The Student Room Group

Scroll to see replies

It isn't if you don't understand it. If you understand it, it is quite logical so there aren't problems in understanding it.

Are you at Imperial studying or plan to go there?
Reply 2
Laugh sorry I saw this and thought it was a joke. I'll be taking Physics properly in a years time, but have learned a great deal about it from various sources, and I have to say if you find it easy then your perhaps the only person who has done so since the quantum revolution.

:laugh:

Physics is actually rated as the hardest subject in the US at least. On tables I've seen there are more students with higher SATS doing physics than Maths or Engineering, second and third respectively. They also score more highly in general, have higher drop out rates and according to the ability to test in some sort of accurate way physics is a tough subject.

If you find it easy well then you have a glowing career in physics ahead of you. AFAIK though you're the first person I've ever met on line or in person who has said this. And I frequent physics forums with some pretty well educated people and scientists. And I used to work in a medical physics department with a few PhD's and fellows in physics. And they didn't seem to think it was easy.
Reply 3
there is only one being for which physics is easy. Otherwise it's difficult
Reply 4
LOL, easy. Probably because they teach you the baby stuff in school.

Have you ever opened a physics textbook?
Try QM then try saying its easy.
Reply 6
saklut
I think he is talking about the physics a-level. I agree that it is very easy


Well he's in for a surprise at Uni then. Because A-level physics is nothing like as hard as the degree level stuff. I should know I've seen it. It's a whole new ball game, bit like the difference between GCSE and A-level Maths, and A-level Maths and degree level maths. A quantum leap, if you'll pardon the pun. :smile:

Probability of wave functions is quite complicated, and involves a fair bit of integral mathematics. And this is just the maths wait till you get a load of the superposition/wave function collapse side of the theory.

Unparseable latex formula:

$\mathbf{P}_{ab} = \int_{a}^{b} |\psi(p)|^2\, dp$



And the like.

This is just the ψ\psi

in a more general equation.

Unparseable latex formula:

$[br]\left[ - \frac{\hbar^2}{2m} \nabla^2 + V\left(\mathbf{r}\right) \right] \psi\left(\mathbf{r}\right) = E \psi \left(\mathbf{r}\right).[br]$



If that looks like a cake walk then your in for a smooth ride. :smile:
Reply 7
Looks easy to me :p:
Reply 8
edders
Looks easy to me :p:


Well if you have a degree then possibly, but was QM a doddle to learn? :smile:

Actually you're doing economics, I assume you did something similar at degree level? Is quantum mechanics that easy to explain? Most people have trouble getting their head around why a single photon creates and interference pattern in the Feynman two slit experiment. It involves wrapping your head around superposition.
are you smoking crack?
Sidhe
Well if you have a degree then possibly, but was QM a doddle to learn? :smile:



Yeah, tis a piece of piss, I picked it up over the weekend, don't know why Feynman caused such a commotion over it :rolleyes:

I'm now using Qm to analyze the structural composition of bran flakes, well, and mayonnaise, and we all know the relationship between Qm and mayonnaise....don't we? :wink: :p:
This thread seems to be a proof of the Imperial's superiority for Physics !
whitebuthotter posted this question in the imperial forum !!! xD
Reply 12
Oddjob39A
Yeah, tis a piece of piss, I picked it up over the weekend, don't know why Feynman caused such a commotion over it :rolleyes:

I'm now using Qm to analyze the structural composition of bran flakes, well, and mayonnaise, and we all know the relationship between Qm and mayonnaise....don't we? :wink: :p:


Oh pardon me I didn't realise you were studying mayonaisian mechanics. Obviously to someone with your advanced learning it's going to be a piece of piss. :wink::smile:

Heads up, don't forget to allow for the fact that bran flakes absorb particular wavelengths of both ultra and infra red in your equations. It makes the integrals come out with something a little more in line with experimentation. Most people tend to only factor in visible light.
Surely anyone who finds Physics too easy should just formulate a Grand Unified Theory and get on with something else in life?
Sidhe
Oh pardon me I didn't realise you were studying mayonaisian mechanics. Obviously to someone with your advanced learning it's going to be a piece of piss. :wink::smile:

Heads up, don't forget to allow for the fact that bran flakes absorb particular wavelengths of both ultra and infra red in your equations. It makes the integrals come out with something a little more in line with experimentation. Most people tend to only factor in visible light.


