The Official Cricketweb Science Thread! - Page 2

luckyeddie · 07-08-2002, 09:02 AM

Another answer for Roy. Please note that Quantum Mechanics is not one of my strong suits. If anyone can add to the explanation, please feel free to do so.

... explain the uncertainty principle

Heisenberg's Uncertainty Principle states that "The more precisely the POSITION is determined, the less precisely the MOMENTUM is known in this instant, and vice versa".

What he is referring to here is subatomic particles, in particular electrons.

My first thought is that he could have actually reduced that principle still further, since momentum is mass times velocity. The mass of an electron is known and does not vary, therefore the momentum is directly proportional to its velocity. Consequently, Heisenberg's principle OUGHT to read "The more precisely the POSITION is determined, the less precisely the VELOCITY is known in this instant, and vice versa".

That's not an answer, is it? OK, I'll try again.

In order to determine anything (position, velocity, momentum) to do with a particle, I have to MEASURE it. Now, each measurement has some error built into it (you can never measure anything precisely). Fine so far? OK. Now, let's assume that our accuracy of measuring things is improving. Eventually, we become so good at measuring that we can say, to all intents and purposes, we are 'spot on'.
Now, we take our super-duper ultra-accurate Vernier calipers or atomic clock or whatever, and we introduce it to the system where we have our electron which is whizzing around. We get closer to the flipping electron until, eventually, we bump into it (disturb it really, and move it, so it's no longer where we thought it was). Not only that, we have also disturbed our measuring device too, but that's another story.
Maybe Heisenberg can help me find my car keys.

Only two brain cells left, now. Heisenberg v Erwin Schrodinger will have to wait.

Can't we have questions about biomechanics, so one of our other eggheads can have a go? Why is it always the physics and the momentum and the black holes and the quantum mechanics (Burhey!)?

I'm not touching self-replicating DNA with yours.

Gotchya · 07-08-2002, 09:59 AM

Okee here goes nothing......

When a physicist refers to a singularity he or she is generally referring to a quantity which is infinite. Specifically, a quantity which approaches infinity as another parameter goes to zero, such as

lim 1/X = there's nothing on my keyboard
X ->0 forinfinity!

It isn't true to say that all laws of physics break down at a singularity. You can imagine the problems though -- how do we interpret an infinite mass or infinite energy or infinite force? Usually we assume that there is some new set of laws or some new way of looking at the problem that makes the apparent singularity go away.(That is we have to change our perception of the problem)

Here's an example. You may be familiar with Hooke's law for the force exerted by a spring: F=kx where k is the tension of the spring and x is the distance it is stretched. Now write the equation as k=F/x. Written this way it would seem that if you compare the tension between any two points on the spring, it grows and grows the closer together the two points are. In fact, two points spaced infinitesimally apart seem to have an infinite tension! It's just a manifestation of the 1/x limit above.

But of course that's not true. If you really want to know what's happening at small distance scales you can't use the Classical physics behind Hooke's law. At some point x drops below the spacing between molecules in the spring's metal. Now Hooke's law no longer applies and you have to use atomic physics to explain the spring's properties. So in the large-scale theory (Hooke's law) there was no fundamental distance scale: x could be as small as you want. But at some point this law breaks down. In the small-scale theory (quantum mechanics and atomic physics) there is a fundamental distance scale: the atomic spacing. We would say that the singularity has been "resolved."

Most people worry about singularities involving general relativity: two examples being a black hole and the singularity that classical general relativity predicts was our universe at the moment it began. If you try to apply the laws of general relativity in these situations you will inevitably find the same 1/x singularities I've been talking about. How are we going to resolve these singularities? We expect quantum mechanics to do the job, since it is the theory that correctly describes physics at small distance scales. Unfortunately, while we have good theories of atomic physics, we don't real have a good theory of quantum gravity. Many of us think string theory will ultimately provide the resolution to these problems.

In short then, a singularity represents an infinity and we generally don't think nature is infinite. The problem arises from not having some kind of "floor" built into a theory that keeps you from taking the limit of 1/x as x goes to zero. The way out is to apply a new theory that has such a floor, such as quantum mechanics or string theory (quantum gravity).
Hope that answered some of ur questionz, as far as the matters of God and the big bang go, i could refer you to read Stephen Hawkings A brief history of time (although personally, i think he is out to prove that God does not exist, or even if he did he didn't have much choice in creating the heavens the way they are !!!)
apologies for any mistakes i may have made.

luckyeddie · 07-08-2002, 10:33 AM

I'm impressed.

