Large Hardon Collider

[Seraph]

With all the problems and delays the LHC has suffered, I have doubts about the safety of it.

That's because it has fail-safes and safety features built in so that if there is a failure it immediately stops. The fact they are going to such great lengths to ensure it is functioning optimally should make you feel very safe.

Good food takes time. Good particle smashers take longer.

[Effluo]

The breakdown of the LHC was preordained. It was some cosmic karmic force that made it break.. It will again be delayed in startup and testing, and will not be fully functioning until Dec 21, 2012, at which time the world will come to an end, thanks to the LHC.

[Dimmauk]

A proton is made of 2 up quarks and 1 down quark, surrounded by gluons.

I think I've seen that porn before.

I had to wash my eyes out afterward.

[Woozie]

Thank you Neo that diagram on the other page makes so much more sense to me now.

Edit: so how do the fractional spins work? Do they just have to add up to one whole spin? Similar to the charge? Like if the proton is made of 2 up quarks and one down quark each one has to have a 1/3 spin?

There are no 1/3 spins. Spins are always integers or half integers. For quarks, all of their spins are 1/2. Mathematically, I don't think it's possible even in theory for a spin to be 1/3. Quantum states have to be symmetric or anti-symmetric, and 1/3 spin is neither. I can't see how a 1/3 would work out mathematically.

Charge, on the other hand, can be 1/3e. Quarks combine in a way so that their charge is always an integer. So if we wan to observe a 1/3e spin, we would have to look at an individual quark.

The interesting thing is that it is not possible to isolate a quark so that we can observe a 1/3 or 2/3 spin.

With gravity or electromagnetism, the force gets weaker as you pull two interacting particles apart. But with strong nuclear force (the force that binds quarks), the force gets stronger with distance until at a certain distance the force falls to zero. But by the time you get to that distance, the force was so huge that enough energy has been added to the system to create two new quarks. So if you take two quarks that are bound together and pull them apart, you end up with four quarks (two pairs of bonded quarks) instead of the original one pair of bonded quarks.

Another thing I am curious about is planck time (i believe i am using the correct term). Planck time is the shortest divisible segment of time that we can observe. What are some ideas as to the mechanics of the jumps between these times? As far as we can see, time is smoothe like an ass, but on a smaller scale its like those damn noise strips on the highway that jolt you out of that sound sleep at 80 mph. What goes on at sections of time shorter than planck?

Your questioned has been answered, but I wanted to add to it.

An interesting thing about plank time is its application to cosmology. Our laws of physics do not work for a certain period of time ATB (after the bang). This period of time is equal to plank time, which I believe is like a mere 10^-43 seconds (this period of time in the history of our universe is known as "Plank Epoch"). At this small time, our laws of physics have completely broken down, and the entire goal of cosmologist today is to figure out what happened in that tiny little time period ATB.The absolute biggest mystery in the history of science comes in such an incredibly small package. It's sort of frustrating. It would be like if a historian figured out the entire history of China except the first two minutes. And then the historian found out that even though he knows every single thing over thousands of years except for the very first two minutes, those first two minutes turned out to be so incredibly significant that his work is far from complete until he figures out that small time period. In fact, those mere two minutes could very well be much more important than the rest of the history combined.

Except this example is way more extreme, because instead of thousands of years depending on two minutes, it's 14billion years depending in one ten-millionth of a trillionth of a trillionth of a trillionth of a second.

So Planck time as a unit is similar to Kelvin in theory? And there is an Absolute Zero so to speak for time?

Uh, I guess you could say that. Absolute zero is the lowest temperature possible in theory, and plank time is the smallest time possible. But the similarities end there. I don't think Absolute zero and Plank Time are a good analogy. I can't think of a non-mathematical reason to explain why.

[zoobernut]

There are no 1/3 spins. Spins are always integers or half integers. For quarks, all of their spins are 1/2. Mathematically, I don't think it's possible even in theory for a spin to be 1/3. Quantum states have to be symmetric or anti-symmetric, and 1/3 spin is neither. I can't see how a 1/3 would work out mathematically.

Charge, on the other hand, can be 1/3e. Quarks combine in a way so that their charge is always an integer. So if we wan to observe a 1/3e spin, we would have to look at an individual quark.

