Quantum physics.
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Nothing is scientific fact, especially so-called scientific facts! Science merely makes predictions on the outcome of an event, tests and records the result of the event and derives an overall conclusion. The entire catalog of scientific knowledge is just the recorded observations of scientific experiments and the conclusions of the observing scientist(s).
Think of it this way. What happens if I were to drop an empty glass onto a concrete floor? It would shatter right? Ok so how do we test this? Easy! We just drop a glass onto the floor and see what happens. The problem is that we can only predict what the outcome will be, we cannot actually say for certain what will happen until we test it, and all we are really doing is observing and recording the results for that particular test. We can't call it a scientific fact because not every glass dropped onto a floor will shatter and we simply don't know until we test it and record the outcome.
Confused? Good, me too
mavity is the warping of space and time by mass, the more massive the object the greater the warping and thus the greater the gravitational pull. Space and time aren't seperate, they are combined in a 4 dimensional 'fabric' called space-time, 3 dimensions of space and 1 of time. Picture a star moving along through space-time, the heavy mass of the star stretches and bends the 'fabric' of space-time in much the same way as a basketball warps a bedsheet stretched between two fixed points. That dip in the sheet represents the effect of mavity, thus making less massive objects 'fall' towards a more massive one.
To answer the OP's question, quantum physics is the science of the very small. Einstein's theory of General Relativity is a set of principles which accurately describes and explains the motion and behaviour of very large objects in relation to each other, so we're talking moons, planets, stars, solar systems and galaxies, objects where mavity has a major influence.
Quantum Physics attempts to describe and explain the motion and behaviour of very small particles in relation to each other, particles like gluons, mesons, neutrino's, photons etc. On these scales, mavity isn't the major force in play since sub-atomic and smaller particles don't warp space-time like stars and planets do, so General Relativity can't explain their behaviour. These particles behave very strangely, appearing and disappearing, changing direction at random, even being physically observed as being in two places at the same time. It's all a rather chaotic, unpredictable and unstable environment compared to the relatively simple world of General Relativity.
Trying to combine Quantum Physics with General Relativity to create a single, unified theory or set of rules which accurately describes BOTH the very large scale and vary small scale environments is the holy grail of astrophysics and cosmology so if you figure it out, I'd like 50% of the credit/proceeds
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I saw a talk by Paul Nurse a few weeks ago (won the Nobel for medicine a few years back and present of the royal society, so generally a clever bloke). He mentioned quantum physics, and said that his daughter is a particle physicist working at the LHC. Apparently when he said to her that he worried that he didn't understand quantum physics, she told him not to worry, none of the quantum physicists do either. That's why they have meeting, to try and persuade each other that they're not as ignorant as they feel...
There's a very good explanation the quantum version of Young Slits experiment and other quantum stuff in Richard Feynman's book "QED". It was compiled from a set of talks he did to a lay audience. He starts off from a very odd direction, but the way he explains quantum effects does make a lot of sense once he has finished. And Lord knows only a few people have ever understood it better.
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Or is it that we can't (easily) measure the warping on this scale?
Simplest explanation, for want of evidence of any other mechanism, for this is that they are manipulated by something operating outside the physical constraints of this dimension, but for some reason people go into "head in sand" mode when this is suggested.
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Don't worry about it! I've just done had a series of lectures about it in my 1st year of Chemistry. I've looked over the notes, read the textbook and answered tutorial questions.... and I feel not too dissimilar to you.
Basically its to explain things at the atomic scale as classical physics breaks down at the atomic level.
Watch some videos on youtube, some horizon type shows then maybe move onto A level/ US College level stuff. There are some really good lectures done by University Professors.
Then maybe move onto articles from places such as New Scientist. They are a little dense but they are written in mind for people without a thorough science background.
http://www.newscientist.com/search?doSearch=true&query=quantum
Basically its to explain things at the atomic scale as classical physics breaks down at the atomic level.
