Quantum theory and relativity: The science part.

Summary:

We concentrate here on the science part of quantum mechanics and relativity, and this includes real maths. NO philosophical discussion here unless you base it on real hard facts with maths and numbers!

Quantum theory and relativity: The science part.

obaeyens 20 Nov 2010 00:20

Some people have learned about the LHC, so many people have questions about quantum mechanics/relativity and probably want to learn it.

I myself have been learning about theory of relativity because one history teacher claimed that we were not intelligent enough when I was 15 years. So that triggered me to read many books, but it stayed more philosophically.

I stared with books like the “Cosmic code”, later “The fabric of the Cosmos” by Brian Greene and finally “Warped passages” by Lisa Randal.

I even bought a quantum mechanics book to learn the math but got stuck the math pretty fast.

It all changed when I found these books:
“Quantum mechanics demystified” by David McMahon.
“Relativity demystified” by David McMahon.

The relativity demystified actually made me understand why I failed to understand quantum mechanics since I lacked part of my math skills, so I went off to get the other books.
“Supersymmetry demystified” by Labelle.
“Quantum field theory demystified” by David McMahon.
“String theory demystified” by David McMahon.

In NO way do I claim to understand the quantum mechanics! But I am willing to learn and I hope that on this thread we can discuss the math part and learn from each other. With a bit of luck we can then convert this knowledge to LHC typical questions to debunk the end of the world.

In the worst case only Emmylou will post here.

Re: Quantum theory and relativity: The science part.

emmylou 21 Nov 2010 00:19

omg obaeyens thank you for this thread :)

ok so let me tell you a bit about how i got into quantum mechanics, I am a great believer of String Theory sadly this involves a lot of QM I have a fantastic book called the Elegant Universe bu Brian Greene I had to leave it because it was to complicated for me, so I thought ok i have avoided this way to much time to try and get to grips with it or at least try, so off I went to the book shop and I bought myself In Search of Schrodinger's Cat by John Gribbin.

So far it's ok says that all you really need is an open mind I have that :) so QM is the world of the very small where everything gets turned on it's head and nothing seems to be what it should be? he says that if you have a cat in a box you have no idea if the cat is dead or alive because you have to look inside the box to make sure but even then you can't be sure if what you are seeing is real or not hmmm.

Anyways as you know I am a huge follower of the LHC wha better excuse to learn one of he most complicated things in physics :D I can not understand the maths much at all this is what gets to me sometimes because i don't think i can come to grips with it fully until i know some more maths, obaeyens i will have a look for he books you listed :) have you read or heard of the Road To Reality by Roger Penrose? huge book and it's pure maths but it could be a good referance book.

Look forward to having some good discussions with you about this :) though i am quite slow on the up take sometimes I am sure i will manage, you seem intelligent to me by the way :) this time last year i never in a million years thought i would be having conversations like this ;) anything is possible when you want to learn and have sure passion for a subject ;)

Emmy

---

Learn from yesterday, live for today, hope for tomorrow. The important thing is not to stop questioning.
Albert Einstein

Re: Quantum theory and relativity: The science part.

obaeyens 21 Nov 2010 01:45

I am a huge favourite of string theory, BUT, string theory is at this moment unproven and I have absolutely no problem to put it into the garbage bin if it turns out to be false.

I do love the philosophical consequences of string theory but if you want to do science then you have to follow the facts, not the emotional logic.

The demystified books, even though you might not understand the maths just skim through them, you will discover stuff that you did not realize yet. For example a rotating black hole has 2 event horizon's!

Re: Quantum theory and relativity: The science part.

obaeyens 20 Nov 2010 00:33

Something about the light-speed I realized when I started to understand the math part is that my interpretation of the limit of lightspeed in vacuum was wrong.

I was always comparing to an human understandable equivalent of a car travelling at light-speed, but that is completely wrong interpretation. Fact is that the universe is built around this light-speed, it is a property of this universe.
The second part of the missing link is that all mass wants to move at light-speed instantly but something is preventing it slowing it down like it has to go though mud. yes the Higgs boson.

Re: Quantum theory and relativity: The science part.

RickardM 21 Nov 2010 01:46

I have to agree with emmylou here obaeyens, this has the potential to be one quite interresting thread=)

I think that my interrest for physics in general, and QM in particular, started out the same way as emmylou's did, with the discovery of the fantastic (and sometimes scary) science behind the LHC and RHIC. To begin with it was kind of like a hate-love relationship between me and physics, because I felt more or less compelled to learn and understand things as fast as I could (note to self; OCD does marvelous things to reading comprehension). Now I've managed to set the pace to a more reasonable level and thus am able to enjoy the beauty of how things work on a more detailed level than before. But just like quite a few people over here my interrest for QM has been focused on the philosophical aspects of the aforementioned field.

