Quantum physics.

[BetaNumeric]

Everything . All of chemistry is quantum mechanics, and from that everything you have ever come in contact with is essentially quantum mechanics.

All biology is really chemistry, all chemistry is really physics and all physics is written using mathematics. Hence why mathematicians are god..... err... I mean God thinks he's a mathematician

"Anyone who is not shocked by quantum mechanics has not understood it" - Niels Bohr (I think)

At least initially. After a while you just get used to it, as well as developing a feel for things.

Last week in the office we were looking at some quantum mechanics and part of the problem was that something involved summing up a lot of terms, so many terms of such a type that the sum is infinite. Problem? Nah, that happens all the time. The main issue in all the literature on it was how to make sense of that infinite sum. I didn't bat an eyelid, quantum field theory is awash with such things.

For instance, I imagine most of you have heard how string theory says there's extra dimensions, right? The way it is done is a certain expression needs to be zero and the expression depends on the dimensionality of space-time. It also depends on the sum 1+2+3+4+5+....... (otherwise known as Zeta(-1), where Zeta is the Riemann Zeta function). What do string theorists when they add up all the natural numbers? -1/12. And that is why string theory has 10 dimensions, since the equation is (if memory serves) (1+2+3+4....)(d-2) + 2/3 = 0, so if (1+2+3+4....) = -1/12 you have d=10.

Of course it's a little more subtle than that and anyone familiar with the Zeta function from complex analysis will know that the residue of Zeta(z) at the singularity z=-1 is -1/12 but it's still a 'double take' moment when first you see it.

Brayne... exploded

Do you mean brain or brane?

It also postulates 11 dimensions, if you want to start moving into string theory.

Supersymmetric string theory is a fundamentally 10 dimensional theory (ignoring subcritical models). The extra dimension is in M theory and its origin is buried deep within Type IIA string theory and its lack of an S dual. The existence of the 11th dimension is non-trivial, it took a decade before Witten even realised it. Dualities in string theory happen to be an 'interest' of mine

 

[lixxus]

It also postulates 11 dimensions, if you want to start moving into string theory. It also looks at different universes as being a membrane and rubbing next to each other or if you really want to go hardcore, have a look at is our universe a hologram:

just theory not proven scientific fact.

 

[bluesouljah]

Yeah, theoretical physics, but at a quantum level, you have to deal with probabilities anyway, so, it's all theory to some degree.

 

[Cr0fty]

I've just started reading this... http://www.amazon.co.uk/gp/aw/d/057123545X/ref=redir_mdp_mobile/277-6295025-0085218

Physics is possibly the greatest thing we humans have to offer!

 

[bluesouljah]

Yeah, I started with this: http://www.amazon.co.uk/Elegant-Uni...8111/ref=sr_1_3?ie=UTF8&qid=1305236571&sr=8-3

It was given to me as a freebie somewhere and I ended up getting quite into it.

 

[BetaNumeric]

just theory not proven scientific fact.

Firstly you can never prove any model of the universe 'fact' because no amount of experiment will ever mean you've excluded all realms where the model might apply. You can only demonstrate a model is valid to a given accuracy in a particular domain.

Secondly 'theory' in science means an hypothesis which has been tested by experiment and it's passed. An as yet untested model is an hypothesis.

Thirdly 'string theory' should thus be called 'string hypothesis' but it doesn't roll off the tongue so easily. But things like the 'Newtonian laws of motion' of 'Laws of thermodynamics' shouldn't be called 'laws' either, they are not universally valid in all domains at all times. They should be called models or theories. In the case of Newtonian mechanics we know it to be wrong once you measure accurately enough, yet the name persists.

I might seem like I'm splitting hairs but the whole "It's only a theory!" thing comes up in regards to evolution a lot. Evolution, change over time in populations, is a fact. 'The theory of evolution by natural selection' is the model hypothesised to explain the observed variation and it has been tested and become a 'theory'. There is no higher 'rank' in science than theory.