Watch some videos on youtube, some horizon type shows then maybe move onto A level/ US College level stuff. There are some really good lectures done by University Professors.
Then maybe move onto articles from places such as New Scientist. They are a little dense but they are written in mind for people without a thorough science background.
http://www.newscientist.com/search?doSearch=true&query=quantum
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Sucks!Amazon said:
"Hyperspace" by Michio Kaku and "The Universe In a Nutshell" by Stephen Hawking were both easier reads compared to others I've attempted, and could also be a decent starting point. But you really have to know how to flush your mind of everything your currently understand.
Something I was reading the other day which is quite mind blowing.
The Planck Length is so small that if a single atom was expanded to the size of the known universe, the Planck Length would only be the size of an average tree.
The Planck Length is so small that if a single atom was expanded to the size of the known universe, the Planck Length would only be the size of an average tree.
I'm just coming to the end of my PhD in Quantum Physics, I have been simulating atmospheric chemical reactions using a simplified version (DFT and TDDFT) of quantum theory (when you read simplified version understand it still requires hundreds of thousands of CPU hours to compute). The reason to use such a simplified methodology is because of the 'many-body problem' where too many variables rely upon other variables to make things possible to be solved (i.e. electronic wavefunctions rely upon other electronic wavefunctions).
Quantum physics in a nutshell is all about the wave particle duality and the ability for any object to exist in both as both a wave and particle. This means that even a london bus will have a wavelength (however this wavelength is so large as to be indistinguishable), and calculating this is a favourite assignment to be given to undergraduate physicists. This ability for things to exist as both is fundamental to our understanding of electrons, where they can exist as both, only collapsing into the 'classical' understanding when the wavefunction is observed or measured. In simulation terms the electronic wavefunction is the hardest part to observe, solved using a simple equation:
\hat{H}P = Pe
where H contains all the interactions between the electrons and atoms in the system.
As for the applications of Quantum Physics to the world around you, one of my contributions to the scientific community as a whole (which I was published in a fairly prestigious journal about), is showing that there could potentially be a secondary reaction process which could dissociate CFCs in the stratosphere leading to ozone depletion, which would be more energetically favourable. But as other people have said, quantum mechanics is actually very important in the development of new drugs (when you do Folding@home I believe they are simplified QM calculations), CPU's work use band gaps which occurs due to quantum mechanics, global warming is due to quantum mechanical oscillations of CO2 and water, and in fact the vibrations of water in the atmosphere stops you from obtaining severe cancer from the UV rays from the Sun.
But as everyone has said, Quantum Mechanics is such a hard concept to understand, and requires years of work to get to even a rudimentary knowledge. I personally have been studying it for eight years and yet still some things elude me!
Quantum physics in a nutshell is all about the wave particle duality and the ability for any object to exist in both as both a wave and particle. This means that even a london bus will have a wavelength (however this wavelength is so large as to be indistinguishable), and calculating this is a favourite assignment to be given to undergraduate physicists. This ability for things to exist as both is fundamental to our understanding of electrons, where they can exist as both, only collapsing into the 'classical' understanding when the wavefunction is observed or measured. In simulation terms the electronic wavefunction is the hardest part to observe, solved using a simple equation:
\hat{H}P = Pe
where H contains all the interactions between the electrons and atoms in the system.
As for the applications of Quantum Physics to the world around you, one of my contributions to the scientific community as a whole (which I was published in a fairly prestigious journal about), is showing that there could potentially be a secondary reaction process which could dissociate CFCs in the stratosphere leading to ozone depletion, which would be more energetically favourable. But as other people have said, quantum mechanics is actually very important in the development of new drugs (when you do Folding@home I believe they are simplified QM calculations), CPU's work use band gaps which occurs due to quantum mechanics, global warming is due to quantum mechanical oscillations of CO2 and water, and in fact the vibrations of water in the atmosphere stops you from obtaining severe cancer from the UV rays from the Sun.