Schrödingers cat, now that's the kind of thinking that can drive you insane; since there is a 50% chance that the cyanide has killed the cat, and 50% that it hasn't, the cat must be considered to be both dead and alive untill you open the box and see the result, right?

Have you guys read Gödel, Escher, Bach - Eternal Golden Braid by Douglas R Hofstadter? If so, what did you think of it?

---

Facts are stubborn things.
- Ronald Reagan

Last edited on 21 Nov 2010 01:46 by RickardM Show more

Re: Quantum theory and relativity: The science part.

obaeyens 21 Nov 2010 02:20

If I had more time then I would read it all :-)

Yes quantum mechanics have its way to make you insane when you look at the philosophical consequences.

But first things first.
I somehow got puzzled a long time between quantum mechanics version of gravity and the theory of relativity. One is exchanging gravitons the other bending space. It is not conflicting at all, just 2 different viewpoints.

The important thing to understand is what we call laws of physics is nothing more that a model or simplification of what the universe is really like. The universe does not care about the laws of physics. The laws of physics is a human invention that models this universe pretty good. Some models work best at large scale like relativity theory, some works best at small scale like gravitons.
You can basically see this as a metro map and a street map. Both street maps and metro maps are simplified versions of the real city but helps us a lot to understand the city and to get us somewhere.

The same is true for Newton's model of gravity. It is not wrong, it is still being used by NASA space travel, but the relativity models is more accurate in all situations but also requires more calculations which might not be important for slow space travel like going to Mars.

Re: Quantum theory and relativity: The science part.

emmylou 21 Nov 2010 02:25

Rickard :)

You have got it spot on with Schrodingers Cat hurts my head just thinking about it lol.

I have to say I agree with you when you say you wanted to learn everything fast I have that much i want to learn and it seems it takes ages to get your head around things, I have always stayed clear of QM but at the back of my mind I have always thought that it would be worth a shot even if it does take ages to get it sorted in my head :)

You will both have to be patient with me at times as i tend to ramble sometimes especially when I have been reading and need to get things outta my head :)

So as far as I understand QM is the real physics of everything without this we would know nothing, I think QM scares people because it is hard and complex but to be honest I am really looking forward to learning and we can help each other along the way :)

Rickard I have not read that book, will write it on my book list for the next time I go shopping :)

Emmy

---

Learn from yesterday, live for today, hope for tomorrow. The important thing is not to stop questioning.
Albert Einstein

Re: Quantum theory and relativity: The science part.

obaeyens 21 Nov 2010 02:49

Don't worry about rambling emmylou, a learning process means making mistakes.

Once I thought that ainti-matter would mean anti-gravity. Boy was I wrong. LOL

QM scares people because it has been taken out of context big time by quacks scaring people.
I actually doubt that it is hard once you understand the maths part. The deeper I get into it the more it makes sense without the head spin.

Re: Quantum theory and relativity: The science part.

emmylou 21 Nov 2010 02:58

Thanks :)

How are you getting on with the maths? me and maths have a very love hate friendship LOL,

I think with most people physics in general scares people, which is really bad because it's awesome :) I really need to get more maths practice in :D I ain't picked the most easy subject in the world to teach myself LOL ;)

---

Learn from yesterday, live for today, hope for tomorrow. The important thing is not to stop questioning.
Albert Einstein

Re: Quantum theory and relativity: The science part.

obaeyens 22 Nov 2010 23:56

Sorry for the delay in answering, my internet drops out the last few days, and I somehow he he's been stable for the last 30 minutes now. Tomorrow a technician will have to come.

I have a hard time to grasp the Quantum mechanics maths. Too abstract but I am getting deeper into it.
And I am not used to the English words, so I still don't know what "Conjugate" means.

They have something like this |X> This is what they call a "ket", and actually represents a vector infinite dimensions.

They have also this <Y| notation which they call a "bra". This is the Conjugate vector of the |Y>

And here comes the cool part they combine it <Y|X> which the call a "bra-ket" and is defining a dot-product vector (2 dimensional vector space) but in infinite space a.k.a Hilbert space.
We know one example of Hilbert space: Euclidean space which is a subset of Hilbert space aka our 3D space x,y,z vectors: x+yi+zk

Last edited on 23 Nov 2010 00:18 by obaeyens Show more

Re: Quantum theory and relativity: The science part.

obaeyens 23 Nov 2010 00:15

The spin of a particle is detected in the Stern-Gerlach experiment.

He had a North and South pole magnet pointing to each other creating a magnetic field.
Now he fired neutral particles through the split and half the particles went up and the other half went down.

What was expected was a continuous spread of particles when they reach a target at the other side but that did not happen. They got 2 determined up and down beam. So the spin clearly demonstrated a quantized spin. It is called spin-up (+1/2) and spin down (-1/2)
The 1/2 because it can be only 2 states.

