Work of theory of everithing.

[Zubeen]

OK its right that Einstein put all his efforts in developing the THEORY OF EVERYTHING , but that doesn't means he wasted his second half of his life in doing so ! because some day and someone will complete the theory.
Einstein can't be such a stupid to waste his time for nothing !
But the thing i want to ask is what did the theory meant to do ? they say it was to unify the ELECTRODYNAMICS and GRAVITATION , but what does this "unify" word means (i am not asking the literal meaning but the scientific meaning ).
Please explain !

 

[Studiot]

You have posted this in the forum "beyond the standard model".

I wonder first if you have met the standard model?

Personally I try to avoid grand unified theories of anything because they pretend to answer some question of the form

"What is...XXX..?"

an impossible question.

I prefer to note that theories present models which offer a way of understanding some part of XXX and even providing way of usefully calculating some property.

In regards to your specific question scientists have long been unhappy with the idea of "action at a distance"
Whereby some body can influence some other body without any tangible connection to it eg by gravity or magnetism or whatever.

It was in pursuit of solving this conundrum that Einstein was looking for a unified theory, especially since his earlier and first theory of relativity (SR) laid down a limit to the rate of propagation of such influence.

Today we have still not resolved this issue but have several theories on offer.

Scientists are also a inherently a lazy bunch so they like the process of generalisation where a theory (model - that word again) is modified to expand its scope. Better yet if that expansion can encompass another apparently unrelated model about something else so they only need one model instead of two.

go well

 

[bapowell]

OK its right that Einstein put all his efforts in developing the THEORY OF EVERYTHING , but that doesn't means he wasted his second half of his life in doing so ! because some day and someone will complete the theory.
Einstein can't be such a stupid to waste his time for nothing !
But the thing i want to ask is what did the theory meant to do ? they say it was to unify the ELECTRODYNAMICS and GRAVITATION , but what does this "unify" word means (i am not asking the literal meaning but the scientific meaning ).
Please explain !

What is meant by unification in this context is a single theoretical framework that is capable of describing both gravitation and electromagnetism. In particular, there should be a single field that mediates both the gravitational and electromagnetic forces, not two distinct fields. Unified field theories propose that seemingly distinct forces are ultimately different manifestations of the same fundamental force.

Einstein's work to unify gravitation and electrodynamics ultimately didn't pan out, but the idea of unification -- that it is possible to describe nature in terms of a few fundamental fields that give rise to a wide range of interactions -- is still alive and well. In particular, so-called Grand Unified Theories (GUTs) in particle physics attempt to describe the three fundamental forces -- electromagnetism, strong nuclear, and weak nuclear, as a single fundamental force. The idea is that, while distinct and separate forces today, early in the history of the universe when energy densities were much higher, these forces unified into a single interaction.

Note that Einstein wasn't the first to think in terms of unification. Maxwell was doing this very thing when he developed his formalism revealing that electricity and magnetism were really two manifestations of the same underlying interaction.

 

[bapowell]

Today we have still not resolved this issue but have several theories on offer.

We have not resolved the issue of action-at-a-distance? Why do you say this?

 

[Zubeen]

OK, now i have 2 questions -
a) before knowing all this, i thought that whatever it may be ( the theory of everything) it must be something very difficult. But now after you explained it to me, i am thinking that is this unification possible? actually we know exact precise formulas for gravity and electrodynamics and we are using it since decades as two other forces, so if there would have been some chances of unification , we would have got it ... at least some hint regarding their unification... do we have any hint or experimental result that gives rise to the possibilities of this unification ?

b) And i heard that it was quantum theory which made him to work on the theory of everything, because he wasn't satisfied with the ideas of the Quantum theory so to dismiss that theory he tried making theory of Everything. But how just the unification of Electrodynamics and Gravitation can account for the results of the experiments that gave rise to the quantum theory ? Quantum theory says that for exactly same experiments, there can be more than 1 results but how than any theory (even the theory of everything) will deal with this thing, theory always tends to tell the exact result of an experiment than why Einstein thought that this unification will enable him dismissing the Quantum theory ?
(I am a student of 12th standard from India so i have a very limited knowledge of quantum theory and all this and this even because of my interest in all this
)

 

[mitchell porter]

There are two other forces, weak and strong nuclear forces. Electromagnetic and weak forces are unified in "electroweak" theory. Then there are "grand unified theories" which combine electroweak with strong, and then if you "run the coupling constants" you go to the "GUT scale" which is getting close to the energy scale of gravity, so that is indirect evidence of total unification. Also we have lots of advanced theories which start unified and then at low energies break up into different forces. But so far none of those theories gets everything exactly right.

Quantum mechanics is a different issue. Einstein wanted a classical theory that unified gravity and electromagnetism, and then he wanted to get quantum behavior by special boundary conditions. But it didn't work and today people don't believe that can work, because of Bell's theorem. So quantum theory for most people is just the accepted framework within which all the theorizing occurs. But it's interesting that Gerard 't Hooft, who did so much to create the standard model of physics, is now trying to derive quantum mechanics from something deeper, just like Einstein.

 

[Zubeen]

Hey Mitchell porter ! thank you for this but what do you mean by "the coupling constant " and "energy scale of gravity "? does the energy scale of gravity means the particles having enough mass (and hence energy) so that gravitation can be applied on it ?
and what about the coupling constant ?