But as everyone has said, Quantum Mechanics is such a hard concept to understand, and requires years of work to get to even a rudimentary knowledge. I personally have been studying it for eight years and yet still some things elude me!
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No, if you don't explicitly measure which slit the particle goes through you'll get interference.
No, it is because of the way quantum field theory breaks a field into quanta. The method which works for the EM, weak and strong forces doesn't work with mavity, due to the units of the coupling constant G. When you work out the quantum corrections to it you find it is infinite. As I said in a previous post infinities aren't unheard of in *** but there are different kinds. Some of them are 'renormalisable', where you can extract useful information from the manner in which a quantity goes infinite and in other cases they are 'non-renormalisable' and cannot be made sense of. mavity is the latter.
The notion of renormalisability is useful one though. When you throw quantum mechanics, Lorentz symmetry (special relativity) and renormalisation into a bag and hit it with sticks the three smallest non-trivial examples you can build happen to be precisely those seen in nature, U(1) = electromagnetism, SU(2) = electroweak and SU(3) = strong. The U(N) and SU(M) refer to Lie groups, a way of describing symmetries. GUT models attempt to explain this by linking them all together into a single group.
No, that isn't the 'simplest explanation'. Quantum field theory, with goes beyond quantum theory by allowing particles to be converted into energy and vice versa, is considerably simpler than extra dimensional quantum mechanics. Adding in extra dimensions complicates general relativity, which in turn affects cosmology. The notion of an extra dimension was first put forth in the 1920s by Kaluza and Klein because if you work out the Einstein field equations of GR for a 5 dimensional space where one of them is hidden you get the 4 dimensional field equations plus electromagnetism plus a scalar massless field. This field isn't seen in nature, so while its a simple way to get electromagnetism from GR it isn't true. String theory has extra dimensions and one of the major lines of research is how you go about keeping these extra dimensions stable, because their configurations alter all kinds of things, like the size of the cosmological constant through to the strength of electromagnetism.
People don't go 'head in the sand' with such a suggestion. You'll find that huge numbers of theoretical physicists have no problem at all entertaining the notion of extra dimensions, I personally did my thesis on them. But they, sorry, we also know the knock on effects of introducing such things into current models and its not just a matter of "You can't see it so its in another dimension". String theory is abound with such notions, like the Randal-Sundrum (spelling?) brane model, but they have problems which have to be addressed. Quantum field theory deals with particle production and destruction without introducing extra dimensions, though extra dimensions can be introduced if you want. You should be very careful about thinking you have some great explanation just because you can throw together 3 qualitative sentences which don't strike you as having problems. I can guarantee that theoretical physicists have thought of more bat-**** crazy ideas then you have and have explored them more thoroughly than you could. Dismissing something because it's been examined and found wanting isn't putting ones head in the sand.
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The part I kind of struggle with (I don't understand the math, barely understand the logic), what do you mean by hidden, why does it need to be hidden (is it just to mathematically satisfy some expected result?), how does said dimension get hidden?
Sorry if this sounds stupid!
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We see only 3 spatial directions so anything saying there's more dimensions to space-time has to hide them in some way. One approach is to have our particles and all particles we interact with easily to be 'stuck' to a 3 dimensional object in higher dimensional space. This is the Randal-Sundrum model I mentioned. I can go into this in more detail if you want.
Alternatively you configure the dimensions such that they are curled up very very small. The standard example of this is how a hosepipe will look like a line (1 dimensional) from a long way away but to an ant crawling on it it obviously have length and circumference, its 2 dimensional. That's what K&K did, they rolled up the extra dimension into a circle of radius billionths of billionths of a metre in size. This is what string theory does, only with 6 dimensions you can make all kinds of crazy shapes, the somewhat well known Calabi-Yau manifolds being standard examples. Even the LHC can only probe to lengths of about 10E-18 metres, a million trillionth of a metre, while the string scale is 10E-33 metres ish and the Planck scale is 10E-35 metres. As someone has already said, the Planck length is to the atom what a tree is to the universe and consider how small atoms are to begin with! To probe the Planck scale you'd need an LHC larger than the visible universe.