The interesting thing is that it is not possible to isolate a quark so that we can observe a 1/3 or 2/3 spin.

With gravity or electromagnetism, the force gets weaker as you pull two interacting particles apart. But with strong nuclear force (the force that binds quarks), the force gets stronger with distance until at a certain distance the force falls to zero. But by the time you get to that distance, the force was so huge that enough energy has been added to the system to create two new quarks. So if you take two quarks that are bound together and pull them apart, you end up with four quarks (two pairs of bonded quarks) instead of the original one pair of bonded quarks.

I am really interested in the particle physics stuff. Do you have any beginner books that are more up to date or resources that are more up to date that I can start with to get my feet wet so to speak?

Also I am not sure I follow you about the 1/2 spin vs. the 1/3 spin thing I understand the concept that all the sub-particles that make up a proton must add up to an integer spin but if you have two up quarks and 1 down quark then wouldn't their spin be 1/3? How do you maintain that symmetry that you are talking about in Quantum states if there are three particles?

[aurik]

I am really interested in the particle physics stuff. Do you have any beginner books that are more up to date or resources that are more up to date that I can start with to get my feet wet so to speak?

Also I am not sure I follow you about the 1/2 spin vs. the 1/3 spin thing I understand the concept that all the sub-particles that make up a proton must add up to an integer spin but if you have two up quarks and 1 down quark then wouldn't their spin be 1/3? How do you maintain that symmetry that you are talking about in Quantum states if there are three particles?

Protons have a spin of +1/2. You may be confusing spin and charge.

[zoobernut]

Protons have a spin of +1/2. You may be confusing spin and charge.

Yeah I see I was mixing up spin and charge. But if you have a proton and it is made up by 2 up quarks and 1 down quark that is an odd number of particles and the three spins combined (1/2) do not equal a whole number. That is what I was confused about.

[zoobernut]

That is BS Miz, Effluo was coming into this thread without adding anything constructive.

Woozie when you pull two quarks apart and you get to that point where the force between them jumps to 0 where do the two extra quarks come from? Are they created out of the energy released as the bond is broken? Maybe I need to understand the relationship of up quarks and down quarks better but if this is true how can you have an odd number of quarks in a particle? (going back to the idea that a proton is 2 up quarks and 1 down quark.)

[zoobernut]

Why does everything I love get destroyed?

[Kryssan]

Oh man, the LHC scares me.

I think we've all seen at least one sci-fi movie when something similar to this goes wrong, and we either have demons, an alien race bent on dominating the human species, or black holes fuck us up. With all the problems and delays the LHC has suffered, I have doubts about the safety of it.

Ah yes, the superfluous I saw it in the movies or I read it in a book. Projects as large as the LHC will suffer setbacks. NIF is a great example of this. NIF has suffered setbacks dealing with everything from people afraid of nuclear power to large ancient archeological dig findings. Things happen. Stuff breaks. However, because we are aware of the fact that O'Leery's Law (Murphy was an optimist, for those who haven't heard it) exists, there are insanely intense safety procedures and protocols that go into these things. And most of the time, even in the worst case design basis failure event, these safety actions are ridiculously overexamined. Commercial power plants are some of the best examples of this. Quite a few commercial power plants have touring facilities, did you know that? Yes, you can request a tour. You can go see for yourself the levels of safety and protection a plant has. So the next time someone mentions on the news how they're "increasing security" at the nuclear power plant, you can laugh your ass off and go "What, they bought them tanks?" They're probably not going to get too indepth with you regarding reactor/engineered safeguards or safety, and how it is assured, and under what conditions, but you can at least learn a few things about it.



However, what needs to be pointed out here, and what you are most assuredly not helping with, is the craptastic media spreadage of rumours and junk. People fear what they do not understand. Ok. Just... ok. I can buy this. So go LEARN ABOUT IT. Stop jumping on the bandwagon. You strike me as the person that would be one of the gung-ho happy Greenpeace treehuggers that gladly spraypaints the side of a carrier protesting nuclear power. Yeah. 'Cause, like all that spraypaint flowing off into the water is doing soooo much good for the environment, isn't it? Everywhere I go I run into people who think radioactive waste comes in a 55 gallon drum and is generally some thick vicious green glowing liquid. It makes me laugh how truly sad and degenerate this line of thinking is. Especially when you could just go learn about it and realize how stupid some of these assertions are.