And pointing people in the direction of "Lisa's robot buddy" (Stephen Hawking) is definitely the way to them interested in physics.

I think that your definition of a singularity could have been slightly better illustrated by using 'infinite mass, zero diameter' as an example, but what the heck.

Now, how's about tackling 'Fermat'? Then I can retire gracefully to third man.

luckyeddie · 07-08-2002, 11:47 AM

It is fitting that 'string theory' should be mentioned at this moment in time.

Paul Dirac, arguably the 'father' of string theory, was born on August 8, 1902.

anthonysw · 07-08-2002, 04:47 PM

What a great thread.

Very interesting stuff!!

Top_Cat · 07-08-2002, 05:07 PM

What, no-one's got any chemistry questions? Pfft! I'm insulted..........

Quote:

Why is the sky blue?
Easypeasy. It's all down to the scattering of light. Photons normally travel in straight lines, but when one hits a nitrogen molecule or another particle in the Earth's atmosphere, it undergoes a 'scattering' process, i.e. some of it's energy bounces off in a different direction. The actual direction is determined by the actual wavelength of the light, the size of the particle it hits and so on. For the makeup of our atmosphere, this effect is greatest in the shorter (blue end of the spectrum) wavelengths, and that's why the sky appears to be blue.

The phenomenon eddie's talking about here is Rayleigh Scattering, if you want to look for a mathematical description of it on the net (which tells you more if you can understand the maths).

Quote:

how do scientists know that protein synthesis happens by the unzipping of dna, followed by the mRNA transcribing the information and the tRNA translating it and it being turned into amino acids in ribosomes in our cells.

The short answer is that no-one know 'why' it happens. We've just been able to observe it. To 'watch' any biological phenomena, you just have to radioactively label a certain peptide (like one of the RNA's for example) and watch where it goes and what happens to it. I personally watched as proteins get synthesised at the ribosomes and it's a pretty dull and slow process.

Gotchya: Pick the engineer.

anthonysw · 07-08-2002, 11:40 PM

hmm a chemistry question...

How does an atom bomb work?

Top_Cat · 07-08-2002, 11:46 PM

Quote:

hmm a chemistry question...

How does an atom bomb work?

1) It's more of a physics question because the chemistry ain't that complex.

2) Are you wanting to know about how the original fission atom bomb worked, how a fusion or hydrogen bomb work or how a neutron bomb works. It's quite a lot of info.

Anyway, here's a great explanation.

http://www.howstuffworks.com/nuclear-bomb.htm

Maybe a better aproach would be to read that and ask some questions about it that might not be answered.

Anyone wanna know how a chemical weapon like a nerve gas (e.g. VX Gas) works??

p.s. Tony, if you want to see a great vid I've got on the history of the atomic and nuclear weapons programs like Trinity and the tests at Bikini Atol, just ask.

[Edited on 8/7/02 by Top_Cat]

yaju · 07-08-2002, 11:56 PM

Why do people fall in love(Kyun Hota Hai Pyarrr)?

Why are females always ill-treated?

When will pastures turn green for women?

Is there really rebirth after death?

Will the lord come on earth again?

anthonysw · 07-08-2002, 11:59 PM

I sure would love to view the vid. Funny when I was at school I was against any sort of learning. These days I could watch National Geographic, History Channel and Discovery all day

[Edited on 8/8/02 by anthonysw]

anthonysw · 07-08-2002, 11:59 PM

I sure would love to view the vid.

Funny that when I was at school I was against any sort of learning.

These days I could watch National Geographic, History Channel and Discovery all day

Top_Cat · 08-08-2002, 12:02 AM

Funny Yaju, I could have sworn this was a science thread.

royGilchrist · 08-08-2002, 12:39 AM

Quote:

I think that your definition of a singularity could have been slightly better illustrated by using 'infinite mass, zero diameter' as an example, but what the heck.

Is the mass infinite (like you said Eddie) in the case of a singularity, or is mass finite but very large (what I think), and because of zero diameter (zero volume), the density goes to infinity?

Thanks all three of u, TC, LE and Gotchya for the very useful info. If this thread goes somewhere maybe we could publish this on a website somewhere as a science FAQ.

Now, as for Stephen Hawking, I enver read his BHOT but read part of another book by him, and found it kinda interesting. Explained gravity as curvature as opposed to force really simply for us lay people, and also the way he proved newton wrong (the gravitational force between two bodies) was quite ingenious I thought.

