Science discussion, continued from other thread

[michaeld]

Well the top quark to a W boson + a bottom quark actually. Note the North-East leg of the Feynman diagram. (Also, of course, the bottom quark is needed to conserve baryon number - and charge for that matter.)

Oh, yes, I know. I had the bottom quark in my original sentence, but when it all got assembled and posted, that part seems to have disappeared. :redface:

Yes, we see that in the diagram.

*goes back into hiding*

Well don't worry about it; I actually omitted the boson in my initial sketch, to save typing (as I wasn't trying to be totally precise anyway).

Here is another way of looking at that diagram, but also rotating it to see the creation of a top quark:

Cool diagram. Of course it was one of Feynman's most well known insights, that a time reversed particle is equivalent to its anti-particle (more precisely, the known laws of physics are CPT invariant); the rotation illustrates that nicely, as the b and q acquire bars in the q+q-bar -> t+b-bar reaction.

[michaeld]

Oh and Joe, you can't get more real than microscopic physics. In fact, microscopic physics is the key to understanding the macroscopic world at a deep level.

Yep, if you understand it at the microscopic level, you can in principle work your way up. As this is often easier said than done, a lot of our understanding of the macroscopic world first has to be empirical while waiting for the bottom up understanding to follow later.

Of course. Moreover all of our understanding of the microscopic world ultimately comes from the macroscopic world. (Even if you do a microscopic particle physics experiment, we need a macroscopic outcome - for example the position of a dial - for our brains to be able to process it.) And yet, from another point of view, the microscopic world is more fundamental than the macroscopic world.

It's an interesting general philosophical point, that the epistemic and ontological "hierarchies of fundamentalness" very often point in opposite directions, as this example illustrates.

[Herr Joseph von Löthing]

Not as fun as mechanics, though.

Joseph can solve the Three Body Problem.

I'd say it's just probability, at some point, after chaotically spinning around they will all slingshot each other away.

Of course, I don't know the details, and I suck at physics, so there's no way I'm going to try ;) :lol:

Eat this physicists :P

[Bobandirus]

In that case, HJVL, how do mathematicians have no way of coding how ants/termites work in a colony, yet a first year essay of mine is all about their behavior :P

And also, who cares about purity? The more interesting stuff should be the stuff that you do?

This sort of stuff. I would love to see as close as we can get to a whole world one.

[daveb]

while waiting for the bottom up understanding to follow later.

bottoms up!

[A Long Time Ago]

And also, who cares about purity? The more interesting stuff should be the stuff that you do?

I am a firm believer in this.

[michaeld]

I agree with Joe's purity diagram - except it omits all those pesky logicians to the right of the mathematicians!

[michaeld]

This was an interesting twist in the already multifaceted thread.

Perhaps we might start a physics thread. We never even began to discuss String Theory, Loop Quantum Gravity, or E8.

Yes good idea! I still think we need an asexy string theory book club.

Has anyone else looked at these tomes?

(723pp + 778pp).

Cool covers, and very reasonably priced, but I should warn anyone interested that they are extremely hard going - even by mathematical physics standards.

Maybe we'd do better by reading or re-reading Polchinski - not that this is at all easy either. Even though it was originally published over 12 years ago, and doesn't contain important new developments such as the AdS/CFT correspondence or the KKLT mechanism, it's still the principal authoritative reference.

The first of its 2 volumes is devoted to the bosonic string with the second volume covering the superstring. I admit I haven't actually read most of the second volume (though I do know some superstring theory from Green, Schwarz and Witten - the definitive pre-Polchinski reference - and other sources) but I could do with a refresher even on Vol. I.

EDIT: All right, I've made a new thread. If the admods think it's a good idea they could maybe move the relevant posts there. I suggest everything from Post 2776 onwards excluding 2797, 2814, 2815.

[michaeld]

Some of us somewhat derailed the P & Serafine are engaged thread with our science discussion - sorry P & Serafine! So anyway I thought I'd make a new thread for continuation of that topic. Perhaps some of the posts could be copied over - that's up to the Admods. Watch this space!

So yeah anyway. String theory is the next topic. Who's up for reading or re-reading Polchinski?

[Kelly]

Thanks for the new thread.

We could let these beautiful physics posts remain here and grace the P&S thread (it adds awesomeness).

I found some graduate-level math difficult (and some not, but I would be rusty with it). I even made a C in Statistical Mechanics (something like determining thermodynamics of large-scale scenarios by utilizing quantum mechanics and then intergrating over extremely large values).

But I should brush up on graduate maths. I need to.