[Sera]

Things I learned in college:
Anatomy is really biology
Biology is really chemistry
Chemistry is really physics
Physics is really math
Math is really hard

http://imgs.xkcd.com/comics/purity.png
???

[Purrrfect]

Excellent thread guys.^^ Usually I peruse my BG in the morning and move on in an hour or so to other sites, but today I was reading this thread all day long when I got time. That written inner monologue of max's a couple pages back was great lol. Looking forward to more stuff from you guys tomorrow.^^ (ashamed to say I remember absolutely nothing from my diffEQ class a couple years ago, but then again I have never used it... I imagine my recent vector calculus class will go the same way.)

[Woozie]

Yeah I see I was mixing up spin and charge. But if you have a proton and it is made up by 2 up quarks and 1 down quark that is an odd number of particles and the three spins combined (1/2) do not equal a whole number. That is what I was confused about.

I may have mispoken earlier. Charge is always a whole number (times e), but charge can be half or whole.

The thing you have to remember about spin is that it can point in two different directions. So you can have two particles with a spin of 1/2, put them together, and get a spin of either 1. But you can also get a total of 1/2 if the two spins are in different directions.

For example, a proton is made of up up down.

Up has a charge of +2/3, and down has a charge of -1/3. So (+2/3) + (+2/3) + (-1/3) = (+3/3) = +1. This is why a proton's charge is +1.

As for spin, a proton's spin, we have (+1/2) + (-1/2) + (+1/2) = (+1/2). One of the quarks always points the opposite direction so the spin always comes out to an absolute value of 1/2. Sometimes you'll measure +1/2 and sometimes you'll measure -1/2, but you'll always measure an absolute value of 1/2 because one quark is always pointing the other way.

That is BS Miz, Effluo was coming into this thread without adding anything constructive.

Woozie when you pull two quarks apart and you get to that point where the force between them jumps to 0 where do the two extra quarks come from? Are they created out of the energy released as the bond is broken? Maybe I need to understand the relationship of up quarks and down quarks better but if this is true how can you have an odd number of quarks in a particle? (going back to the idea that a proton is 2 up quarks and 1 down quark.)

Your understanding is correct; the energy released from breaking a bond between two quarks is strong enough to create two more quarks. The example I gave applies to mesons (which is a quark bonded to an antiquark. Pulling apart the quark and antiquark creates a quark antiquark pair which bonds to the original two quarks. The end result is two mesons instead of one).

A proton is a baryon, meaning it's made of three quarks instead of a quark and antiquark. I'm not 100% sure on the mechanics of pulling a quark off of a proton. When particles are created out of nothingness (well, when they're created because of extra energy laying around in space), they occur in matter/antimatter pairs. So in the case of a baryon that doesn't originally have a baryon, I, I'd assume whatever you pull off would bond with the anti-particle that is created, and the regular particle would become part of the proton.

[zoobernut]

I may have mispoken earlier. Charge is always a whole number (times e), but charge can be half or whole.

The thing you have to remember about spin is that it can point in two different directions. So you can have two particles with a spin of 1/2, put them together, and get a spin of either 1. But you can also get a total of 1/2 if the two spins are in different directions.

For example, a proton is made of up up down.

Up has a charge of +2/3, and down has a charge of -1/3. So (+2/3) + (+2/3) + (-1/3) = (+3/3) = +1. This is why a proton's charge is +1.

As for spin, a proton's spin, we have (+1/2) + (-1/2) + (+1/2) = (+1/2). One of the quarks always points the opposite direction so the spin always comes out to an absolute value of 1/2. Sometimes you'll measure +1/2 and sometimes you'll measure -1/2, but you'll always measure an absolute value of 1/2 because one quark is always pointing the other way.



Your understanding is correct; the energy released from breaking a bond between two quarks is strong enough to create two more quarks. The example I gave applies to mesons (which is a quark bonded to an antiquark. Pulling apart the quark and antiquark creates a quark antiquark pair which bonds to the original two quarks. The end result is two mesons instead of one).