Well yes, it is rather!

I also picked up double dutch and high German, one has to keep oneself entertained afterall, especially seeing as the particle accelerator was in for the M.O.T. last weekend.

Ultra and infra equations duly noted.
Reply 15
Sidhe
Well if you have a degree then possibly, but was QM a doddle to learn? :smile:

I did a BSc in physics at Imperial :wink:
And actually I found QM to be a lot easier than say advanced classical physics. Possibly because the maths is quite straightforward.
ColinOfEdinburgh
Surely anyone who finds Physics too easy should just formulate a Grand Unified Theory and get on with something else in life?


I totally agree. And btw, can anyone in this forum, or only the whole world, say they totally understand waves? Meaning they can differentiate between the idea of it being a particle and a wave (and explain why it is either one and not the other), its size, the effect of it's amplitude and also relate it all together. They would also have to be able to explain any quantum mechanics to do with it. Anyone?

(if anyone actually does think they can answer them, I'm still in highschool :wink:, I'd like to ask them a few questions so give me a PM)
Reply 17
monagro
I totally agree. And btw, can anyone in this forum, or only the whole world, say they totally understand waves? Meaning they can differentiate between the idea of it being a particle and a wave (and explain why it is either one and not the other), its size, the effect of it's amplitude and also relate it all together. They would also have to be able to explain any quantum mechanics to do with it. Anyone?

(if anyone actually does think they can answer them, I'm still in highschool :wink:, I'd like to ask them a few questions so give me a PM)


Ok the fact that light is described as both a wave and a particle is somewhat confusing to most people, because they tend to imagine the two as fundamentally different.

Try to think of light having properties that are both wave like and particle like at the same time, it's more correct to say they aren't both a wave and a particle at the same time but share the properties of both. No one is entirely sure what exactly light is exactly, they are as sure as they can be that it has no mass, but at the same time they are sure that it exerts a physical pressure and that it's spectra are quantised in discreet amounts of energy. It's also a good idea to consider light as discreet particles called photons as well, for certain purposes, such as their absorption into the electrons and emission.

Where as it's more useful to define them as waves when they are propogating. The problem with the wave like properties of light is that we know they travel as waves, and we know in a slit experiment they create interference patterns just as say a water wave does when the ripples meet. The troubling thing is that if you have a single photon travelling towards a slit the light appears to interfere with itself, as we proceed to fire single electrons through a slit, we get an interference pattern in the same way we would if we shone a beam of light throught the slit? What can we assume from this? Only that light is in a superposition of wavelengths and actually passes through both slits which causes it to interfere with itself.

Now that's a tad confusing but here's where it gets even more tricky, if you try to detect which slit the photon is passing it appears to go through either one or the other 50% of the time. And the act of measuring it destroys the interference pattern, the photons strike the back of the screen as if they were particles in a ratio of 1:1 or 50%, rather than interfering as they would as waves in superposition.

So we have a problem, measuring the wave decoheres it and makes it act like a particle, if that is the case how can we see what light is actually like? Since the act of measurement decoheres its superposition, how can we be sure what it is we think is a wave of potentially infinite superpositions? Is it actually anything like the maths we have created to posit the wave function?

By the way the Schrodinger Equation above is a two dimensional representation of the wave function. As yet no one has managed to convert it to three dimensions in either polar or cartesian co-ordinates. So it has x and t. This is due to the squaring of function which limits a particles position to probabilistic values of x at time t which gives the equation a more absolute value, if you square negatives they are positive and the same with positives, this removes the the wave and converts it into a probability distribution.

So how do we know what we are mapping is anything like light? Well there is one rather clever method using squibs which detect where the wave isn't, by doing this we can build up a sort of image of the where the wave is not; thus we know the maths is at least a good representation even if it isn't an exact model of what is happening, we know it is to all intents and purposes a very accurate representation, from this and various other experiments.

In short Light is neither a wave nor a particle it is both or exhibits properties of both, call it a warticle if you like.

