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It's common to hear that physicists are trying to find a Theory of everything (TOE). We "logically" consider the more elegant / concise theory as true ... because beauty is thruth ... or is it ? What are the philosophical/empirical considerations that push many scientists to look for a TOE ? Is there any resonable reason (other than aesthetic) to look for a TOE rather that trying to explain different things with different theories ?

Thanks :)

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    Sabine Hossenfelder might agree with you. Here is her recent blog post about truth and beauty in science if you aren't familiar with her already: backreaction.blogspot.com/2018/01/… – Frank Hubeny Jan 4 '18 at 2:29
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    The obvious reason is that unified theories are easier to teach and apply, so they are always the first choice, other things being equal. However, other things may not be equal with increasing complexity price for unification, and physicists are not unanimous on the utility of TOE, many advocate against it. See Cao's Conceptual Foundations and the Philosophical Aspects of Renormalization Theory for their case against TOE. – Conifold Jan 4 '18 at 5:23
  • If it all came from a single "point" in "space" it all has to fit together. If it doesn't draw a complete and consistent large picture, then it likely wrong. And not just in the context of physics. – dtech Apr 27 '18 at 20:17
  • A theory of everything, in the conventional understanding of everything, is a huge and probably impossible order; TOEs in physics are actually domain specific, they relate to questions of fundamental physics and nothing outside of that. – Mozibur Ullah Apr 27 '18 at 20:42
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We need a TOE if we are ever going to make sense of the world. All phenomena are connected and so if our theory is non-reductive or partial it does not fully deal with even one phenomenon.

--"What are the philosophical/empirical considerations that push many scientists to look for a TOE?"

Scientists do not look for a TOE, or not as part of the day job. For a general theory we have to take a higher viewpoint and study metaphysics. What scientists call a TOE is usually a completed Standard Model or somesuch, thus a theory of hardly anything at all. A TOE must explain metaphysics and solve all of its problems.

Of course, there is no reason why a scientist should not search for a TOE, but they'd have to stand back from the test tubes and start wondering about the origins and nature of the laws of physics, consciousness, ethics, space-time and so on. If we confine ourselves to the natural sciences we cannot have a TOE.

--"Is there any reasonable reason (other than aesthetic) to look for a TOE rather that trying to explain different things with different theories ?"

Yes! We cannot understand the world if all we have is piecemeal theories. All metaphysical questions are immediately connected such that we cannot pick one out and have an isolated theory to cover it. It's all or nothing. This no less true for scientists than it is for anyone else.

For a philosopher the situation is even more stark. If we do not have a theory of everything then we do not have a theory of anything at all, just isolated conjectures.

Scientists do not search for a TOE, (albeit they do use this word). They search for theories limited to their domain. meanwhile philosophers must search for a TOE or go home. The idea we can have a theory of, say, space-time, freewill or ethics while having no general theory is a serious error of thinking and recipe for an endless muddle of mutually inconsistent partial theories - as we see from the academic literature.

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As other responses have pointed out, it's important to distinguish between a Theory of Everything (TOE) and a Grand Unified Theory (GUT). GUT is a much more specific theory, which would unify the 4 known forces into a single framework, effectively merging the Standard Model of particle physics with Einstein's theory of gravity.

A GUT would be a theory concerned with particles (or something smaller). While it is certainly true that all matter is composed of particles, it is unlikely that a GUT would be a TOE. A GUT would provide no explanation for the organization we see today in biology, for example. You would not be able to derive the dynamics of evolution by natural selection directly from a GUT, just as you cannot derive them directly from the Standard Model.

  • We "logically" consider the more elegant / concise theory as true ... because beauty is thruth ... or is it ?

This depends on what you mean by beauty. Typically scientists apply Occam's Razor, given two equivalent theories, the simpler one is prefered. This doesn't necessarily mean a simpler theory is more true, just that it is easier to work with.

  • What are the philosophical/empirical considerations that push many scientists to look for a TOE ?

Here I assume you are referring to a GUT not a TOE. Historically many theories in physics have been unified with other theories, providing a more general single theory where there used to be two or more. The first unification happened thanks to Maxwell, who showed that the phenomena of electricity and magnetism were intimately related. His equations unified not only the theories of electricity and magnetism, but also optics. See for reference: https://en.wikipedia.org/wiki/A_Dynamical_Theory_of_the_Electromagnetic_Field

The history of 20th century physics is in large part the history of unification. Electromagnetism was later unified with the nuclear weak force, known as electro-weak forces, which were later unified with strong nuclear forces. So historically, physical theories have been unified into more general theories.

