Theories Definition and 486 Threads

Can someone tell me a theory in which the lowest twist operators are not the stress tensor and its derivatives? My aim is to work out the lightcone OPE for the theory and derive bounds like the averaged null energy condition. (as worked out in https://arxiv.org/pdf/1610.05308.pdf)

In classical mechanics I would say: a particle can have any initial position and velocities, Newton laws give you the evolution of the particle: F=ma , is the basic equation, if you know the forces acting on the particle by solving this equation you get the future values for velocity and...

I am confident that there are scientific nut cases in every country (there certainly are in the US) but usually they are fringe people or just crackpots. It has long amazed me the extent to which seemingly responsible people in India subscribe to ridiculous theories. I've had a couple of direct...

It goes without saying that theoretical physics has over the years become overrun with countless distinct - yet sometimes curiously very similar - theories, in some cases even dozens of directly competing theories. Within the foundations things can get far worse once we start to run into...

Homework Statement The exercise needs us to first show that ##P^2## (with ##P_\mu=i\partial_\mu##) is not a Casimir invariant of the Conformal group. From this, it wants us to deduce that only massless theories could be conformally invariant. Homework Equations The Attempt at a Solution I...

Hello. I'm a bit out of my depth on this one, so please bear with a beginner (me) trying to figure this out. Here's a quote that's thrown me and I'd like some help in understanding and interpreting it. Thank you. "I am persuaded that a tensed theory (or so-called A-theory) of time is true...

Just a question: Can anybody give any information regarding the black hole paradox? There are so many theories behind it. Which one should we believe? Just a general question.

There is a an encyclopaedia of all the different inflationary models. But I am wondering is there is a similar list of modified gravity models ?

Hi, I'm new on here and this is my first post, so forgive me if I don't master the threads instantly :) - right, now that's out of way: I want to open a discussion on the singularity in Black Holes, namely in regards to the well known issue of Special Realitivity breaking down at the...

This thread is about the process of theory completion in the practice of theoretical physics, and therefore mostly directed towards practicing theoretical and mathematical physicists, but others can chime in as well. a) What exactly constitutes a natural completion of a physical theory? b) Is...

Moderator's note: This is a sub-thread spun off from https://www.physicsforums.com/threads/is-the-ground-state-energy-of-a-quantum-field-actually-zero.953766/. I should have said that in certain cases in QFT, we can neglect “surface terms”. For example, the (on-shell) difference between the...

Hi all, I’d like to ask why do we need to modify the General Relativity with theories like F(R) modified gravity ? Thanx

Can string theory be made without time equations? According to Carlo Rovelli in his latest book "The Order of Time" https://www.amazon.com/dp/073521610X/?tag=pfamazon01-20 : "The equations of loop quantum gravity on which I work are a modern version of the theory of Wheeler and DeWitt. There...

Why theories of failure have been developed from 1-D tensile testing. Why can't we go 2-D testing or 3-D testing?

I thought about something interesting. Essentially any scientific theory is just a subset of the powerset of all possible human thoughts. Good theories are just stories within that powerset that happen to have predictive power and hence are useful to us. But the powerset of all possible human...

Dear All I am interested in studying the ADM formalism for gravity theories. After finding the momentum and getting rid of the time derivative variables ,One of the steps is to write the hamiltonian as sum of 2 parts of coefficients the lapse and shift functions repectively H= N H_t + N_i H_i...

Every time I watch another YouTube video about the "spooky" stuff or multiple slit experiments they never have a proposed explanation of how they work. It would seem to me that if you had a proposed idea then people could think of experiments to prove or disprove the idea. But with no ideas it...

I'm trying to (re-)collect the physical theories that once were considered as a correct description of reality and worked to a certain degree, but were subsequently dismissed. I would say that the geocentric epicycle theory of Ptolemy could be considered an example. It correctly describes the...

Please let me know if this statement is correct, too vague, or blatantly wrong. I am doing research for an article I am writing, but am not a physicist, nor have I ever taken any physics instruction. If you have suggestions to fix it, please let me know! Thanks! Einstein thought the initial...

A not very well defined question: Path integrals (and generalizations) are sums over configurations. A logical extension of that process would be to sum not over configurations, but over theories (configurations are possible solutions of a single theory). Renormalization already plays around...

But someone does make new formulas and theories? Did all of them first learn about the existing knowlegde first? Like church made geocentric theory but copernicus made heliocentric using observations. Did he have to learn geocentric first? I am asking this because if the people are studying...

Is it possible that two physical theories are equivalent in the sense that their predictions are exactly the same but the mathematics they use is different?

I wonder why we have actually only two theories of gravity, only one "theory of the microscopical world". There are a lot of brilliant people working on physics. I would expect new theories (that work) appearing like every year... I would expect we having now dozens of theories of gravity, each...

how should incompatibile scientific theories be thought of? Newtonian mechanics and special relativity contradict each other for example, so it doesn’t make sense to just consider all scientific theories to be part of one big coherent picture. How do scientists think about scientific theories...