I troubleshoot particle accelerators for a living (usually running at less than 1 million eV), and my work does not really require anything above elementary calculus (my mind is a-wastin'). :redface:

I envy physicists with more challenging careers.

[Kelly]

I have neither Quantum Fields and Strings: A Course for Mathematicians nor Polchinski's String Theory, Vol. 1 : An Introduction to the Bosonic String, or any of the second volumes of each (shows how out of touch I am). But I am willing to dip my toe into the discussion and hope that I can contribute.

[------]

I'm more interested in discussing that comic with purity, Maths on the right and everybody else lined up.

http://math.sfsu.edu/beck/images/xkcd.purity.png

I wonder where language and philosophy would come into both of those. I mean you get philosophy of maths and philosophy of language (and language of philosophy) - can you get biology of maths?

Surely psychology is more about chemistry which happens in the brain - but how does that make it biology? Is sex really just applied chemistry?

SCIENCE OFFICER SPOCK! GET IN HERE! I HAVE STUPID QUESTIONS TO ASK!

[Næt.]

Sex is applied genitals.

[Kelly]

I did just order Superstring Theory: Volume 1, Introduction by Green, Schwarz, and Witten.

*awaits arrival*

[Næt.]

Physics makes my head hurt. I prefer biology.

*eyes his copy of The Ancestor's Tale*

[michaeld]

RE: ordering GSW.

Oh OK cool. It's from the 80s so doesn't contain anything about the second superstring revolution (D-branes, dualities, M-theory etc.) but it's still a classic. It also has more detail than Polchinski about certain topics, for example the Green-Schwarz superstring. (That's the model with classical spacetime supersymmetry, as opposed to worldsheet supersymmetry, though the quantization in GSW only proceeds via the lightcone. Manifest super-Poincaré spacetime supersymmetry is much harder to quantize though it is possible, as the recent work of Berkovits shows.)

[Bobandirus]

Physics makes my head hurt. I prefer biology.

*eyes his copy of The Ancestor's Tale*

Hooray! Another biologist :)

I haven't ever heard of The Ancestor's Tale, but I would love to have Historica Animalium. Aristotle may have been badly wrong on some bits, but he was very good on some other bits, considering how long ago he was.

[------]

Sex is applied genitals.

Genitals is biology. So a biological action is pieces of biology tissue doing something. When do they think chemistry comes into this?

[Kelly]

RE: ordering GSW.

Oh OK cool. It's from the 80s so doesn't contain anything about the second superstring revolution (D-branes, dualities, M-theory etc.) but it's still a classic. It also has more detail than Polchinski about certain topics, for example the Green-Schwarz superstring. (That's the model with classical spacetime supersymmetry, as opposed to worldsheet supersymmetry, though the quantization in GSW only proceeds via the lightcone. Manifest super-Poincaré spacetime supersymmetry is much harder to quantize though it is possible, as the recent work of Berkovits shows.)

Hopefully, it can be a good introduction to the more hard-core tomes. But D-branes and M-theory are musts. Now that I have spent money on the first book, perhaps I can find one (either Quantum Fields and Strings: A Course for Mathematicians or the first Polchinski book) to get next.

*ponders which*

[michaeld]

Polchinski. The QFAS books are nice but a little wacky and not really mainstream.

GSW and Polchinski are the definitive string theory books but there are others that are less systematic but give a somewhat quicker guide to modern topics. Barton Zwiebach's String theory for undergraduates (or titled something very similar to this - can't be bothered to look it up) is a good one. There's also the book by Schwarz and the Becker sisters - a kind of modern update of GSW (though not a replacement for GSW). There's also String Theory Demystified by McMahon - quick and dirty but still very informative.

Also, regarding Polchinski, I should mention that he also has a shorter version of his book on his webpage: Joe's Little Book of String. Less comprehensive than the printed version (and actually I like the BRST stuff from the Big Book of String) but it gets to the point much faster.

EDIT: I should also mention, so there's no misunderstanding, that GSW is pretty hardcore. It's just it doesn't contain the important new contributions of the 1990s and beyond. It's still an irreplacably important book however.

[Næt.]

Physics makes my head hurt. I prefer biology.

*eyes his copy of The Ancestor's Tale*

Hooray! Another biologist :)

I haven't ever heard of The Ancestor's Tale, but I would love to have Historica Animalium. Aristotle may have been badly wrong on some bits, but he was very good on some other bits, considering how long ago he was.

You have nae heard of The Ancestor's Tale? I understood it to be quite well known.

