Theory Definition and 1000 Threads

Hello, I am studing theoretical physics and i would like to focus my work in string theory, but my fellows say that is a waste of time. ¿Do you think that is worthwhile to spend my time and effort un string theory? Greetings

My main question is regarding whether the membership relation is taken as an undefined concept (as is usually hinted in set theory books) or if the membership relation can be defined within the language of first order predicate theory. Let me describe a method to define the membership relation...

I want to discuss about two apparent contradictions that are on my mind for awhile. 1st: General Relativity predicts no radiation out of black holes. Quantum Mechanics does. If we perform an experiment and see that say, black holes radiates outwards, does that mean General Relativity is wrong...

I get a gist of how electric charge comes about in string theory here, https://physics.stackexchange.com/questions/5665/electric-charge-in-string-theory How much needs to be amended to the above answer to understand how color charge comes about in string theory? I assume there are interesting...

I'm studying Dynamo Theory, and have just a few questions. Today's theory says that currents in the molten outer core of the Earth give rise to magnetic fields. Now it would seem that the theory does not mean "molten iron currents", since together that is an electrically neutral substance, but...

Hi. Is there some kind of measure theory generalized to uncountable unions? Of course one needs to take care how to make sense of sums over an uncountable index set. I was thinking about following formulation of the additivity property of the "measure": $$\mu\left(\bigcup_{i\in\ I}...

I'm curious about something. And most of you are probably going to click away as soon as I say, or type this, I guess. But for those of who haven't, thanks. In the Iron Man comics, movies and tv shows the arc reactor keeps Tony Stark from lethal heart damage and keeps the Iron Man Armour...

What is the force acting on an object according to general theory of relativity? If there is a such a force, can we predict the motion of an object in general relativity just using the modified Newtons laws of mechanics i.e using relativistic mass of an object instead of rest mass ?

Hey there! I just want to ask if there are any books you would like to recommend that helps in studying high energy physics and HEP data analysis? Also can you recommend a good book for group theory and symmetry? I would be glad if you have links to free downloadable books. Thanks in advance!

What if the mystery of unified theory is solved (i.e we found a TOE)? What would be the next mystery in physics(will their be any or will the context of physics would be completed(i don't think so,what do you think?).

Urs Schreiber submitted a new PF Insights post Introduction to Perturbative Quantum Field Theory Continue reading the Original PF Insights Post.

Homework Statement Prove that if ##A \subseteq B##, then ##\bigcup A \subseteq \bigcup B##. Homework EquationsThe Attempt at a Solution This is a simple problem, but I just want to make sure I am writing out the proof correctly: Suppose that ##A \subseteq B##. We want to show that ##\bigcup A...

Does General Relativity predicts that in the early universe vacuum energy was converted into matter? How does it relates to the Inflation Theory by Allan Guth? I'm asking this because I remember reading in a book on GR that there are ways of calculating the total amount of energy in the...

Hey so from my understanding of Einsteins theory of relativity the closer you travel to the speed of light the slower time is for you, is that right? if it is right does that give to reason that there could be a critical speed past the speed of light for which time for the object traveling at...

Homework Statement Assume that ##x## and ##y## are members of a set ##B##. Show that ##\{ \{x\}, \{x,y\} \} \in \mathcal{P} \mathcal{P} B## Homework EquationsThe Attempt at a Solution I know that ##\{ \{x\}, \{x,y\} \} \in \mathcal{P} \mathcal{P} B## iff ##\{ \{x\}, \{x,y\} \} \subseteq...

Physicists had success in developing a relativistic quantum mechanics, also Quantum Field theory. I wonder why it's not the same with a quantum gravity theory. I suppose this is mainly because we do not have good emphirical information from a place where Einstein's theory fails: black holes...

Is there any theory law explaining the nature of space and describing what is space and what happens to space when some event take place in space.

Hello, I have read somewhere that the next major step in physics will be unifying general relativity with the quantum theory. Does anyone know about such? I wanted to know a bit more. I have read about such in the book by Stephen Hawking "A Brief History of Time". Thanks, I. P.S. My apologies...

