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Which modern physics theories are worth knowing?

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rousseau

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One of my biggest weak-spots in science is physics. I understand all the basics: the laws of motion, the laws of thermodynamics, basically most of the stuff that you'd learn in high school or introductory university physics.

This brings me to what I'm calling 'modern physics', all of those really weird theories, that at face value seem extremely theoretical, which in probability may not even be true depictions of the universe. So when I ask 'which are worth knowing', what I mean is: 'which modern physics theories tell us something profound about the universe/reality and also have a high likelihood of being true?'.
 
rousseau said:
One of my biggest weak-spots in science is physics. I understand all the basics: the laws of motion, the laws of thermodynamics, basically most of the stuff that you'd learn in high school or introductory university physics.

This brings me to what I'm calling 'modern physics', all of those really weird theories, that at face value seem extremely theoretical, which in probability may not even be true depictions of the universe. So when I ask 'which are worth knowing', what I mean is: 'which modern physics theories tell us something profound about the universe/reality and also have a high likelihood of being true?'.
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The nature of science means that no physics theory (now, or in the foreseeable future) will be 'true' but each will be less wrong than its predecessor.

The big two to know are relativity and quantum mechanics. Each has had a profound impact on how we see the world and make startlingly accurate and counter-intuitive predictions.
 
beero1000 said:
The nature of science means that no physics theory (now, or in the foreseeable future) will be 'true' but each will be less wrong than its predecessor.

The big two to know are relativity and quantum mechanics. Each has had a profound impact on how we see the world and make startlingly accurate and counter-intuitive predictions.
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Can you explain what counter-intuitive prediction quantum mechanics makes (explained like I'm a 5 year old) ?
 
Extremely theoretical? Are you serious?

The Standard Model (which includes quantum physics) has the closest agreement between theory and experiment in all of science. Of course, that comes from quantum chromodynamics which also has the distinction of the worst possible agreement between theory and experiment (it predicted electrons would have infinite charge until Feynman and others whacked it with a crowbar and started duct-taping the pieces).

General relativity has also been tested really thoroughly.

The main problems right now are:

  • Every attempt at combining quantum theory with relativity (or heck, anything that includes gravity) results in equations that spew even more nonsense than quantum chromodynamics did before the crowbar application.
  • Relativity spits out a whole lot of nonsense when we try to describe black holes, namely a lot of crazy stuff happens at the event horizon and at the center of the black hole. Does reality really stop making sense at those places, or is there something really important missing from the equations?
  • What the fuck is dark matter?
  • What the fuck is dark energy?
  • What the fuck happened before the big bang?

Don't let any of that hold you back. It's worth your time learning what you can about relativity and quantum mechanics. I would actually suggest starting with YouTube for either of those things.

Just remember that when it comes to quantum physics, Feynman famously said that if you think you understand quantum physics, you don't understand quantum physics (heavily paraphrased), so a lot of it simply isn't going to make a lick of sense without the math, which is pretty intense. Remember your freshman physics class? Now imagine using probability functions in place of most of those scalar variables. Now imagine applying integrals and/or differentials to those bad boys. I'm sure you can imagine how messy the equations get, and the underlying concepts are so counterintuitive that the equations are about the only thing you can truly wrap your brain around.

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One book I would recommend is The Infinity Puzzle. It basically tells the story of theoretical physics from quantum theory to the Higgs field.
 
rousseau said:
Can you explain what counter-intuitive prediction quantum mechanics makes (explained like I'm a 5 year old) ?
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Heisenberg's Uncertainty Principle is a good one. It is impossible, even in theory, to know the location and momentum of a particle to arbitrary precision. No matter how smart you are, how carefully you construct your measuring equipment, how controlled you make your experiment, there is a fundamental non-zero lower bound on how much information you can get about a physical system. That is because everything, all the stuff around you that seems solid and tangible and permanent are actually just waves. Waves of matter that can interfere with each other, constructively and destructively, to appear and disappear and be in multiple places at once. Quantum mechanics predicts that there is a non-zero probability that a marble statue will wave its hand at you, or that you will teleport through a brick wall.

If that isn't the most ridiculous thing you've heard in your life, then remember that that was one of the tamest first predictions of quantum mechanics, and things have only gotten weirder since.
 
rousseau said:
Can you explain what counter-intuitive prediction quantum mechanics makes (explained like I'm a 5 year old) ?
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The one that is the most disturbing to me is the double slit experiment: .

Copenhagen interpretation: the electron passes through both slits, we find out which one when we measure it. The electron interferes with itself, unless we measure it before it passes through the slits.

Many worlds interpretation: there are two different universes: one in which the electron passes through slit A, and another where the electron passes through slit B. We find out which universe we're in when we measure the electron. The electrons in the different universes interfere with each other, but not if we take a measurement at the slits or before.

The infamous Schrodinger's cat is a thought experiment that is meant to make fun of the Copenhagen interpretation. Obviously, Schrodinger was more of a dog person.
 
rousseau said:
One of my biggest weak-spots in science is physics. I understand all the basics: the laws of motion, the laws of thermodynamics, basically most of the stuff that you'd learn in high school or introductory university physics.

