite state instead of in a probabilistic state. Observers don't have to people with eyes. Or cats. Or alive. Just something that interacts physically with the system.
/edit - Massive government-issue disclaimers for those who know about all the 'but what if...' cases I didn't talk about. I would put it differently. It's not that quantum mechanics is difficult to teach to physics students; it's that it is not well understood by anyone at all. That's why all these perverse, practically-no-chance-of-being-right "interpretations" (many worlds, consciousness-causes-collapse, etc.) are floating around and being debated by philosophers who think about quantum mechanics for a living. Perhaps in this century someone will manage to explain the math rationally, to everyone's satisfaction...
Yes, part of the reason is that it openly tells you that things work in ways which humans aren't used to. The issue with quantum mechanics is that it's the realm of physics where instead of using your 'real' intuition, you have to use your 'mathematical' intuition in order to gain insight into problems.
From a semantical point of view, trying to describe something happening quantum mechanically is nightmarish. When talking about quantum mechanics to the general public (or even, like you say, in a philosophical sense), it's pretty much guaranteed that
a) You will not get your point across.
b) You will dig a semantic grave for yourself.
c) You will leave those interested mystified.
That's why I tried to bring some of the math in. It's the mathematical concepts which are key to 'understanding' quantum mechanics. Understanding it in a semantical sense just seems almost impossible.
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EPT
