Questions tagged [unified-theories]

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57
votes
2answers
10k views

Why is gravity such a unique force?

My knowledge on this particular field of physics is very sketchy, but I frequently hear of a theoretical "graviton", the quantum of the gravitational field. So I guess most physicists' assumption is ...
34
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1answer
3k views

What does it mean to say that “the fundamental forces of nature were unified”?

It is said that immediately after the Big Bang, the fundamental forces of nature were unified. It is also said that later they decoupled, becoming separate forces. Indeed, if we look at the list of ...
32
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3answers
4k views

Can all fundamental forces be fictitious forces?

After reading many questions, like this and this, I wonder: Is it possible to consider the other fundamental forces too, the electroweak interaction and the strong interaction or ultimately the ...
32
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4answers
12k views

Why is gravity so hard to unify with the other 3 fundamental forces?

Electricity and magnetism was unified in the 19th century, and unification of electromagnetism with the weak force followed suit, bringing into play the electroweak force. I've been told that ...
28
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9answers
11k views

Why are extra dimensions necessary?

Some theories have more than 4 dimensions of spacetime. But we only observe 4 spacetime dimensions in the real world, cf. e.g. this Phys.SE post. Why are the theories (e.g. string theory) that ...
22
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6answers
3k views

Does Kaluza-Klein theory successfully unify GR and EM? Why can't it be extended to the Standard Model gauge group?

As a quick disclaimer, I thought this might be a better place to ask than Physics.SE. I already searched there with "kaluza" and "klein" keywords to find an answer, but without luck. As background, I'...
21
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2answers
3k views

The physics community's take on non-commutative geometry

Connes's non-commutative geometry program includes an approach to the Standard Model that employs a non-commutative extension of Riemannian metric. In recent years I've heard physicists say that this ...
19
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1answer
2k views

What is the justification for Dirac's large numbers hypothesis?

Dirac stated that "Any two of the very large dimensionless numbers occuring in Nature are connected by a simple mathematical relation, in which the coefficients are of the order of magnitude unity." ...
13
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2answers
579 views

How do we know we've unified two interactions?

What is the precise definition of unification of fields (in classical and quantum mechanics)? In general, does unification of a field mean that we can write both of them at both sides of an equation (...
12
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5answers
3k views

Why do we say there are four fundamental forces in the Standard Model (if gravity is included)? [duplicate]

In my physics textbook (and in popular science culture) it is stated that there are four fundamental forces: electromagnetism, strong, weak, and gravity. But Wikipedia tells me that there is a ...
10
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2answers
1k views

Are the fundamental forces unified in a black hole?

Regarding the question of unification of the forces it is usually presented the following diagram: So it seems the matter of whether the forces are unified or not relates to how high the energy is. ...
8
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1answer
607 views

How did Einstein plan to Unify Electromagnetism and Gravity?

I'm asking the question on this site because I'm more concerned with the physics and philosophy of unification than historical details I know that Einsteins description of gravity includes curvature ...
8
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3answers
722 views

Why to unify gravity with the other forces if gravity isn't really a force?

As I understand, the Theory of General Relativity says that the force of gravity doesn't exist. The planets move in elliptical orbits because the spacetime is curved by the mass of the sun, not ...
7
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1answer
2k views

Early time in the Big Bang

I am not a physicist, so I would really appreciate using a simple language for the explanation of my question. From what I understood at the early Big Bang the four fundamental forces were unified to ...
6
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2answers
831 views

Should 4 fundamental forces really be 3 because of electroweak unification?

I read @ http://www.particleadventure.org/ Physicists concluded that, in fact, the weak and electromagnetic forces have essentially equal strengths. This is because the strength of the interaction ...
6
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4answers
4k views

Why is there a need to unify quantum mechanics and general relativity and what is meant by such a unification?

If general relativity (GR) describes gravity as a fictitious force, then shouldn't it be easy to quantize gravity in the sense that the spacetime distortion of a body changes in discrete values as a ...
6
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3answers
1k views

Does string theory and preons exclude each other?