Homework Statement Show that ##\bigcup \{\mathcal{P} X : X \in A \} \subseteq \mathcal{P} \bigcup A## Homework EquationsThe Attempt at a Solution Suppose that ##c \in \bigcup \{\mathcal{P} X : X \in A \}##. Then by definition this means that ##\exists a \in A## such that ##c \in \mathcal{P}...

I know two essential points where General Relativity plays a central role in String Theory: i) definition of the theory using a target spacetime with some Riemannian background metric in the Polyakov action and ii) recovery of the Einstein field equations as conditions regarding conformal...

Homework Statement In analogy to the Bohr theory of the hydrogen atom, develop a quantum theory of Earth satellites, obtaining expressions for the orbit radius, r_n, and the energy, E_n in terms of the quantum number n and other relevant parameters. Use the "Old" Quantum Theory. A satellite of...

Just out of curiosity, what would a proof of ##a^m a^n = a^{m+n}## amount to? Of course obviously if you have n of one thing and m of another you get m+n, but I am wondering if this is rigorous enough, or if you need induction.

Hello all; this my first time ever taking physics, and I am in dire need of some help with homework. I've had an attempt at part A (please take a look and provide feedback), but have no clue where to even begin on part B (how would I go about calculating questions 5, 6, and 7, to be precise?)...

What's the difference between relativistic quantum mechanics and quantum field theory? In principle, my guess is that to do the former, one needs to express the Hamiltonian in a relativistic, Lorentz invariant, form, because it seems to be the only frame-related term in the wave equation. (Is...

I have some questions about scalar field Lagrangians, using the box notation defined as \Box \equiv \frac{\partial^2}{\partial t^2} - \nabla^2 . It's a basic, perhaps silly issue, but somehow I've managed to sweep it under the rug for a long time. So, usually, the Lagrangian of a free scalar...

Hello! Recently I found this article: http://quantum-journal.org/papers/q-2017-07-14-13/pdf/ Being familiar with some basis of quantum formalism, I, nevertheless, experienced several difficulties with understanding of the theorem described in this paper. I would really appreciate if someone...

And if I can extend this further, for liquids?

In the multiverse theory, I keep on hearing that our observable universe is one of many universes. Is that saying that our universe ends at the point we can no longer see it - at the end of the observable universe. That would mean that the Earth is the literal centre of our universe. Am I...

I'm interested in the the band theory of solids for semiconductor modeling. I haven't solved the Schrodinger equation for multiple atoms, but I'd like to know some details that experienced physicists might already know. Several texts show how the bands develop from molecular coupling of...

According to classical electromagnetic theory,for acceleration a particle must not only change its direction but it should also increase its speed. But Maxwell said that a particle accelerates then it radiates energy.(this is with reference to Rutherford model). But actually the particle is not...

Hello. I will be attending a course on Group theory and the book that the professor suggests is Georgi's Lie Algebras in Particle Physics. As I liked Zee's book on General Relativity, I thought that it would be a blast to also use his Group theory textbook for the course. Problem is that I don't...

I just wanted to share this idea with other people who may be interested: I watched a PBS Space Time episode about the speed of light more accurately described as the speed of causality. And I Submit! That "time" is simply a interaction between atoms. And though an interaction can be...

Hello! I am reading some representation theory (the book is Lie Algebra in Particle Physics, by Georgi, part 1.17) and the author solves a problem of 3 bodies connected by springs forming a triangle, aiming to find the normal modes. He builds a 6 dimensional vector formed of the 3 particles and...

Homework Statement ##1)## Which one of the following is an example of a set ##S## such that the language ##S^*## has the same number of 8-letter words as 4-letter words? 1) ##S = \{aaaa \quad bbbb\}## 2) ##S = \{bbbb \quad bbbbbb\}## 3) ##S = \{aa \quad bb\}## 4) ##S = \{a \quad bbbb\}##...

