Getting my head around Astro Physics.

[renormalised (Carl)]

This will explain to you in simple terms why the 10-11 dimensions. If you run across any problems, post them here and either Steven or I will explain them for you

Supersymmetry

[Suzy]

[renormalised (Carl)]

It's not that bad!!!!

Geez, if I can understand that, then you should be able to

[CraigS]

Need a translator ??

[Jay-qu]

Hi Suzy,

If you are interested in string theory but dont have much of a background in maths, I would suggest picking up a book by Brian Green called "The Elegant Universe". Or if you prefer there is a documentary similarly named.

As far as I remember this book did not require much understanding of maths. Most pop-sci books on these subjects are fairly light on the details since since to go any deeper would require a degree for a start..

You have already taken the best step and that is to discuss things you dont understand with others, so keep that up and you will get there.

J

[sjastro]

Perhaps the best way of understanding String Theory without being bogged down in the mathematics is to understand the reason for it's existence.

Here is an introduction to String Theory in terms of the lead up theories
Special Relativity, General Relativity, Quantum Mechanics and Quantum Field Theory. The mathematics is only in passing. (Let the Physics and Applied Maths post grads do the suffering).

A few good lines in the presentation, add gravity to Quantum Field Theory and you get a train wreck.

http://www.slimy.com/~steuard/resear...o/slide01.html

Hope this helps

Regards

Steven

[snas (Stuart)]

Maybe there was a bit more anti-matter after all, and now because we're anti-matter, the real matter appears to be anti-matter?
(my head's hurting now....)

Rob, I've also wondered about this too. Who's to say that we are matter or antimatter. All we are is just that bit which exceeded its opposite at BB.

Steve and Carl, is it that simple? Or if we are really antimatter and not matter, does that fundamentally change the way things are for us? Do you have any comments.

Steve, I had a look at your link Steuard Jensen's discussion on String Theory. I've never been able to conceptualise the idea of any more than the 4 "obvious" dimensions, but his very simple explanation of the man and the ant walking on the tightrope allowed me to at least see how extra "invisible" dimensions may occur.

Stuart (biologist trying to be physicist )

[higginsdj]

Damn, you have jumped into the deep end. Here was I struggling with calculus and Solar System Dynamics thinking that was hard! Good luck.

If you want to improve your math and general physics, don't forget iTunesU. I've downloaded gigabytes of lectures and starting to make sense of derivitives, differential equations and integrations (well, just derivitives at this stage - I did fail maths at school - 30 years ago)

Cheers

[sjastro]

Originally Posted by snas

Rob, I've also wondered about this too. Who's to say that we are matter or antimatter. All we are is just that bit which exceeded its opposite at BB.

Steve and Carl, is it that simple? Or if we are really antimatter and not matter, does that fundamentally change the way things are for us? Do you have any comments.

There are four properties that differentiate matter from it's mirror image (antimatter).

(1) Charge
(2) Magnetic moment
(3) Parity
(4) Helicity or handedness.

Charge is obvious, parity and helicity relate to the mathematical symmetries of particles and antiparticles. So for example if a particles intrinsic spin and linear momentum are in the same direction then the particle has a positive helicity where as the corresponding anti particle will have the instrinsic spin and linear momentum in opposite directions (negative helicity). All neutrinos are left handed, all antineutrinos are right handed.

As far as an absolute test to differentiate matter from anti matter, the magnetic moment is the key. Even a particle with neutral charge such as a neutron has a magnetic moment.

If you pass a neutron through a magnetic field it will always deviate in the same direction in the field. The antineutron will deviate in the opposite direction. Same with the proton/antiproton.

We know we are made from matter, just break down the constituent nucleons that make up the matter pass it through a magnetic field and you have your answer.

Regards

Steven

[CraigS]

Originally Posted by sjastro

There are four properties that differentiate matter from it's mirror image (antimatter).

(1) Charge
(2) Magnetic moment
(3) Parity
(4) Helicity or handedness.

Charge is obvious, parity and helicity relate to the mathematical symmetries of particles and antiparticles. So for example if a particles intrinsic spin and linear momentum are in the same direction then the particle has a positive helicity where as the corresponding anti particle will have the instrinsic spin and linear momentum in opposite directions (negative helicity). All neutrinos are left handed, all antineutrinos are right handed.

As far as an absolute test to differentiate matter from anti matter, the magnetic moment is the key. Even a particle with neutral charge such as a neutron has a magnetic moment.

If you pass a neutron through a magnetic field it will always deviate in the same direction in the field. The antineutron will deviate in the opposite direction. Same with the proton/antiproton.

We know we are made from matter, just break down the constituent nucleons that make up the matter pass it through a magnetic field and you have your answer.

Regards

Steven

Is there a degree of conventionality in this ?
I guess if one applies tests for all of (1) to (4), then maybe there's no definitional issues (?)

… interesting ...

Cheers & thanks for a great answer, Steven .. very clear ..

[renormalised (Carl)]

I think in this case, Steven, their argument on matter/antimatter is more a difference of opinion on what you define as matter and antimatter. Being a case of philosophical semantics..."what do I think I am". "Antimatter" people might think they're ordinary matter and call us antimatter, which actually would be true from their point of view

[orestis]

Very Interesting topics Suzy,

I was thinking about how well all this technical stuff is communicated because i read and see scientists using all this technical jargon that we cannot understand but if they new how to break it down and explain it well then maybe we could understand.