Continuing on the singularity/black hole topic...black hole by definiton is concentrated mass, which has formed due to no more hydrogen left on a star to keep it from collapsing onto itself, and hence nothing that comes near it can escape due to the enormous gravity. Now is there a way to find out what happens inside a black hole, and is it possible that every black hole goes on collapsing and eventually becomes a black hole?

Also, as someone said that we still havent got the complete hang of quantum mechanics (physics of the very small). If we do, would we know the 'history' just before big bang? Did Einstein work on quantum mechanics as well? How successful was he if he did?

Just to refresh one question, scrodinger's cat experiment is still unexplained, whenever u get the chance LE u could explain it, no hurry.

Chemistry question, hmm... why is a fusion reaction, and the subsequent method of producing electricity supposed to be the safest. I kinda know that its because the by product of hyderogen is helium (totally stable) and water, but a detailed explanation would be better. Also, are there any harmful effects of fusion that we are not told about, to sell this idea of fusion as an energy source. And why is there so much opposition against it.

Are there any fusion reactors presently producing energy. Also, why do they say that if there is a fusion bomb, it would not harm the buildings but only people?

Please correct me if any of the info above is incorrect.

Gotchya · 08-08-2002, 12:49 AM

Hey guyz anyone here ever watch the x files

hey hey aint a spooky just pointing to the to how scientifically unscientific the show was, BUT that was what really got me interested in Science...

Tis an offtopic forum isn;t it?

yaju · 08-08-2002, 12:51 AM

Funny? Ill-treatment of women funny?

Anyway why do we visit CricketWeb?

What does g-orbital stand for? Any further information about it?

07-08-2002, 09:02 AM	#16 (permalink)
luckyeddie Hall of Fame Member Join Date: Jun 2002 Location: Derby, England Posts: 17,631	Another answer for Roy. Please note that Quantum Mechanics is not one of my strong suits. If anyone can add to the explanation, please feel free to do so. ... explain the uncertainty principle Heisenberg's Uncertainty Principle states that "The more precisely the POSITION is determined, the less precisely the MOMENTUM is known in this instant, and vice versa". What he is referring to here is subatomic particles, in particular electrons. My first thought is that he could have actually reduced that principle still further, since momentum is mass times velocity. The mass of an electron is known and does not vary, therefore the momentum is directly proportional to its velocity. Consequently, Heisenberg's principle OUGHT to read "The more precisely the POSITION is determined, the less precisely the VELOCITY is known in this instant, and vice versa". That's not an answer, is it? OK, I'll try again. In order to determine anything (position, velocity, momentum) to do with a particle, I have to MEASURE it. Now, each measurement has some error built into it (you can never measure anything precisely). Fine so far? OK. Now, let's assume that our accuracy of measuring things is improving. Eventually, we become so good at measuring that we can say, to all intents and purposes, we are 'spot on'. Now, we take our super-duper ultra-accurate Vernier calipers or atomic clock or whatever, and we introduce it to the system where we have our electron which is whizzing around. We get closer to the flipping electron until, eventually, we bump into it (disturb it really, and move it, so it's no longer where we thought it was). Not only that, we have also disturbed our measuring device too, but that's another story. Maybe Heisenberg can help me find my car keys. Only two brain cells left, now. Heisenberg v Erwin Schrodinger will have to wait. Can't we have questions about biomechanics, so one of our other eggheads can have a go? Why is it always the physics and the momentum and the black holes and the quantum mechanics (Burhey!)? I'm not touching self-replicating DNA with yours. __________________ Nigel Clough's Black and White Army, beating Forest away with 10 men