If we are made of strings then we are constantly moving in all 9 spatial directions, just as we do normally through 3 we can see easily, but looping around the 6 small ones doesn't get you anywhere and its beyond our ability to measure the changes.
I can hear the indignant cries from the Intertubes of "So if it's so hard, if not impossible, to probe these lengths how can we ever demonstrate string theory valid?", which is a good question. Well we excluded the K&K approach in the 20s because they said we should see a kind of massless scalar field, which we could measure if it existed using current technology. The size and structure of extra dimensions in string theory alter the masses and properties of things we can measure. For instance, all coupling constants in string theory are actually determined by the structure of space-time and strings. The layout of the extra dimensions defines the amount of supersymmetry possible. This is why Calabi-Yaus are of interest, they lead to the only possible viable form of supersymmetry (N=1) while simultaneously satisfy the Einstein field equations. Thus you have the basis for a quantum field theory consistent with mavity, the only known example at present. Work has been done to work out what these sorts of effects would look like in a particle accelerator so that when LHC data is obtained we have a long check list of signatures and particle types, just as we do with the Higgs boson. If we see particular things then it would add considerable weight to string theory. An almost undeniable signature of extra dimensions would be the first few levels in a Kaluza-Klein mass tower, but we need much more powerful accelerators in order to see the first two states, even if the LHC could see one of them (else how do you know it's a tower of states if you don't see the second step?).
It's all quite interesting but unfortunately you rapidly get into the realm of quite abstract mathematics, much of which is less than 10 or 20 years old. Some of the spaces considered by string theorists could even be defined until this century, much less examined!
Alternatively you configure the dimensions such that they are curled up very very small. The standard example of this is how a hosepipe will look like a line (1 dimensional) from a long way away but to an ant crawling on it it obviously have length and circumference, its 2 dimensional. That's what K&K did, they rolled up the extra dimension into a circle of radius billionths of billionths of a metre in size. This is what string theory does, only with 6 dimensions you can make all kinds of crazy shapes, the somewhat well known Calabi-Yau manifolds being standard examples. Even the LHC can only probe to lengths of about 10E-18 metres, a million trillionth of a metre, while the string scale is 10E-33 metres ish and the Planck scale is 10E-35 metres. As someone has already said, the Planck length is to the atom what a tree is to the universe and consider how small atoms are to begin with! To probe the Planck scale you'd need an LHC larger than the visible universe.
If we are made of strings then we are constantly moving in all 9 spatial directions, just as we do normally through 3 we can see easily, but looping around the 6 small ones doesn't get you anywhere and its beyond our ability to measure the changes.
I can hear the indignant cries from the Intertubes of "So if it's so hard, if not impossible, to probe these lengths how can we ever demonstrate string theory valid?", which is a good question. Well we excluded the K&K approach in the 20s because they said we should see a kind of massless scalar field, which we could measure if it existed using current technology. The size and structure of extra dimensions in string theory alter the masses and properties of things we can measure. For instance, all coupling constants in string theory are actually determined by the structure of space-time and strings. The layout of the extra dimensions defines the amount of supersymmetry possible. This is why Calabi-Yaus are of interest, they lead to the only possible viable form of supersymmetry (N=1) while simultaneously satisfy the Einstein field equations. Thus you have the basis for a quantum field theory consistent with mavity, the only known example at present. Work has been done to work out what these sorts of effects would look like in a particle accelerator so that when LHC data is obtained we have a long check list of signatures and particle types, just as we do with the Higgs boson. If we see particular things then it would add considerable weight to string theory. An almost undeniable signature of extra dimensions would be the first few levels in a Kaluza-Klein mass tower, but we need much more powerful accelerators in order to see the first two states, even if the LHC could see one of them (else how do you know it's a tower of states if you don't see the second step?).