Does string theory contradict the theory of preons, especially the Harari-Shupe one?
6
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1answer
2k views

Spontaneous symmetry breaking in SU(5) GUT?

At the end of this video lecture about grand unified theories, Prof. Susskind explains that there should be some kind of an additional Higgs mechanism at work, to break the symmetry between the $SU(2)$...
6
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4answers
597 views

GUT that includes all 3 particle families into a large group?

Explaining SU(5) GUTs (using the first particle family as an example) in the last SUSY lecture 10, Lenny Susskind mentioned that there are at present no ideas how to combine simultaneously all 3 ...
5
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1answer
426 views

How does physics research work? [closed]

I am going to try and be as short and as concise as possible. I was thinking these last few days about how we're still trying to discover a unified Theory of Everything. The question is: how is this ...
5
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4answers
226 views

Does any unifying theory explain why nature is Chiral?

I'm currently studying particle physics and find the experimental fact that massless particles are always left-handed quite surprising.In fact, the need to add projectors in the lagrangian seems not ...
5
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1answer
500 views

Do all the forces become one?

Were the forces of nature combined in one unifying force at the time of the Big Bang? By which symmetry is this unification governed? Are there any evidence for such unification of forces? Has ever ...
5
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4answers
240 views

Reformulating QFT to exclude space-time basis

This is, I guess, a pretty loose or general question and so I hope it's ok to post in this forum. But I suppose this is what science is all about: asking and seeing what happens. It is just personal ...
5
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4answers
233 views

Is there a theory where there are (recursively) infinitely smaller particles?

So I read that electrons are just points, with no mass, and furthermore, protons look like they have some "size" but that's really 3 "point-like" quarks. We first thought atoms were the smallest ...
5
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1answer
668 views

Why does the Standard Model not unify $SU(3)$ and $SU(2)\times U(1)$?

I am struggling with the definition of a unification. I read this question and i am wondering why the standard model is not unifying strong and weak force according to the given definition of a ...
5
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4answers
2k views

What is / are the primary criticism(s) against Einstein-Cartan-Evans field theory?

What is / are the primary criticism(s) against Einstein-Cartan-Evans (ECE) field theory? On Wikipedia the references provided were: arXiv:physics/0607186, MR2372785 (2008j:83049b), MR2218579 (2007a:...
5
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2answers
258 views

What is it exactly that conflicts when trying to unify all 4 fundamental forces? [duplicate]

Everyone knows that there are 4 fundamental forces: Gravity Electromagnetic Weak Strong At school and university you're taught that no one has been able to unify these 4 fources. However, not a ...
5
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1answer
122 views

Why did physicists in the 1950s and 1960s suspect the weak and EM interactions were at some level the same interaction?

Around the 1950s and 1960s there was a lot of work in particle physics motivated by two issues - finding a workable quantum field model for the weak interaction, and finding a model that unified the ...
4
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4answers
2k views

How are theories in physics validated against existing knowledge in practice?

Often you hear people mention how most attempts at Unified Theories haven't "accounted for all the experimental observations". The question is, how do you know you have accounted for all of the ...
4
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3answers
647 views

Unification of gravity and electromagnetism

Have there been any attempts at unifying gravity and electromagnetism at least at classical level since Hermann Weyl's idea of gauge principle (1918)? We now have Standard Model which is very ...
4
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3answers
2k views

How does string theory try to Unite Quantum mechanics with General relativity?

I've always thought that the reason we had trouble unifying Quantum mechanics and General relativity is: Quantum mechanics is defined "on" space time and time doesn't vary because of energy. Time is ...
4
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2answers
201 views

Unification of the electroweak theory

Can the electroweak theory be described by the spontaneous symmetry breaking of $SU(3)$ to $SU(2)\times U(1)$?
4
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2answers
332 views

Does the existence of dualities imply a more fundamental structure?

I was wondering if the existence of some kind of duality in physics always implies the existence of some underlying more fundamental structure/concept? Let me give a few example from history: Wave-...
4
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1answer
187 views

Is there a path to go from GR, to Gravitational Waves, to Gravitational Particles (Gravitons), to Quantum Gravity?