 

[rpstewart]

Quantum Physics: The dreams that stuff is made of

 

[Rexton]

One of my college friends who has gone on to do his degree in quantum was reading books and researching from his early childhood, and basic stuff still leaves him clueless. Don't worry if you don't understand it.

 

[Sherbs]

Physics is possibly the greatest thing we humans have to offer!

I agree, so damn awesome.

I should have done Physics at uni.

=(

 

[PardonTheWait]

The documentary sherbs posted up was perfect, providing a general gist that a regular stupid person could understand.

I didn't want any more than that, just a notion of what it was! Some of the others posts were really useful as well, thanks

 

[|Thomas|]

All biology is really chemistry, all chemistry is really physics and all physics is written using mathematics. Hence why mathematicians are god..... err... I mean God thinks he's a mathematician

Hehe, it always reminds me of the xkcd comic: http://xkcd.com/435/ .

For instance, I imagine most of you have heard how string theory says there's extra dimensions, right? The way it is done is a certain expression needs to be zero and the expression depends on the dimensionality of space-time. It also depends on the sum 1+2+3+4+5+....... (otherwise known as Zeta(-1), where Zeta is the Riemann Zeta function). What do string theorists when they add up all the natural numbers? -1/12. And that is why string theory has 10 dimensions, since the equation is (if memory serves) (1+2+3+4....)(d-2) + 2/3 = 0, so if (1+2+3+4....) = -1/12 you have d=10.

Of course it's a little more subtle than that and anyone familiar with the Zeta function from complex analysis will know that the residue of Zeta(z) at the singularity z=-1 is -1/12 but it's still a 'double take' moment when first you see it.

I recently had an exam on infinite series, such things still make my head bleed . Honestly how can the order of summation matter? Crazy mathematicians . In a slight tangent, for anyone who thinks QM doesn't make sense:

1 - 1/2 + 1/3 - 1/4 + 1/5 - ... = Log(2) (roughly 0.69)
1 + 1/3 - 1/2 + 1/5 - 1/4 + ... = 3Log(2)/2 (roughly 1.04)

Swap the numbers and you get a different number... :/

 

[Landy]

I think i just had a brain aneurysm

 

[BetaNumeric]

Quantum Physics: The dreams that stuff is made of

Unfortunately flat out wackos like the film "What the Bleep Do We Know" cash in on the pseudo-scientific approach to quantum mechanics, claiming that the universe is literally made up of our perception and by wishing real hard we can bend reality to our whims.

I recently had an exam on infinite series, such things still make my head bleed . Honestly how can the order of summation matter? Crazy mathematicians . In a slight tangent, for anyone who thinks QM doesn't make sense:

1 - 1/2 + 1/3 - 1/4 + 1/5 - ... = Log(2) (roughly 0.69)
1 + 1/3 - 1/2 + 1/5 - 1/4 + ... = 3Log(2)/2 (roughly 1.04)

Swap the numbers and you get a different number... :/

That's because the series is not absolutely convergent, ie the sum a_{1} + a_{2} + .... only converges in an order independent way if the sum |a_{1}| + |a_{2}| + .... converges. If you remove all the - signs from your expression you have the harmonic series, 1/1 + 1/2 + 1/3 + ...., which doesn't converge. Thus the order is important.

A more striking example is 1 - 1 + 1 - 1 + 1 - 1 + .... Is it (1-1) + (1-1) + (1-1) + ... = 0 + 0 + 0 + ... = 0 or is it 1 + (-1 + 1) + (-1 + 1) + .... = 1 + 0 + 0 + .... = 1? In that case the summation isn't defined. In some cases you can start getting into things like Abel summations, which can make sense of things like 1 + 2 + 4 + .... in the same way 1+2+3+.... can be made to make sense in some way.

 

[Shayper]

Quantum Physics is literally redefining pretty much everything to do with with physics.

