Professor Hawking and The Unified Field Theory

I find it interesting that we knwo so much about physics and chemistry,but that no one knows why protons repel protons and protons attract electrons, ect. Basically what i understand the unified field theory to be is an explanation of why the 4 forces in the universe work the way they do. The four forces being - Gravity, elctrical force, strong nuclear foce, and weak nuclear force. Although I probably got the names of those last two wrong. So anyways my teacher told us that Einstein was tryign to figuret his out before he died and Steven Hawking is working of figuring ito ut now. Has he discovered anything? What do people currently believe causes this stuff?

actually, the search for a unified theory is an effort to reconcile relativity with quantum mechanics.
It’s also a search for a unified equation from which the 4 forces can be derived. It’s known already that the electromagnetic force and the weak nuclear force are described by a single set of equations at high energies. It is hoped that there will be a unified set of equations to describe all the forces.

Finding a quantum theory of gravity is also important, since relativity and quantum theory are both among the most successful theories ever advanced, but they don’t play nice together, theoretically.

Hmmm… Maybe I’m wrong (ok, probably I’m wrong:)) but I was under the impression that the Unified Field Theory was only intended to reconcile the Weak Nuclear, Strong Nuclear and Electromagnetic forces. To add in Gravity you need the “Theory of Everything” or TOE. Is this correct or do I need to check my dosages again?


You’re right… in that you’re wrong… In fact, inclusion of gravity was/is pretty much the point of it.

Einstein’s UFT was indeed intended to be a TOE.

I thought all the four forces except gravity have been unified.

Unified Field Theory is an attempt to combine all of the forces (strong and weak nuclear, elctromagnetic and gravity) together. Each force can be described by a field (a mathematical concept). James Clerk Maxwell did one for electromagnetism and Einstein did one for gravity. It is felt that at extremely high energies all forces unify into one force as opposed to four. Unofrtunately, for this to work, we need a quantum field theory (read very very small scales) fo each force. Electromagnetism has had its quantum field theory since the 1940’s (quantum electrodynamics). The other forces also have a quantum theory applied to them. In supersimple terms quantum theory describes the exchange of packets of energy that carry each force’s…uhhh…force (i.e. the electromagnetic force is carried by a photon).

All of the forces except for gravity that is. Gravity is stubbornly holding out so no unified field theory yet. No one has figured out how to successfuly describe the exchange of gravitons yet.

Detecting and/or measuring photons is easy and can be done in a high school physics lab. Detecting gravitons is another matter. Gravitons cannot be blocked by anything (there is no shielding from gravity while a piece of paper can shield you from a photon). Gravity is also by FAR the weakest of the four forces. You can feel the resistance of two refrigerator magnets being pulled apart yet you may hardly notice the weight of the same magnet. As regards the weight of the magnet you have to overcome the combined gravitational attraction of the planet earth to keep holding it.

A final feature of gravity that sets it apart from the other forces (I believe) is it is long range. The two magnets a few feet apart stop interacting but the same magnet will fell the pull of the earth miles up in the air. For comparison the strong nuclear force is VERY short range (it hold atoms together). I don’t know what the distance is on the weak nuclear force (responsible for some radiation) but I think it’s on the order of a few feet. What significance (if any) this may have I don’t know but it’s kind of interesting.

All four forces have already been unified…on paper, that is. It takes four dimensions to describe gravity…length, width, depth, and time. Mass distorts this space-time, and the distortion is gravity. Add a fifth dimension, and you get electromagnetism-electricity, magnetism, light, and chemical bonding. Add a sixth and seventh dimension, and you get the weak nuclear force…the process by which certain forms of radioactive decay arise. Eleven dimensions, and you get the strong nuclear force, which binds quarks together into protons and neutrons, and keep the atomic nucleus together.
There has been some progress in unification in practice…using atom smashers, they have unified electromagnetism with the weak nuclear force…the electro-weak force.
Top physicists extrapolate that the energy required to unify all four forces only existed at the birth of our universe… the big bang…way beyond our means.

I don’t think anyone has addressed the original poster’s question yet. Ryan is asking why do protons repel other protons and attract electrons. So far the answers are about what is meant by TOE.

But Ryan is looking for an explanation of what happens that a proton knows that another proton is near and should go towards it, or away from an electron. “Action at a distance” is not a very satisfying concept - we want to think in terms of things bumping into each other. Something that I can grasp by envisaging billiard balls.