Hi there. I was wondering if there are classical theories for the weak and strong interactions. I am relatively new to physics so I do not know the answer. Also, is there any classical theory for the electroweak interaction? Thanks in advance.

I want to casually discuss possible scientific theories but it seems like all forums prohibit that type of discussion...

Why mathematicians do not solve mathematical theories in different fields, name quantum mechanics that tries to describe gravity or any other theory such as multiverse/lqg/branes etc. It's just pure mathematics, only this language can fully describe universe, so why is it still just a theory...

Hi all Decided to post in 'beyond standard model' because lattice gauge theories are usually used to explore these models. Hope that's all right. So in lattice simulations, phase transitions in beta mass plane seem to have an important meaning. I understand phase transitions from a...

So according to Dr. Frederic Schuller, we need to at least know the topology on the space of all theories in order to know that we are getting closer to the truth. I take that this is because we need to know the topology to establish that convergence is possible in the first place. How does this...

Im doing a group presentation in one of my astrophysics papers this semester, and my part of the presentation is to research and outline the various theories for what dark matter could be. Does anyone on the pf know of any sites they may think will be helpful in my research, or any ideas on...

Please give list of superceded theories in which the classical version is outdated and where the classical version is still required, for example: In going from Newtonian gravity to General Relativity, we can do away with Newtonian gravity and use only General Relativity... In the atom, we can...

in the event violation of lepton universality is measured and established at 5-sigma level what are some theories that extend the standard model that would explain violation of lepton universality, while consistent in other SM measurements? how would violation of lepton universality impact...

Simply stated the Quantum Theories are flawed, how can the Quantum particles or particles be misbehaving if they're not being observed, but when we observe them they start doing what they were intended to do? I believe the particles aren't misbehaving at all, the particles were all ways doing as...

Years ago after reading Ch. 12 of Peskin and Schroeder (and the analogous discussion in Zee), I thought I fully understood the modern Wilsonian view of renormalization, and how it explains why non-renormalizable field theories still have meaning/predictive power at energies well below the...

Suitable for a student who has a background in undergrad general relativity. Many thanks

As I understand Aristotle believed that gravity was caused by certain objects trying to find the centre of the universe which was of course at the centre of the Earth. Newton gave us a better theory of gravity, but there were heliocentric philosophers before Newton. Not just Copernicus , Galileo...

Classical physics is a nonlinear theory, but how is it that? Why is it nonlinear? Also quantum mechanics is a linear theory so that the sum of the solutions of the schrödinger equation is itself a solution. But I'm not sure I grasp this completely. Why is quantum mechanics linear while...

In QCD, there are quarks at high energies, and pions are composite degrees of freedom that appear at low energy where the quarks are strongly coupled. The pion Lagrangian is non-renormalizable; it breaks down at the QCD scale and must be replaced by the full UV-complete theory of QCD...

Dark Matter was never found, what Modified Gravity theories should we check now?

Hello, I am doing a physics exam, where I have chosen to create a Brachistochrone curve, and perform various tests on it. Furthermore, I also have to write a physics report, containing the theory behind the curve, but I am not 100% sure what some of the theories behind the curve are. I suppose...

I am looking for something to read about the history of solution theories. Is there a good article or book that you may recommend?

Quantum theory, although hard to understand with intuition has a lot of experimental proof. Do the more modern theories e.g. String theory, or black hole theories have any experimental proof, or are they theories that the mathematics have led to? Without proof, do they deserve so much credit...

Let me write a brief intoduction to my question, just to clarify what I am not asking here, since it has been already discussed elsewhere. [1] intro Well, it is well known how the classical world of our experience can emerge from quantum mechanics in terms of decoherence. But it doesn't seem...

I often read about how famous theoretical physicists have made ground-breaking contributions to physics, but I always end up wondering how they are able to "discover" something that they have never seen or experienced. I believe that it has to do with the application of mathematical theories to...

Are there any linear quantum gravity theories out there with respect to the wave function?

the current SM states that electrons, muons and tau are all different fundamental particles. are there any theories that suggest there is only 1 fundamental charged lepton, the electron, and that muons and tau are either electrons that are in a higher energy quantum state, and therefore mass...

Consider a quantum scalar field theory with interaction terms of the form ##\phi^{n}##, where ##n## is not an integer. Where are some examples of physical theories which involve such interaction terms?

I was researching variable speed of light theories as alternatives to inflation theory; from Wikipedia I cam across this: "The idea from Moffat and the team Albrecht–Magueijo is that light propagated as much as 60 orders of magnitude faster in the early universe, thus distant regions of the...

The universe is expanding at an accelerated rate. Space has no edge. If space is geometrically "round," meaning that a long enough journey could bring you back to where you started, then it could be said that the universe has no outer edge. At the moment of the big bang, the universe created...

Well, I'm planning to learn from this book when i finish Shankar's Principles of Quantum Mechanics, if it fulfills the requiriments in this part, but from where i can learn the Special Relativity necessary to tackle this book?