The articles on the subject often say : a part of the mass of the 2 celestial bodies became energy for gravitational waves after merging : E(gravitational waves) = (M1 + M2 - M_merged).c^2 ...
4
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1answer
22k views

Unified field theory in layman's terms

I watched some videos on the unified field theory, specifically interviews with Michio Kaku and John Hagelin, and want to learn a bit more about it. I looked up the theory of everything, string theory ...
4
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2answers
51 views

Uncertainty of the past

If the future today can be described as a complex set of probabilistic wave functions which collapse to form our reality, is it possible that the past history of the universe could also be ...
4
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3answers
333 views

Is there a mathematical relationship here or am I looking for relations when there are none?

When I was taking classical mechanics, we dealt a lot with pendulums, and orbiting bodies problems. This lead me to think about the two situations depicted above. Left: Shows two balls of equal mass ...
4
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0answers
720 views

Heisenberg's Unified Field Theory

While searching in the Internet, I came to know about Werner Heisenberg's attempt to obtain an Unified Field Theory (see the book Introduction to Unified Field Theory of Elementary Particles). But ...
4
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1answer
776 views

Are there any good books about Grand Unified Theories?

I'm starting to get a little desperate, because I can't find any introductory treatments of Grand Unified Theories (GUT). So far the only books I found are Mohapatra Unification and Supersymmetry ...
3
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2answers
798 views

Can a theory of everything solve the oldest problem of turbulence? [closed]

Can a theory of everything solve the oldest problem of turbulence? Can we have unified theory of universe without solving the problem of turbulence?
3
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3answers
829 views

The Role of Gravity among the Fundamental Forces of Nature

If we look at the standard model, we have 4 fundamental forces which include Gravity, Electromagnetism, Nuclear weak force, Nuclear strong force. I would like to look at Gravity for a minute. ...
3
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2answers
553 views

Quantum mechanics + General relativity =?

I have learned (the basics) of how one can incorporate the principles of special relativity to quantum mechanics to obtain quantum field theory. Can the same be done with GR and QM to obtain a new ...
3
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1answer
102 views

What is the mechanism that causes forces to get unified at high energies?

There are a lot of questions and answers on this site about the unification of forces, and all of them univocally say that at high energy levels, all the forces get unified. But none of them answer my ...
3
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1answer
124 views

Is Gravity still considered to be part of the “Superforce” which existed at the instant of the “Big Bang”

My limited understanding of the Big Bang is that all the Fundemental Forces (Electromagnetic, Weak Nuclear, Strong Nuclear and Gravity) were originally part of a "Superforce." As the universe cooled ...
3
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3answers
308 views

Are standard QFT and general relativity contradictory?

My professors say it's only a matter of finding the right mathematical formalism to unite GR and QFT, and that new physics can only possibly be found on extremely high energies and small scales. they ...
2
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2answers
124 views

Can classical theories exhibit quantum-like effects?

For quite a while in the first half of the 20th century, many physicists tried to concoct some manner of unified theory to explain all known phenomenon, a lot of them using geometric theories (ie ...
2
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4answers
2k views

What is a good non-technical introduction to theories of everything?

I'm not a physicist but I'm interested in unified theories, and I do not know how to start learning about it. What would be a good book to read to start learning about this topic?
2
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2answers
336 views

What is the relation between extra dimensions and unification of theories?

One of the most used methods in unification of theories is the use of higher dimensions. How does it actually work? If these dimensions are extremely small curled up, how does it affect the universe. ...
2
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1answer
88 views

Can anyone explain to a novice physicist whether there is a gravitational-electromagnetic symmetry?

I am trying to understand how the four fundamental forces relate to one another and to a theory of everything. As I understand it the unified force that is thought to exist at very high energies gets ...
2
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1answer
177 views

Why did Kaluza need to invent a new theory to unify general relativity and electromagnetism?

Wikipedia (and many other sources) say that by extending the number of spacetime dimensions from four to five, Kaluza–Klein theory unifies general relativity and electromagnetism into a single theory. ...