Doesn’t the most accepted answer to this have to do with the exchange of virtual particles, in this case photons?

Anyway, I think this is what Ryan was asking, and that the part about the unified field theory was a digression. Sorry if I misstate your views, Ryan.

In hopes of addressing CurtC’s interpretation of the OP, here’s a quick summary of the ideas involved.

First, the experimentally supported theories:

  1. Gravity.
    Einstein’s theory of general relativity explains gravity. Particles travel along geodesics (shortest-distance paths) through spacetime. Spacetime is distorted by mass (energy), so the geodesics are not straight lines. General relativity (and special relativity) have rather straightforward postulates at their cores, but the above oversimplification belies the horror and beauty that these postulates produce in the math and in the predictions of the theory.

  2. Everything else.
    The other three forces are described by what are called gauge theories. This name just comes from the fact that all these theories have a certain symmetry to them. The long and the short of it – some smart people just tried various things until they started to work. Quantum electrodynamics (QED) was first. Its formalism was generalized to describe the weak interaction and then the strong interaction. While the interpretation of the math is really a matter of imagination, the essentially universal interpretation goes like this.

Quantum electrodynamics: Anything with an electric charge can interact with anything else with an electric charge by exchanging the QED force carrier – the photon. A photon acting as a force carrier is a photon only because it looks that way in the math. It’s not a real photon. (There are real photons, of course. You’re seeing some right now.) This virtual photon can carry over to the other particle whatever momentum it needs. And, in the case of particles that attract, the virtual photon “bumps” the two particles towards each other (now do that with billiard balls! :))

Strong interaction: Same thing, really. Quarks have electric charge, so they have to deal with all the QED stuff. In addition, though, they carry a different type of charge called “color”. Just like you say “positive” and “negative”, you can say “red”, “green”, or “blue.” These are just labels, of course. “Huey”, “Dewey”, and “Louis” are equally good labels for this charge. The math is a little uglier, by the same thing happens: two things with color can exchange the strong interaction’s force carrier – the gluon. (Gluons are massless and have color of their own, so they can interact with each other, making for some interesting physics. C.f., the photon. It has no charge, so two photons can’t interact with each other.)

Weak interaction: Same thing again. There’s really no name for the weak “charge”, but it hardly needs one since everything’s got it. Well, quarks and leptons do, that is. There are three different force carriers here – the W[sup]+[/sup], W[sup]-[/sup], and Z particles. These force carriers are not massless. In fact, they’re pretty heavy. This is why the weak force is so weak. It’s a big energy expense to make a heavy virtual particle.

I should say, I guess, what I mean by quarks and leptons. Everything is made up of quarks, leptons, and the force carriers (gauge bosons). There are six quarks (and the six corresponding antiquarks). These carry electric charge and color charge. There are 6+6=12 leptons/antileptons. Leptons carry no color charge and thusly do not feel the strong interaction. Half of the leptons are like electrons (including the electron itself), and half are neutrinos (light, chargeless particles). Since neutrinos carry no electric charge or color charge, they only feel the weak interaction.

The deeper question of “why” (e.g., why do like charges attract in QED?) really has no better answer than, “Because they do.” It’s actually not as bad as that, though. The inner workings of the math are really quite pleasing. That is, the ad hoc-ness goes mostly away. But in the end, even the prettiest math is only answering to the higher authority of experiment, and all experiment says is, “Because.”

To finish, do note that there are many theories that are still on the drawing board. People are working on gauge theories of gravity. String theory might explain particle interactions better. But all this is for another thread.


Personally, I would prefer to see that reworded from “explains gravity” to “describes gravity” or better yet, “describes the effects of gravity”. There’s a distinct and important difference. Just picking my daily nit…


I agree. I thought I did a thorough nit scan before I posted, but it looks like I missed (at least) one. :slight_smile:

One more nit: “Unified field theory” is a general term, which can describe any theory which unites multiple fields, such as Maxwell’s equations, which unify electricity and magnetism. The first unification of forces was probably Archimedes’ unification of the forces of gravity and levity (the tendancy of light substances (air and fire) to rise), but of course, folks didn’t think of them in terms of fields back then.

A Grand Unified Theory is usually taken to mean one that unifies the electromagnetic, strong, and weak forces, and if you toss gravity into the mix, it’s a Theory of Everything.