Again you find the kets
Spin-up : Sz|+> = h_bar/2 |+>
Spin-down : Sz|-> = h_bar/2 |->

Where h_bar is a special form of Planck constant.
h=Planck constant
h_bar = h/(2*pi)

When I learn more I will add. I hope this starts to make you more interesting in the maths.

Last edited on 23 Nov 2010 00:15 by obaeyens Show more

Re: Quantum theory and relativity: The science part.

obaeyens 23 Nov 2010 00:30

Another key element to understanding quantum mechanics is the black body radiation.
The black body radiation has this typical curve, and if you know that an integral can calculate the surface under the curve (aka energy) to extreme accuracy then you are tempted to use that integral.
But there is a problem, the energy becomes infinite if you calculate for all frequencies. Which is impossible in reality.

Planck discovered that energy does not come in a continuous spread but in discrete intervals (quantum energy). This interval is the Plancks constant!

Instead of calculating the surface of the black body radiations with a integral you must calculate it with a summation.

The basic quantum of energy = epsylon = hv (plancks constant times frequency)

So this is how they discovered the quanta in energy and quanta in spin.

Re: Quantum theory and relativity: The science part.

emmylou 23 Nov 2010 01:05

obaeyens

no problem pleased you are back though ;)

Ok I have been kinda looking into the whole maths side of things for awhile, i think i am scared because with me not doing all that in school i am sarting from scratch, i am also very shy about asking questions especially if i will make me sounds silly but here goes :)

So basically it's everything physics is based around? does space-time come into it? I know that space is curved, I also know that Enistien had a big problem with this, I just feel like giving up before i have even really started *blushes*

Maths has always scared me but i find i can read what equasion should be, like i can read some of the stuff that the LHC do :) I just can't get it to click in my head how we can know so much by numbers. I think this is gonna be my main problem when it comes to QM.

---

Learn from yesterday, live for today, hope for tomorrow. The important thing is not to stop questioning.
Albert Einstein

Last edited on 23 Nov 2010 01:08 by emmylou Show more

Re: Quantum theory and relativity: The science part.

obaeyens 23 Nov 2010 01:18

Don't worry about questions. ;-)
I have the same problems you are facing, but the demystified series seems very good. Especially when I reread, reread, reread…. It is like learning a language.

Keep the Planck constant in mind. Especially the one divided by 2 times pi! This one comes back a lot.

LHC really makes sense when you get used to the math. Even if it is just basic.

Relativity comes into play at QM in the form of time dilation and also the mass increase of the particles accelerated. I would start with the relativity theory first, that is the easiest start to get used to the maths.

Re: Quantum theory and relativity: The science part.

emmylou 23 Nov 2010 01:28

:)

Thanks I will have a look into that tonight I did get a book you can read online its called an introduction into quantum Mechanics :) it's umm interesting that gives me Planck stuff :) hard but workable :)

ok off to study Relatvity theory :D i might have loads of questions after :D thanks again.

---

Learn from yesterday, live for today, hope for tomorrow. The important thing is not to stop questioning.
Albert Einstein

Re: Quantum theory and relativity: The science part.

obaeyens 23 Nov 2010 01:31

ohhhhh noooooo what have I done? ;-)
I created a Monster! LOL

Re: Quantum theory and relativity: The science part.

obaeyens 23 Nov 2010 01:38

About relativity theory. I give you a big clue:
I knew when I was young that the 4th dimension was time. But had a hard time to put a unit on it.

It is surprisingly simple.
x,y,z are distances we use meters.
but t = time, so unlike distances meters!

Here comes the clues= distance = speed x time
Now guess what this "speed" is?

Yep the magic number c = speed of light!

So the 4 dimensions are
{ct,x,y,z} ;-)

Re: Quantum theory and relativity: The science part.

emmylou 23 Nov 2010 07:04

obaeyens

I dunno if you have watches these lectures? if not give them a go when you have time they are done by Leonard Susskind. I have read why does E=mc^2? that helped alot though i think i will have to look through it again at some point lol.

I could never be a monster :P i am to nice for all that hehehe

[http://www.youtube.com/watch?v=pyX8kQ-JzHI]

---

Learn from yesterday, live for today, hope for tomorrow. The important thing is not to stop questioning.
Albert Einstein

Re: Quantum theory and relativity: The science part.

obaeyens 23 Nov 2010 13:48

Yes I started to see these lectures! They are wonderful.
Just a lack of time to watch them all.

Re: Quantum theory and relativity: The science part.

emmylou 23 Nov 2010 18:32

Omg I know some of them are so long :O
good thing I have plenty of time at night to sit and listen to them, very easy to listen to though he explains things really well, I am only gonna be on lecture 2 tonight but thats ok, slow is good as they say :D

---

Learn from yesterday, live for today, hope for tomorrow. The important thing is not to stop questioning.
Albert Einstein