Such as i was watching insight on SBS(i think) the other week or so and there was a Climate scientist in the studio taklking to a bunch of climate skeptics and he communicated very well and used Easy to understand analogys.

One of the best communicator was our beloved Carl Sagan,I only wish we had more like him now.

Regards Orestis

[renormalised (Carl)]

There are ways and means of breaking down the jargon into easy soundbites, but it can be difficult getting across the essential kernel of knowledge without diluting it that much it's basically useless to anyone. Lots of science gets misunderstood and misinterpreted because of this and it's where the public get led astray all too often.

[snas (Stuart)]

We know we are made from matter, just break down the constituent nucleons that make up the matter pass it through a magnetic field and you have your answer.

Steve, thanks for your answer. I see the beautiful "simplicity" to your answer. But then there is Carl's answer from a more philosophical standpoint which also has a certain simple beauty as well.

Hmmm, thanks guys, back to biology now.

Stuart

[sjastro]

Originally Posted by CraigS

Is there a degree of conventionality in this ?
I guess if one applies tests for all of (1) to (4), then maybe there's no definitional issues (?)

… interesting ...

Cheers & thanks for a great answer, Steven .. very clear ..

The conventionality in this case groups matter/antimatter into symmetrical pairings.

For example.

Protons/Antiprotons:- (1) and (2)
Neutons/Antineutrons:- (2)
Neutrinos/Antineutrinos:- (4)

For (3) If matter has +1 (or -1) parity then the corresponding antimatter has -1 (or +1) parity.

Regards

Steven

[sjastro]

Originally Posted by renormalised

I think in this case, Steven, their argument on matter/antimatter is more a difference of opinion on what you define as matter and antimatter. Being a case of philosophical semantics..."what do I think I am". "Antimatter" people might think they're ordinary matter and call us antimatter, which actually would be true from their point of view

Antimatter people are very much in the minority so their opinion doesn't count (isn't that how democracy works)

The fact that we can differentiate between matter and antimatter allows an argument on semantics.

It reminds me of a "discussion" I once had with a smart a*se know all kid who asked me how I could tell the difference between a piece of paper made of ordinary matter from and one made of antimatter. I said to him if you write your name on the ordinary piece of paper and looked in the mirror you would see a reversed image. Write on a piece of antimatter paper (and assuming you don't annihilate yourself in the process), the image isn't reversed. That completely confused him yet it was a subtle lesson of the role of parity in matter and antimatter.

Regards

Steven

[orestis]

Originally Posted by renormalised

There are ways and means of breaking down the jargon into easy soundbites, but it can be difficult getting across the essential kernel of knowledge without diluting it that much it's basically useless to anyone. Lots of science gets misunderstood and misinterpreted because of this and it's where the public get led astray all too often.

Very true Carl,
There a lot of times when this happens.Too often it seems on TV the media make all the science stuff too sensational.

regards orestis

[Jay-qu]

Originally Posted by sjastro

There are four properties that differentiate matter from it's mirror image (antimatter).

(1) Charge
(2) Magnetic moment
(3) Parity
(4) Helicity or handedness.

Charge is obvious, parity and helicity relate to the mathematical symmetries of particles and antiparticles. So for example if a particles intrinsic spin and linear momentum are in the same direction then the particle has a positive helicity where as the corresponding anti particle will have the instrinsic spin and linear momentum in opposite directions (negative helicity). All neutrinos are left handed, all antineutrinos are right handed.

Just to clarify this point a little.. You can have left and right handed electrons, just as you can have left and right handed positrons.

Neutrinos are an altogether different matter since it is no known if they are Dirac fermions (like electrons) or Majorana fermions. If they are Majorana fermions they would be their own anti-particles - like photons. The standard model of particle physics assumes neutrinos to be Dirac fermions.

Since the Weak force only interacts with left handed particles and right handed antiparticles and so if neutrinos are Majorana fermions then neutrinoless double beta decay would be possible.

This is all important because we know neutrinos have mass, but we dont know how to theoretically express the origin of their mass. Trying to use the Higgs mechanism (as is used to give all other particles mass) breaks gauge invariance - something held in very high regard amongst physicists. There are other mechanisms for explaining neutrino masses such as the see-saw mechanism, but it depends on the particulars of how many neutrinos there are and whether they are Majorana or Dirac fermions. A plus side to the see-saw mechanism is that it requires a heavy sterile neutrino which is a candidate for dark matter.

Hope I havent rambled too much..

[renormalised (Carl)]

Originally Posted by sjastro

Antimatter people are very much in the minority so their opinion doesn't count (isn't that how democracy works)


Regards

Steven

Yep, they all went off with a bang, years ago

Although minorities aren't supposed to be discriminated against in this day and age...figuratively speaking

[Suzy]

Originally Posted by Suzy

For instance, with string theory, they talk of 10 dimensions, but another source tells me 11.

Just found out the answer to this one.
The 11th dimension is TIME. 10 dimensions + time. Doh! The string theory model doesn't work with anything other than these 11 dimensions.

Thank you all, for your help and encouragment. I'm very grateful.