This brings me to what I'm calling 'modern physics', all of those really weird theories, that at face value seem extremely theoretical, which in probability may not even be true depictions of the universe. So when I ask 'which are worth knowing', what I mean is: 'which modern physics theories tell us something profound about the universe/reality and also have a high likelihood of being true?'.
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John Bell's inequality theory
The apparent recent death of supersymmetry
Alan Guth's inflationary cosmology
Virtual particles pop in and out of existence in vast numbers thanks to the underlying unstable energy fields.
Field theory.
 
Read Feynman's excellent QED: The Strange Theory of Light and Matter (http://www.amazon.com/QED-Strange-Princeton-Science-Library/dp/0691125759)

He gives a terrific insight into Quantum Physics, aimed at the educated layman, with a minimum of complex mathematics.

I would also recommend to anyone interested in Physics his 1964 Introductory lectures; (The original films are now available online here: http://io9.com/watch-a-series-of-seven-brilliant-lectures-by-richard-f-5894600) although from your OP I would guess that most of this stuff is already known to you, it is a superb refresher, set out in terms so simple even Cornell freshmen could understand them. :)
 
Interestingly, I spend a lot of time in two areas that are toed to aspects of modern physics that are real life applications of quantum theory:

-Solid state physics in my case the development of materials, structures and devices to detect electromagnetic emissions.

- Emission and absorption processes from hard bodies and gases.
 
If you want an overview of how QM is applied without going too deep Streetman's Solid State Electrnic Devices.

An old used first edition works.

http://www.amazon.com/dp/013149726X...e=asn&creative=395097&creativeASIN=013149726X

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dockeen said:
Interestingly, I spend a lot of time in two areas that are toed to aspects of modern physics that are real life applications of quantum theory:

-Solid state physics in my case the development of materials, structures and devices to detect electromagnetic emissions.

- Emission and absorption processes from hard bodies and gases.
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Photon energy and band gap voltages? I was not a device physics guy but I was around IR detectors. MCT, PbSe, PbS
 
rousseau said:
Can you explain what counter-intuitive prediction quantum mechanics makes (explained like I'm a 5 year old) ?
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The most basic one I know of is interference. If you have an electron gun shooting electrons toward an electron detector through a barrier with a little hole in it, you'll detect electrons at a certain rate. If you make the hole bigger, of course the rate of detection goes up, just as you'd expect. But if instead of making the hole bigger you drill a second little hole next to the first one, the rate of detection might go up, or remain unchanged, or even go down, depending on exactly where you put the second hole. It's as though adding another lane to a highway causes more traffic congestion.
 
steve_bnk said:
If you want an overview of how QM is applied without going too deep Streetman's Solid State Electrnic Devices.

An old used first edition works.

http://www.amazon.com/dp/013149726X...e=asn&creative=395097&creativeASIN=013149726X

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Photon energy and band gap voltages? I was not a device physics guy but I was around IR detectors. MCT, PbSe, PbS
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I think we compared notes a long time ago. In my first job out of graduate school, I worked for a dinky little company doing work with HgCdTe, from lattice matched substrate material growth (CdMnTe and CdZnTe) to liquid and vapor phase epitaxy of HgCdTe.

These days I do more simulation work, hardbodies, plumes, environments, and don't get to blow things up nearly as much, at least, by accident.
 
Underseer said:
Just remember that when it comes to quantum physics, Feynman famously said that if you think you understand quantum physics, you don't understand quantum physics (heavily paraphrased), so a lot of it simply isn't going to make a lick of sense without the math, which is pretty intense.
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I always found that assertion a bit annoying. The Copenhagen Interpretation is pretty non-sensical, but most of the supposed 'wierdness' makes fairly intuitive sense under a many-worlds or information+entanglement model. The "collapsing wavefunction" thing in particular if far more sensibly viewed as measurment just entangling the observer and the observed.
 
For the last three months I have been re-reading Penrose's Road to Reality. (1994)

Penrose's interpretation about the U and R processes. U is Schroedinger's unitary evolution while R is the reduction (collapse). The Copenhagen R involves "observation." ("Observation" is measurement of what happened. Environmental quantum entanglement.)

Penrose proposes an OR: objective reduction. A self-collapse of the wave function. This, in turn, has lead to a theory of quantum consciousness. http://www.quantumconsciousness.org/penrose-hameroff/orchor.html

That is literally mind-blowing.

In other news they've done the two-slit experiment with C70 fullerene (buckyballs). A huge number of protons, neutrons and electrons in one wave. How big does it have to be to behave classically? Somewhere between C70 and lead shot.
 
Shall we suppose that Penrose is right and it takes quantum computing to be conscious?

I wonder if a robot with a quantum computer for a brain would be conscious in the same way we are?

What would be our ethical position regarding our creations?

That is some physics worth knowing.
 
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