Besides historical reasons, physicists have little evidence to suggest that the Standard Model will be effectively combined with gravity. Some authors (Marcelo Gleiser and Paul Davies among other), have pointed out that the search for a GUT may be due to the historical influence of Western Monotheistic thought on contemporary science. See for reference: Theories of Everything as a hold over from monotheism?

  • Is there any resonable reason (other than aesthetic) to look for a TOE rather that trying to explain different things with different theories?

If you mean a GUT, then the answer is yes. If you mean a TOE then No. A GUT would enable cosmologists to better explain the earliest moments of the universe, as well as the properties of black holes (or other massive tiny objects). Those are reasonable scientific goals.

A TOE on the other hand may be logically impossible. Godel's incompleteness theorems prove that certain types of logical systems (which could be something simple like arithmetic for example), will always have undecidable statements contained within them. Undecidable statements are logical statements which can not be proved to be true or false (consider the statement "This statement is false"). Godel Theorems demonstrate that in general a theory can be either complete (such that every statement in that theory is provable from its axioms or principle), or consistent (such that every statement in theory is decidable) but it cannot be both. This implies that a TOE, which would be a complete description of nature, would not be consistent, in that there would be some things which could not be proved to be true or untrue, meaning the theory would not be a theory of everything.

  • Good point about Godel. I believe there is an exception to the Godel rule which makes a TOE possible, but the issues are complex and I'm not certain. Opinions on incompleteness seem to vary a lot even among mathematicians. Hawking argued from Godel that physics must be forever incomplete but metaphysics is another matter. I may ask a question on this issue. – PeterJ Apr 24 '18 at 13:46
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When physicists talk about a Grand Unified Theory (GUT), which is often described as a 'theory of everything' in non-scientific circles, is a theory in which the 5 fundamental forces (strong nuclear, weak nuclear, electrical, magnetism, and gravity) are integrated into a single force. This is not sought after for pure aesthetics; and the Maxwell equations prove that.

James Maxwell (in 1861) first published the idea that Electrical force and Magnetic force could be integrated into an Electro-Magnetic force. This was the first integration of any of these forces. This integration led to a massive surge in capability of humans, has been primarily responsible for our development of technology during the 20th century and made things possible that we couldn't conceive of before this.

Radio. Radar. Steady power generation and transmission over power lines. Eventually valves. Transistors. Integrated Circuits (silicon chips). Computers. The phone. All of this was made possible with the simple idea that magnetism and electricity were related.

Why? Because we already knew how to make things spin. If we can do that, we know how to make electricity; you just spin wire in a magnetic field. Additionally, you could MAKE things spin by putting electricity through a wire inside a magnet.

What's the single biggest impediment to space exploration right now? The fuel cost. The Rocket Equation tells us that we have to carry with us a massive amount of fuel to escape the Earth's gravity, and that we have to carry more fuel to lift that fuel, then more fuel to lift that fuel, etc. What if defying gravity was as simple as getting an axle to spin in a specific way through a magnetic field? If there's a simple and cheap way to cheat gravity (or at least manipulate it, then space exploration would be safer and cheaper than our current chemical reaction rocket technology.

Just like EM theory changed our lives incredibly, we hold out high hopes that the same will be true as we integrate other forces. This may ultimately not be possible; they may come from different 'sources' so to speak. But right now, the potential gain makes the search worthwhile. Either way, we learn something new about how the universe works. Something that we may yet exploit to make our lives better.

That makes the search more than the search for elegance.

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From a more abstract point of view, we would like to have a full body of science that human beings could comprehend. But no one can comprehend an inherent contradiction.

If all the existing domain-specific theories never contradicted one another, we would have a unified theory, even if it were not elegant. There are situations we can imagine about which each separate domain-specific theory has something to say, where every force is relevant to an equal degree. And every such situation is a potential place where two domain-specific sciences will offer different answers.

We don't have some magical tie-breaking apparatus to decide which theory wins. So those situations remain something we cannot explain. And the ultimate goal of science as a whole is to explain as much as possible. So getting rid of those unexplained areas is obviously on the agenda.

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The purpose of a theory is to explain "why things happen" and be able to predict "what will happen". There are currently questions in physics about how the currently identified fundamental forces relate to each other, and the presumption is that resolving those questions in a Grand Unifying Theory would be more powerful in it's explanatory and predictive nature.