07-08-2002, 09:59 AM	#17 (permalink)
Gotchya State Vice-Captain Join Date: Aug 2002 Location: Lahore, Pakistan Posts: 1,399	Okee here goes nothing...... When a physicist refers to a singularity he or she is generally referring to a quantity which is infinite. Specifically, a quantity which approaches infinity as another parameter goes to zero, such as lim 1/X = there's nothing on my keyboard X ->0 forinfinity! It isn't true to say that all laws of physics break down at a singularity. You can imagine the problems though -- how do we interpret an infinite mass or infinite energy or infinite force? Usually we assume that there is some new set of laws or some new way of looking at the problem that makes the apparent singularity go away.(That is we have to change our perception of the problem) Here's an example. You may be familiar with Hooke's law for the force exerted by a spring: F=kx where k is the tension of the spring and x is the distance it is stretched. Now write the equation as k=F/x. Written this way it would seem that if you compare the tension between any two points on the spring, it grows and grows the closer together the two points are. In fact, two points spaced infinitesimally apart seem to have an infinite tension! It's just a manifestation of the 1/x limit above. But of course that's not true. If you really want to know what's happening at small distance scales you can't use the Classical physics behind Hooke's law. At some point x drops below the spacing between molecules in the spring's metal. Now Hooke's law no longer applies and you have to use atomic physics to explain the spring's properties. So in the large-scale theory (Hooke's law) there was no fundamental distance scale: x could be as small as you want. But at some point this law breaks down. In the small-scale theory (quantum mechanics and atomic physics) there is a fundamental distance scale: the atomic spacing. We would say that the singularity has been "resolved." Most people worry about singularities involving general relativity: two examples being a black hole and the singularity that classical general relativity predicts was our universe at the moment it began. If you try to apply the laws of general relativity in these situations you will inevitably find the same 1/x singularities I've been talking about. How are we going to resolve these singularities? We expect quantum mechanics to do the job, since it is the theory that correctly describes physics at small distance scales. Unfortunately, while we have good theories of atomic physics, we don't real have a good theory of quantum gravity. Many of us think string theory will ultimately provide the resolution to these problems. In short then, a singularity represents an infinity and we generally don't think nature is infinite. The problem arises from not having some kind of "floor" built into a theory that keeps you from taking the limit of 1/x as x goes to zero. The way out is to apply a new theory that has such a floor, such as quantum mechanics or string theory (quantum gravity). Hope that answered some of ur questionz, as far as the matters of God and the big bang go, i could refer you to read Stephen Hawkings A brief history of time (although personally, i think he is out to prove that God does not exist, or even if he did he didn't have much choice in creating the heavens the way they are !!!) apologies for any mistakes i may have made. __________________ Once the game is over, the king and the pawn go back in the same box

07-08-2002, 04:47 PM	#20 (permalink)
anthonysw U19 Cricketer Join Date: Apr 2002 Location: (Adelaide) Australia Posts: 403	What a great thread. Very interesting stuff!! __________________ -----------------My Signature-----------------

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07-08-2002, 10:33 AM	#18 (permalink)
luckyeddie Hall of Fame Member Join Date: Jun 2002 Location: Derby, England Posts: 17,631	I'm impressed. And pointing people in the direction of "Lisa's robot buddy" (Stephen Hawking) is definitely the way to them interested in physics. I think that your definition of a singularity could have been slightly better illustrated by using 'infinite mass, zero diameter' as an example, but what the heck. Now, how's about tackling 'Fermat'? Then I can retire gracefully to third man.

07-08-2002, 11:47 AM	#19 (permalink)
luckyeddie Hall of Fame Member Join Date: Jun 2002 Location: Derby, England Posts: 17,631	It is fitting that 'string theory' should be mentioned at this moment in time. Paul Dirac, arguably the 'father' of string theory, was born on August 8, 1902.

07-08-2002, 11:40 PM	#22 (permalink)
anthonysw U19 Cricketer Join Date: Apr 2002 Location: (Adelaide) Australia Posts: 403	hmm a chemistry question... How does an atom bomb work?

07-08-2002, 11:59 PM	#25 (permalink)
anthonysw U19 Cricketer Join Date: Apr 2002 Location: (Adelaide) Australia Posts: 403	I sure would love to view the vid. Funny when I was at school I was against any sort of learning. These days I could watch National Geographic, History Channel and Discovery all day [Edited on 8/8/02 by anthonysw]

07-08-2002, 11:59 PM	#26 (permalink)
anthonysw U19 Cricketer Join Date: Apr 2002 Location: (Adelaide) Australia Posts: 403	I sure would love to view the vid. Funny that when I was at school I was against any sort of learning. These days I could watch National Geographic, History Channel and Discovery all day

08-08-2002, 12:02 AM	#27 (permalink)
Top_Cat Cricket Web: All-Time Legend Join Date: Feb 2002 Location: Adelaide, South Australia Posts: 21,196	Funny Yaju, I could have sworn this was a science thread.

08-08-2002, 12:49 AM	#29 (permalink)
Gotchya State Vice-Captain Join Date: Aug 2002 Location: Lahore, Pakistan Posts: 1,399	Hey guyz anyone here ever watch the x files hey hey aint a spooky just pointing to the to how scientifically unscientific the show was, BUT that was what really got me interested in Science... Tis an offtopic forum isn;t it?

08-08-2002, 12:51 AM	#30 (permalink)
yaju State Vice-Captain Join Date: Nov 2001 Location: Jalandhar, Punjab, India Posts: 1,313	Funny? Ill-treatment of women funny? Anyway why do we visit CricketWeb? What does g-orbital stand for? Any further information about it?

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