A proton is a baryon, meaning it's made of three quarks instead of a quark and antiquark. I'm not 100% sure on the mechanics of pulling a quark off of a proton. When particles are created out of nothingness (well, when they're created because of extra energy laying around in space), they occur in matter/antimatter pairs. So in the case of a baryon that doesn't originally have a baryon, I, I'd assume whatever you pull off would bond with the anti-particle that is created, and the regular particle would become part of the proton.

Wow that is really fascinating. Is the creation of the new Quarks out of that energy similar to the big bang? It seems as though whatever is happening at that moment is fundamental to the structure of our universe and how matter was created early on.

Check the bold word above. That is supposed to be spin right? If that is supposed to be spin then it makes sense to me now. So I can get a mental grasp of what we are talking about I understand what charge refers to but what on a physical level is the spin referring to? Is it spinning on axis or am I taking the term spin too literal? If it is literally spin then what happens when it reaches the end of its half spin does it spin back the opposite direction? I can't quite understand how a half spin would work.

[Neosutra]

Not really similar to the big bang in any way, but it does show some insight into particles and anti-particles.

And yes his bold word should be spin, and was based on the summed spin of a particle.

[Woozie]

I am really interested in the particle physics stuff. Do you have any beginner books that are more up to date or resources that are more up to date that I can start with to get my feet wet so to speak?

A really good book specifically about particle physics is The Particle Garden (by Gordon Kane) or the God Particle. Both are over 10 or 15 years old, but that's not a big deal.

Despite all the hype surrounding particle physics, it's actually one of the slowest advancing form of physics today. If someone stopped studying solid-state physics 10 years ago, they'd be waaaaaaaaaay out of the loop (well, depending on which are of solid state physics they were in). But someone who stopped studying particle physics 10 years ago is only slightly out of the loop, and would be back up to date very quickly. We only learn like one or two new things every year or two and most of it is "Hubble Space Telescope finds Biggest Supernova" (which isn't even particle physics but you get the point).

Something HUGE happens much less often. Most of the other news we get is some theorists opinion on something string theory or something, which often disagrees with every other theorist out there but gets attention anyways just because it's interesting.

So all you really need to do is read some of the books mizango listed earlier, and don't worry about the fact that most were written over a decade ago. My personal favorites are:

The End of Physics (by David Lindley)
The Elegant Universe (by Brian Greene)
The Fabric Of the Cosmos (by Brain Greene)
The God Particle (Leon Linderman (sp?))
The Feynman Lectures (very old, out of date, and isn't written with a general audience in mind like the other books, but is very good if you're willing to read them).

The Elegant Universe and The God Particle have had documentaries, which you can probably find online or bug mizango about. I still haven't seen the God Particle documentary yet, but I've read the book.

The End of Physics is about GUTs and TOEs, but about 75% of the book is dedicated to explaining the physics behind it (quantum physics, particle physics, GR, cosmology, etc)

The Elegant Universe is about String Theory, but again, about 75% of the book is about the physics behind it (which is the same as in the previous book since String Theory is a GUT and possibly a TOE [it's very likely that any TOE is a GUT and vice versa, but it's possible that we may find a GUT and it wont be a TOE. A GUT could technically unify the forces but still leave open questions])

The Fabric Of the Cosmos has a really great section explaining entropy, and a section about the delayed choice quantum eraser.

The God particle is also dedicated solely to particle physics (specifically the higgs boson, but only like 1% of the book even talks about the higgs boson. He didn't even mention the higgs boson until like page 300. The rest is about his experiences in particle physics. This book is largely historical, explaining the history of particle physics, while at the same time educating you on the current state of particle physics).

Like I said, don't worry too much about a book being up to date. If it's less than 20 years old it's probably up to date on 95% of theoretical physics.

Subscribe to Scientific American or visit the website often. That way if anything huge comes up, you'll learn about it there.

Edit: Let me clarify something. When I refer to new advanced in theoretical physics, I mean some sort of experimental or observational confirmation. We come up with new theories and new solutions to old theories all the time, but it's rare to find some new huge observation like dark energy. Things like that happen rarely, but hopefully the LHC changes that.