It's all quite interesting but unfortunately you rapidly get into the realm of quite abstract mathematics, much of which is less than 10 or 20 years old. Some of the spaces considered by string theorists could even be defined until this century, much less examined!
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Reading up on Randall-Sundrum, i was half expecting the 5d-4d equivalent of an orthographic projection from 3d to 2d, good lord there a lot to read up on.
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R-S models play an important role in understanding the mavity/gauge duality hypothesis in string theory. If string theory were killed tomorrow the mavity/gauge duality would live on, because its something which doesn't depend on its original string theoretic construction. It links classical 'normal' weak mavity, which we understand a great deal of, to strongly coupled gauge theory, which we don't understand as much of. In string theory this means you can explore 4 dimensional strongly coupled gauge theories which look a lot like QCD using 10 dimensional general relativity. Now that might sound like the choice between a rock and a hard place but the mavity model is a damn sight easier to work with. Plus it also, as the Wiki page on R-S says, links to technicolour, which is the alternative to the Higgs mechanism so if the LHC doesn't find the Higgs technicolour will play a much bigger role in quantum field theory than it currently does.
The R-S stuff does away with the issue of "Why are 6 dimensions curled up and how do they stay stable?", which compactification models have but by throwing out some of the symmetries the compactifications work on you introduce a lot of variety in your models, plus you're often still left with questions of how to stabilise certain parameters in a valid way, ie keep the branes apart by the right distance.
The R-S stuff does away with the issue of "Why are 6 dimensions curled up and how do they stay stable?", which compactification models have but by throwing out some of the symmetries the compactifications work on you introduce a lot of variety in your models, plus you're often still left with questions of how to stabilise certain parameters in a valid way, ie keep the branes apart by the right distance.
Yes but we still don't know (For sure) what mechanism on the quantum scale drives the gravitational force. Is it the graviton? If it is how does it work? Does it fling about through space time at beyond light speed like a boomerang? We haven't figure it out yet.
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General relativity says the speed of mavity is equal to the speed of light. It's difficult to measure with pin point accuracy the speed of mavity due to its weakness but in strong fields like orbiting neutron stars it has been measured to be the speed of light with a 10% margin of error.
This implies that if the graviton exists then it is massless, else it couldn't move at light speed. The guy who now holds the mathematics chair at Cambridge Hawking used to have was central to the initial development of string theory and his reason for thinking it's a worthy line of approach is that you only put in special relativity to string theory yet you're unavoidable led to the requirement your model has a massless spin 2 particle whose equations of motion are precisely the Einstein field equations, ie the graviton. String theory not only is consistent with quantised mavity, it demands it, and the behaviour it demands is precisely that which we observe mavity to have. This is one of the reasons string theory is falsifiable. If it'd predicted different equations of motion for this particle it'd be wrong, unavoidably so.
I remember my a-level physics teacher talking about this some years ago. Am i right in thinking if you could control your own wavelength in real-time you could walk through walls?
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If you could alter the value of Planck's constant for the particles in your body then you could. The constant basically measures how 'quantum' something is, so if you set it to zero then you recover classical mechanics results and its very very small value is the reason we don't see quantum effects on everyday scales. If you could dial it up to a large number just as you're about to hit the wall then you'd massively increase your chance of tunnelling through the wall and appearing on the other side.
Unfortunately your atoms and molecules would fall apart since their cohesion and structure depend on the constant too so you'd tunnel through and become a mass of lone electrons and quarks.
w00t, 100'th post was about quantum mechanics! That's why I've been keeping a close eye on the thread. Now I can go watch Battle Royale in peace!
But also I believe if you run at the wall enough times eventually all your atoms would tunnel through the barrier(s) (because in actual fact there are a lot of atoms in a wall!). Which is the same kind of thinking behind the whole if you put an infinite number of monkeys in front of typewriters you will eventually get Shakespeare!