I am a bit too drunk to be going into detail, but it completely threw a large part of classical physics (high school stuff) out of the window, as that suggests that everything that happens in the universe is preordained to happen, whereas quantum physics introduces the element of randomness.

A good example is the model of the atom with electrons whizzing around everywhere, but in a defined orbit (the Rutherford model). What scientists have actually discovered is that the measure of electrons as we know them is actually a measure of the density of a charge at any given moment, and that in the next infinitely small moment the charge could be dissipated, or completely somewhere else, but that the average charge density is what defines the atom. There are still electron shells and the like but not in the GCSE sense

Another example is the recent success in teleporting a ray of light. Photons are very similar to an electron in the way that they have a negligible mass (in this case it is almost entirely comprised of energy, but as Einstein taught mass can be directly converted to energy and vice versa) and exist everywhere at any given time (should have included this bit with the electrons - damn you alcohol!), but as soon as we try to measure them we actually affect them in such a way that suddenly they are in one place and have mass.

As far as I have read anyway, I could be completely wrong but hey.

I love high end physics, used to annoy my A-Level physics teacher no end by constantly asking questions about things like dark matter, singularity and quantum physics

 

[BetaNumeric]

A good example is the model of the atom with electrons whizzing around everywhere, but in a defined orbit (the Rutherford model). What scientists have actually discovered is that the measure of electrons as we know them is actually a measure of the density of a charge at any given moment, and that in the next infinitely small moment the charge could be dissipated, or completely somewhere else, but that the average charge density is what defines the atom. There are still electron shells and the like but not in the GCSE sense

It is not a measure of charge density, it is a probability amplitude measure. Viewing it as a charge density implies you're almost smearing, literally, the electron about a region and you could measure parts of its charge to be here or there or in that region or this region. Doesn't work like that. When you do the measurement to ask "How much charge is in this little region?" you either get all of the electron or none. However, if you keep doing the measurements again and again and again, thousands, millions of times, then you'll find the distribution of results is as if the electron is all over the place and behaving like some kind of fluid, diffracting and flowing.

The best example of that is the double slit experiment, which manifestly shows the effect measurement has on the system. Or the quantum Xeno effect, where a watched (quantum) pot literally doesn't boil.

Another example is the recent success in teleporting a ray of light. Photons are very similar to an electron in the way that they have a negligible mass

Electrons have a small mass but they definitely have rest mass. A photon has zero rest mass. The electron's rest mass is about 9 x 10^-31 kg while the upper limit on the photon mass via experiment is around 10^-51 kg, 100 million trillion times smaller. On theoretical grounds (U(1) gauge symmetry) the photon should have exactly zero mass.

(in this case it is almost entirely comprised of energy, but as Einstein taught mass can be directly converted to energy and vice versa)

It's important to realise what Einstein's equation actually said. It is often quoted as E=mc^2 but this is not valid for things with zero rest mass. The full equation (when you get units so c=1) is E^2 = m^2 + p^2, where p is the 3-momentum of the object. If the object is at rest p=0 and you get E=m but if m=0 then you get E=|p|, which also tells you that if the object has no rest mass (like photons) then it cannot be made to be at rest, else you'd have m=p=E=0.

 

[RomanNose]

It is not a measure of charge density, it is a probability amplitude measure. Viewing it as a charge density implies you're almost smearing, literally, the electron about a region and you could measure parts of its charge to be here or there or in that region or this region. Doesn't work like that. When you do the measurement to ask "How much charge is in this little region?" you either get all of the electron or none. However, if you keep doing the measurements again and again and again, thousands, millions of times, then you'll find the distribution of results is as if the electron is all over the place and behaving like some kind of fluid, diffracting and flowing.

The best example of that is the double slit experiment, which manifestly shows the effect measurement has on the system. Or the quantum Xeno effect, where a watched (quantum) pot literally doesn't boil.