Since a wave has no size other than a wavelength and no mass it is useless to describe light as having size, it is considered to all intents and purposes as a point like particle. If it does have a mass, which we think unlikely although possible then it's size is likely to be beyond our means of detecting anyway.
Sidhe
Ok the fact that light is described as both a wave and a particle is somewhat confusing to most people, because they tend to imagine the two as fundamentally different.

Try to think of light having properties that are both wave like and particle like at the same time, it's more correct to say they aren't both a wave and a particle at the same time but share the properties of both. No one is entirely sure what exactly light is exactly, they are as sure as they can be that it has no mass, but at the same time they are sure that it exerts a physical pressure and that it's spectra are quantised in discreet amounts of energy. It's also a good idea to consider light as discreet particles called photons as well, for certain purposes, such as their absorption into the electrons and emission.

Where as it's more useful to define them as waves when they are propogating. The problem with the wave like properties of light is that we know they travel as waves, and we know in a slit experiment they create interference patterns just as say a water wave does when the ripples meet. The troubling thing is that if you have a single photon travelling towards a slit the light appears to interfere with itself, as we proceed to fire single electrons through a slit, we get an interference pattern in the same way we would if we shone a beam of light throught the slit? What can we assume from this? Only that light is in a superposition of wavelengths and actually passes through both slits which causes it to interfere with itself.

Now that's a tad confusing but here's where it gets even more tricky, if you try to detect which slit the photon is passing it appears to go through either one or the other 50% of the time. And the act of measuring it destroys the interference pattern, the photons strike the back of the screen as if they were particles in a ratio of 1:1 or 50%, rather than interfering as they would as waves in superposition.

So we have a problem, measuring the wave decoheres it and makes it act like a particle, if that is the case how can we see what light is actually like? Since the act of measurement decoheres its superposition, how can we be sure what it is we think is a wave of potentially infinite superpositions? Is it actually anything like the maths we have created to posit the wave function?

By the way the Schrodinger Equation above is a two dimensional representation of the wave function. As yet no one has managed to convert it to three dimensions in either polar or cartesian co-ordinates. So it has x and t. This is due to the squaring of function which limits a particles position to probabilistic values of x at time t which gives the equation a more absolute value, if you square negatives they are positive and the same with positives, this removes the the wave and converts it into a probability distribution.

So how do we know what we are mapping is anything like light? Well there is one rather clever method using squibs which detect where the wave isn't, by doing this we can build up a sort of image of the where the wave is not; thus we know the maths is at least a good representation even if it isn't an exact model of what is happening, we know it is to all intents and purposes a very accurate representation, from this and various other experiments.

In short Light is neither a wave nor a particle it is both or exhibits properties of both, call it a warticle if you like.

Since a wave has no size other than a wavelength and no mass it is useless to describe light as having size, it is considered to all intents and purposes as a point like particle. If it does have a mass, which we think unlikely although possible then it's size is likely to be beyond our means of detecting anyway.

It must have mass, as it is attracted by black holes and has an impulse.

Anyways, you don't seem to totally understand the nature of waves either. You are able to describe them into all detail we know about, but that is not the same as understanding anything related to waves.
Reply 19
monagro
It must have mass, as it is attracted by black holes and has an impulse.

Anyways, you don't seem to totally understand the nature of waves either. You are able to describe them into all detail we know about, but that is not the same as understanding anything related to waves.


Er it would be attracted to black holes by the curvature in space time, but that has nothing to do with it having mass. As far as we know, it has no mass, it might have a very small mass, but that is hypothesis.

Since no one is absolutely sure of what light is. Saying it exhibits properties of a wave and particle is currently the best description we have? If you think that isn't apt then I'd be delighted to hear why? Nothing I have described there is any different from what you'll find in a text book. As to exactly what a wave is, we can only postulate using mathematical equations, and interference experiments, they are as close as we have to an accurate model of the wave functions of light due to the measurement problem. I can't really go into great depth there, if you are not at degree level then trying to explain it mathematically would simply confuse you. And to be frank I need to study it in depth myself. That said as a simple overview that is perfectly adequate for your level I think.