Do note that there is not, and will not be, a "theory of everything" which is one set of laws that explains all "things". The work in transcendental realism (Sayer, Bhaskar, et al) does a great job of explaining the need for identifying causal mechanisms as part of theories. For example, a foot pressing on a bicycle pedal "causes" a bicycle wheel to spin. These causal powers are stratified -- if you want to understand why pressing on a pedal causes a tire to spin, you have to understand gears and chains; to understand gears and chains, you must understand statics and dynamics; to understand statics and dynamics you must understand physics; and so on down.

The different causal mechanisms at different layers are non-reductive in their causal and explanatory powers. The chemicals Na and Cl are both poisonous to humans, however NaCl (table salt) is not. I wouldn't see a reasonable end game in trying to collapse all causal powers into a single traditional theory, but instead collecting and relating them together in some sort of ontology (of the computer science kind, not the philosophical kind).

  • Salt has an LD50 of about 2 tablespoons full. It is both essential for life, and poisonous – CriglCragl Apr 24 '18 at 18:37
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Theory Of Everything was first used satirically. Though, thinkers since at least the ancient Greeks have pointed to the possibility of and need for one. The known fundamental forces were for a long time thought to be simply seperate. But then electricity and magnetism were unified. Then in the search for unifying electromagnetism with gravity, the strong and weak forces were discovered. And the electroweak force, was found to unify electromagnetism and weak nuclear force at higher energies, making a model for expected unification of the other forces, at higher energies. In particular, the theories with the greatest explanatory power, general relativity and quantum field theory, can niether account for black holes where the energy levels and scale require information from both, which contradict each other.

So, historically, unifying fields has been a result rather than an expectation. Although, the scientific view presupposes substance monism; matter, energy, and to some extent space have been unified. We expect that in blackholes and the early fractions of a second after the big bang, that this unity of substance will be manifest and result in the patterns and behaviour we see. Expecting substance monism is really expecting explanatory unity

David Deutsch objects to a Unified Field Theory being treated as a Theory Of Everything. He suggests four domain-specific are essential for understanding everything, epistemology, computation theory, evolution, and the many worlds interpretation of quantum mechanics. Information certainly has fundamental consequences in physics, from entropy to event horizons. Deutsch argues that life is also fundamental, it's possibility and specific occurences, to understanding causal behaviour. And epistemology links minds to worlds.

Theories of Everything, generate diverse phenomena from simple axioms. Godel's Inompleteness Theorem deals a devastating blow to this model of explaining things, finding that the behaviour of an axiomatically derived system is not fully determined by it's axioms. This suggests that a Unified Field Theory would not be a Theory Of Everything. This line of reasoning convinced Hawking there would not be a TOE. However, reasonable objections can be made about explanatory power, vs decidability. This may allow emergent systems -like life- to not be fully accounted for by a UFT with explanatory power to account for all the fundamental physics. So, requiring domain-specific theories. This can also further be supported by the idea any theory has limits to accuracy, and theoretical models should not be confused with reality.

The idea that physics has fundamental explanatory power, presupposes hard reductionism - which we have good experiences with, but no deep evidence for. It has computability on it's side, but really nothing deeper.

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I found this quote attributed to theoretical physicist Wolfgang Pauli

“When one analyses the pre–conscious step to concepts, one always finds ideas which consist of ‘symbolic images.’ The first step to thinking is a painted vision of these inner pictures whose origin cannot be reduced only and firstly to the sensual perception but which are produced by an ‘instinct to imagining’ and which are re–produced by different individuals independently, i.e. collectively… But the archaic image is also the necessary predisposition and the source of a scientific attitude. To a total recognition belong also those images out of which have grown the rational concepts.”

As such an artist aspiring to provide you "predisposition":

A Quantum Frame Key

My non-scientific aesthetic theory of everything model visualizing the Electromagnetic force using a Golden Rectangle “A Quantum Frame Key” or: how I stopped worrying and quantized 0-3 dimensions of the electromagnetic force at Planck

Here the Electromagnetic force is shown in the color white and the 4 squares form a Planck area rectangle representing the effective frames of reference or dimensions 0-3 of the Electromagnetic force. These dimensions are shown as filled with tessellations between the Electromagnetic force and as it’s Schwarzchild radius/event horizon, shown in the contrasting color black

  • "the Electromagnetic force and it’s Schwarzchild radius" -_^ – CriglCragl Apr 24 '18 at 18:43
  • (I corrected my typo to include "as")... and I feel "radius" isn't correct term at this scale... I'm wondering if the color black is as the reduced Planck constant because de Broglie wavelength emergence is exhibited – Jeremy Popejoy Apr 27 '18 at 20:41

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