Sex is applied genitals.

Genitals is biology. So a biological action is pieces of biology tissue doing something. When do they think chemistry comes into this?

I'm just making a joke D:

[Kelly]

Physics makes my head hurt. I prefer biology.

Due to your present name, methinks that you have at least watched a few episodes of The Big Bang Theory. ;)

[------]

Sex is applied genitals.

Genitals is biology. So a biological action is pieces of biology tissue doing something. When do they think chemistry comes into this?

I'm just making a joke D:

Perhaps but it was truth and I still demand an answer from some chemist ( what do they call themselves? Chemistrist... chemist...)

I NEED A SCIENCE OFFICER!

(*goes back to watching Star Trek*)

[Kelly]

To get started, I suppose I can introduce peeps to String Theory by posting my myopic view of it.

All elementary particles (such as electrons and quarks) are strings, and what makes them different from another is the way that they vibrate. We think of strings as looking one-dimensional, but in reality, these strings can be in more dimensions.

Our universe itself is on a 3-dimensional brane (think of membrane), with another of time. These are in an 11-dimensional matrix. Our universe has 11 dimensions (or 26, and yes, String Theory requires 10 dimensions, but M-Theory requires 11).

The strings are attached to the 3-D brane of the universe, and cannot leave the universe. All of your electrons and such that make up you, our earth, and galaxies are bound to this membrane. You can't leave. But there are certain particles that can, namely, gravitons. They are closed strings, and are not attached to the brane. So, they can leave. And the reason why gravity is so much weaker than the other three forces is that they are not attached, and give a greatly decreased net force.

Such gravitons can leave our brane and affect other branes (parallel or near-parallel universes). And gravitons from them can affect our universe. Indeed, gravity from galaxies in nearby universes can account for dark matter—places where we see gravitational effects from a place in space yet we do not see any detectable matter there.

Anyway, every elementary particle is a string, vibrating in many dimensions, and reactions between particles depend on the way that they are vibrating. Strings can join and they can split—particles can decay (split) or be created.

The math involved in String Theory physics can be fun and complicated. I hope to learn much via this thread. I also need to start reading.

The philosophy may be more interesting and stimulating.

Let's get started. :)

[Bobandirus]

Physics makes my head hurt. I prefer biology.

*eyes his copy of The Ancestor's Tale*

Hooray! Another biologist :)

I haven't ever heard of The Ancestor's Tale, but I would love to have Historica Animalium. Aristotle may have been badly wrong on some bits, but he was very good on some other bits, considering how long ago he was.

You have nae heard of The Ancestor's Tale? I understood it to be quite well known.

No idea why I didn't know about it. Just never came across it I guess. Next time I stumble into Waterstones, Ill have a look.

[vmg15]

Perhaps but it was truth and I still demand an answer from some chemist ( what do they call themselves? Chemistrist... chemist...)

I NEED A SCIENCE OFFICER!

(*goes back to watching Star Trek*)

Chemist is the correct term. And I'm not entirely sure what you're asking.

Whenever there is biology, there is chemistry. Biology is applied chemistry, chemistry is applied physics, and physics is applied mathematics.

You say genitals are pieces of biological tissue. This is true. Chemistry allows tissue to exist. It allows atoms to form compounds, to form molecules, to give rise to macromolecules and more specifically the biopolymers (lipids, carbohydrates, proteins, and nucleic acids) that are the building blocks of life - of biological tissue.

You also say that sex is a biological action. This is also true. Biological actions directly rely on chemistry. They rely on chemical reactions. Everything we think, everything we do, even our own LIFE, is dependent on these reactions. They are so fundamental it is impossible to summarize every which way they are involved in "biological actions". From being sentient beings, to being sexual, to performing all the physiological aspects of sex... Chemistry is behind it.

And then think... Physics is behind every aspect of chemistry.

The world truly is a complex yet beautiful thing.

[Bobandirus]

Whenever there is biology, there is chemistry. Biology is applied chemistry, chemistry is applied physics, and physics is applied mathematics.

And yet maths cant do crap all on modeling ant behavior AFAIK?

[Henny]

*applies ink ribbon with the words "read, but not understood"*

Carry on. :P

[Bobandirus]

*applies ink ribbon with the words "read, but not understood"*

Carry on. :P

If that was at me, yep. I realized. :redface: I was never the best at that sort of thing.

[Henny]

*applies ink ribbon with the words "read, but not understood"*

Carry on. :P

If that was at me, yep. I realized. :redface: I was never the best at that sort of thing.

Nah, it was this thread in general.