 

[Zubeen]

And as per my knowledge, all theories give precisely the result of all the experiment but quantum theory just gives the probability of what's going to happen , then how all other theories occur in quantum theory, and the knowledge i have about quantum theory i really think that there must be something wrong because i don't think everything is based on just probabilities and not the exact result.
Though i am too young and new to all this but i don't think that these are good reasons to stop me from thinking about these levels of theories !

 

[bapowell]

And as per my knowledge, all theories give precisely the result of all the experiment but quantum theory just gives the probability of what's going to happen , then how all other theories occur in quantum theory, and the knowledge i have about quantum theory i really think that there must be something wrong because i don't think everything is based on just probabilities and not the exact result.
Though i am too young and new to all this but i don't think that these are good reasons to stop me from thinking about these levels of theories !

Right, you do not yet have enough knowledge about quantum theory to hold such strong opinions. It might surprise you that QED (quantum electrodynamics) -- the quantum theory of light and matter -- is actually one of the most accurate scientific theories ever conceived. Using QED, the predicted electron magnetic moment is within ten parts in a billion of the measured value. As Feynman points out in "Surely you're joking, Mr. Feynman", that's like predicting the distance between NY and LA to within the width of a human hair!

 

[mitchell porter]

The coupling constant for a force is a number which says how strong the force is. But there are secondary effects which depend on how hard particles collide, so the effective strength of the force - including the secondary effects - changes with the energy of the collision. The "energy scale of gravity" is the very high level of energy at which gravity becomes strong enough to matter even in particle collisions, and what they found is that the strengths of all the different forces converge to a similar value at around that energy.

This was totally unplanned so it's nice evidence that unification of forces is real. But we haven't figured out the actual unified theory. We can start with the theory that has been tested (the standard model) or a slightly more advanced theory (grand unified theory) and take it up to high energies, and we get the unification. But what we really want is a theory which starts with one unified force, that splits up into the different forces at low energies, a bit like electromagnetism reveals itself as electric and magnetic forces. So people have been studying this in supergravity and string theory for over 30 years, and they have written many different equations, but so far we don't have a proof that any of them is the right one.

 

[Zubeen]

@ all
I want to thank PF because its the site , i have been searching for.
Its a very good platform for all Physics.
And to all subscribed to this thread - Please , if i'll ask some silly question, please help me clearing it because i really love physics and i want to learn a lot about it.
And i want to tell one more thing that the Discussion on this thread will go long ...

because i want to learn a lot !

 

[Studiot]

We have not resolved the issue of action-at-a-distance? Why do you say this?

We have merely hidden it behind some more words.

Wikipedia is not a bad summary in this case. At least it seems unbiased.

Zubeen you may be able to cope with this, and perhaps even spot the inconsistencies which are there because it is a work in progress, like the unification theories.

http://en.wikipedia.org/wiki/Action_at_a_distance_(physics )

 

[Zubeen]

The "energy scale of gravity" is the very high level of energy at which gravity becomes strong enough to matter even in particle collisions...

Gravitational force and energy have no relation unless we consider relativistic view of gravity, so are we considering relativistic view of it ?

And

... and what they found is that the strengths of all the different forces converge to a similar value at around that energy.

If we are considering relativistic view of gravity then at high energies there would be gravity plus the other force of interest than how can we say that the value of that particular force of interest have the value converging to the same value ??

 

[bapowell]

We have merely hidden it behind some more words.

Which words? I'm sorry, but I'm trying to get an idea of what your concern is.

Zubeen you may be able to cope with this, and perhaps even spot the inconsistencies which are there because it is a work in progress, like the unification theories.

Which inconsistencies? Are you referring to the non-locality of QM?

 

[mitchell porter]

Zubeen, I don't understand your second question. Why can't the strength of gravity and the strength of the other forces converge to the same value? No-one has seen it happen but it's mathematically possible. The standard model of the forces, which has been tested at low energies, already predicts approximate convergence at high energies. That is why people imagine a unified theory in which all the different forces are just components of one superforce.

Yes, I am assuming relativity, and also quantum mechanics. They are basic to everything in high-energy physics. You can speculate about a deeper foundation that's different, but it would have to make the world look relativistic and quantum at our energy scale.

 

[Chronos]

A deeper question worth exploring is why GR and QM don't play well together. Just itemizing the issues will make you wish you stuck to particle physics.

 

[Zubeen]

Well, can you please suggest me a book for all this.
The book should start from basics and reach out to the high level of the theory.
also please provide its link on the net .... please.

 

[MathematicalPhysicist]

I believe it should be theories

 

[bapowell]

Well, can you please suggest me a book for all this.
The book should start from basics and reach out to the high level of the theory.
also please provide its link on the net .... please.

That depends on your current level of knowledge. You need to start with a sound understanding of contemporary physics, including classical mechanics, electrodynamics, and quantum mechanics. It is unfortunately not possible to pick up a single book on grand unified theories without having gotten these other subjects under your belt. After these, you should study relativity (including some early universe cosmology), quantum field theory, and the Standard Model of particle physics. Gaining an understanding of the associated mathematics is also important; the big ones are: linear algebra, differential geometry, group theory, and eventually topology (Nakahara's book "Geometry, Topology, and Physics" is a good summary of the mathematics necessary to understand grand unified theories and string theory.)

If you seek a more popular-level introduction to modern physics, including cosmology, particle physics, and strings, the books by Hawking, Greene, Kaku, and Weinberg are mostly good.