[zoobernut]

Kinda going along the same thought path, if you have two quarks and you pull them apart and then you have 4 quarks doesn't that stand to say that the other two quarks always existed just in a state that we could not see them? Or is it that the energy they come from existed and it just took that event to convert the energy into the quarks? If you have a particle and an anti particle and they collide do they annihilate each other in a burst of energy or do they do something else and can be pulled back apart somehow?

[Woozie]

Wow that is really fascinating. Is the creation of the new Quarks out of that energy similar to the big bang? It seems as though whatever is happening at that moment is fundamental to the structure of our universe and how matter was created early on.

Check the bold word above. That is supposed to be spin right? If that is supposed to be spin then it makes sense to me now. So I can get a mental grasp of what we are talking about I understand what charge refers to but what on a physical level is the spin referring to? Is it spinning on axis or am I taking the term spin too literal? If it is literally spin then what happens when it reaches the end of its half spin does it spin back the opposite direction? I can't quite understand how a half spin would work.

What Neo said. I meant to say spin.

You are taking spin too literally. Quarks can be thought of as either points in space or waves (or strings?). It makes no sense to talk about a point spinning or a wave spinning. Balls can spin because they're extended in space and they spin about some axis. Particles aren't tiny balls, and they don't literally spin.

Let's look at our solar system for a moment. The earth has angular momentum. Angular momentum has two varieties. Once comes from the entire objects motion around some point (e.g. the Earth has angular momentum due to it's revolving around the sun) and the other variety comes from spinning about an axis (e.g. the earth has angular momentum due to spinning on it's axis). The total angular momentum is the sum of the two forms. The second form of angular momentum (the spin) is intrinsic. It depends only on the earth and it's motion and it's properties. If the sun were to disappear and the earth went flying into space, it wouldn't affect the spin component of its angular momentum at all.

Although elementary particles can't spin due to the reasons explained above, they do still have intrinsic angular momentum. When this was first discovered, the first line of thought was "these electrons must be spinning on an axis! How else could they have intrinsic angular momentum?". Some of the math actually worked out too when this was assumed, but the models weren't entirely consistent. Eventually we had to throw out the idea of a particle spinning on an axis, but we didn't throw out the name "spin".

The best way to understand spin is to not try to understand spin, lol. Heck, the same can be said of anything in QM. Spin works well mathematically, but it's nearly impossible to try to compare it or understand it.

Another mathematical note:
In quantum mechanics, any observable (i.e. anything that can be measured) corresponding to something from classical physics must have an operator built based on the classical representation. This is an example of what I mean by that:

In classical physics, kinetic energy is p^2/2m, where p is momentum and m is mass. So in quantum physics, we have

kinetic energy = P^2/2m, where p is in bold because it's the momentum quantum operator (meaning if you do P times F, where F is some quantum wave function, then F is changed into a new wave function depending on the rules set forth by P).

So any quantum representation of a physical phenomenon is the same as it's classical representation, but with operators.

The operators for quantum mechanical spin does not correspond to anything from classical physics, so there's no use trying to compare spin with any everyday phenomenon.

[Woozie]

Kinda going along the same thought path, if you have two quarks and you pull them apart and then you have 4 quarks doesn't that stand to say that the other two quarks always existed just in a state that we could not see them? Or is it that the energy they come from existed and it just took that event to convert the energy into the quarks? If you have a particle and an anti particle and they collide do they annihilate each other in a burst of energy or do they do something else and can be pulled back apart somehow?

Or is it that the energy they come from existed and it just took that event to convert the energy into the quarks?

This is the correct answer.

If a particle collides with it's antiparticle, it will always annihilate. They can be pulled part before they annihilate, as Stephen Hawkings theorized in his black hole evaporation model.

For quarks, I don't think a quark is being paired with its own antiquark. That's why they can be pulled apart. I'm not too sure about this though because I have seen equations involving up bonded with anti up. I'm not sure how that would work out.

[zoobernut]

Thanks for clearing that up it was very confusing to see the term spin and think of it in a classical physics way. So spin refers to the particle's intrinsic angular momentum.