We can prove that When A and B are two sets(A≠B) (A-B) = (A∩B') = (A-(A∩B)) {We can also confirm them using venn diagram} From first and third relation A-B = A - (A∩B) By cancelling A from both side I get B = (A∩B) Which is only possible when A and B are same set. What is wrong in my proof , is...

My physics teacher, who dislikes the idea of dark matter, told me that a physicist created an alternative explanation to the phenomena caused by dark matter. Is there something I missed on the news? What is the alternative theory to dark matter and how does it explain 'things' ?

Hi everyone, I have a question that, when came to me, sounded a bit silly to me as well, but then I realized, I myself maybe don't understand the logic behind this 100%, so why not discussing with you about it. So my question is the following. Usually we are used to do quantum field theory...

Emission theories propose that the velocity of light depends on the velocity of the light source. But the ordinary Doppler effect assumes the velocity of light remains as ##c## with respect to the ether medium, even when the light source is moving at speed ##v## with respect to the ether. They...

I saw a documentary the other day where Michio Kaku said something that really peaked my interest. He said that Einstein in his last days was working on something having to do with how small geometries of some sort being the cause of gravity. Does anyone know the details of Einstein's Unified...

Hello everyone! I'm studying the physics of complex systems and I'm approaching probability theory. I understand that we need a ## \sigma-algebra ## and the Kolmogorov axioms in order to define a probability space but then I bumped into the following relation: $$ p(A_1 \cup A_2 ) = p( A_1 ) + p(...

I'm not a math machine, but I dabble in dimensional stuff. I think this falls under knot theory. I have built several prototypes of a tesseract. Each of them sits in a little case in my office. One of them is made from truncated cubes, held together with elastic cord: In theory, the...

I've been studying TQFT and gauge theory. Dijkgraaf-Witten theory in particular. One learns that a topological field theory applied to a manifold outputs the number of principal G bundles of a manifold. My question is for the Physicists in the room, why do you want to know the number of...

Homework Statement Homework EquationsThe Attempt at a Solution [/B] I think I understand part b) . The idea is to move the operator that annihilates to the RHS via the commutator relation. However I can't seem to get part a. I have: ## [ P^u, P^v]= \int \int \frac{1}{(2\pi)^6} d^3k d^3 k'...

Homework Statement Action attached: To find the EoM of ##\phi ## / ##\phi^* ## Homework Equations The Attempt at a Solution [/B] Without deriving from first principles, using E-L equations I have: ## \partial_{u}\frac{\partial L}{\partial_u \phi} - \frac{\partial L}{\partial \phi} =0 ##...

I study control theory and robotics. Recently I figured out that I have a much deeper understanding of probability and statistics compared to my colleagues. Is this 'talent' valuable in my field and if so, where? We used this theory to define white noise, but nothing more...as of now. Also I am...

Urs Schreiber submitted a new PF Insights post Super p-Brane Theory Emerging from Super Homotopy Theory Continue reading the Original PF Insights Post.

Hi everyone, I remember years ago at school memorising the derivation of the formula for pressure in the kinetic theory of gases, as explained in this Youtube video: Thinking a little more deeply about this derivation there are two things I don't get: 1) At 0:53, the video says the molecule...

Suppose there is a charged particle far enough of any mass so that there is no gravitational interaction between the particle and any other body. The trajectory of the particle in space-time would appear to us like this (we are at the origin of our coordinate system). Consider that at...

1. Homework Statement Hello all. It is not a homework actually. I just didn't know at which forum I should post. I am working on a MATLAB code solving the finite wing properties iteratively by using the Anderson's Numerical Lifting Line Method. However, I got some wrong results. The...

Hi there. It is well known from the theory of differential equation the Sturm-Liouville theory, concerning with the eigenvalue problem: ##\displaystyle \frac{d}{dx} \left ( p(x) \frac{dy_n}{dx} \right ) - q(x) y_n(x)=\lambda_n w(x) y_n(x)## with prescribed boundary condtitions for ##a\leq x...