Electrons have a small mass but they definitely have rest mass. A photon has zero rest mass. The electron's rest mass is about 9 x 10^-31 kg while the upper limit on the photon mass via experiment is around 10^-51 kg, 100 million trillion times smaller. On theoretical grounds (U(1) gauge symmetry) the photon should have exactly zero mass.

It's important to realise what Einstein's equation actually said. It is often quoted as E=mc^2 but this is not valid for things with zero rest mass. The full equation (when you get units so c=1) is E^2 = m^2 + p^2, where p is the 3-momentum of the object. If the object is at rest p=0 and you get E=m but if m=0 then you get E=|p|, which also tells you that if the object has no rest mass (like photons) then it cannot be made to be at rest, else you'd have m=p=E=0.

You might be able to answer my child like question, in the double slit experiment what would count as an observer? Would the wave function still collapse if there was someone looking away in the same room?

 

[Shayper]

It is not a measure of charge density, it is a probability amplitude measure. Viewing it as a charge density implies you're almost smearing, literally, the electron about a region and you could measure parts of its charge to be here or there or in that region or this region. Doesn't work like that. When you do the measurement to ask "How much charge is in this little region?" you either get all of the electron or none. However, if you keep doing the measurements again and again and again, thousands, millions of times, then you'll find the distribution of results is as if the electron is all over the place and behaving like some kind of fluid, diffracting and flowing.

The best example of that is the double slit experiment, which manifestly shows the effect measurement has on the system. Or the quantum Xeno effect, where a watched (quantum) pot literally doesn't boil.

Electrons have a small mass but they definitely have rest mass. A photon has zero rest mass. The electron's rest mass is about 9 x 10^-31 kg while the upper limit on the photon mass via experiment is around 10^-51 kg, 100 million trillion times smaller. On theoretical grounds (U(1) gauge symmetry) the photon should have exactly zero mass.

It's important to realise what Einstein's equation actually said. It is often quoted as E=mc^2 but this is not valid for things with zero rest mass. The full equation (when you get units so c=1) is E^2 = m^2 + p^2, where p is the 3-momentum of the object. If the object is at rest p=0 and you get E=m but if m=0 then you get E=|p|, which also tells you that if the object has no rest mass (like photons) then it cannot be made to be at rest, else you'd have m=p=E=0.

Aww... knew I would get done over for my lack of complete in depth knowledge... Betanumeric you sound like a very, very clever guy

 

[|Thomas|]

That's because the series is not absolutely convergent, ie the sum a_{1} + a_{2} + .... only converges in an order independent way if the sum |a_{1}| + |a_{2}| + .... converges. If you remove all the - signs from your expression you have the harmonic series, 1/1 + 1/2 + 1/3 + ...., which doesn't converge. Thus the order is important.

A more striking example is 1 - 1 + 1 - 1 + 1 - 1 + .... Is it (1-1) + (1-1) + (1-1) + ... = 0 + 0 + 0 + ... = 0 or is it 1 + (-1 + 1) + (-1 + 1) + .... = 1 + 0 + 0 + .... = 1? In that case the summation isn't defined. In some cases you can start getting into things like Abel summations, which can make sense of things like 1 + 2 + 4 + .... in the same way 1+2+3+.... can be made to make sense in some way.

Indeed it is , I thought I'd throw that one out there for the non-mathematicians amongst us. It still screws with my mind a little bit though .

You might be able to answer my child like question, in the double slit experiment what would count as an observer? Would the wave function still collapse if there was someone looking away in the same room?

The wave function is collapsed by the detector, not by humans in the room. If you automated the experiment and collected the data without anyone around you would get the same result.

 

[D.P.]

You might be able to answer my child like question, in the double slit experiment what would count as an observer? Would the wave function still collapse if there was someone looking away in the same room?

When physicists talk about observation they don't mean human observers, the environment is observing most things most of the time.

 

[masonkian]

watched them all last night

mind boggling