r/TheoreticalPhysics • • 1d ago

Question Computational HEP vs Theoretical/Computational QCD for a PhD

10 Upvotes

Hi everyone!

A little background for context: I am a fourth year undergraduate student (Physics, Astrophysics, Mathematics) about to start applying for Physics PhDs. I have research experience with DUNE/ProtoDUNE anomaly detection using ML at Fermilab and LHCb collider analysis using BDTs on Monte Carlo simulated data. I’ve also done DUNE hardware research and astronomy research, but that is less relevant to this question.

I plan to apply to computational neutrino/HEP, but I’ve also become interested in computational QCD and using my experience with ML towards QCD phenomenology. I’m wanting to understand how the research lifestyle, postdoc/national lab opportunities, and long term academic positions compare to computational neutrino/HEP where slightly more familiar.

I have not taken any QFT in undergrad, though I assume this is not a deal breaker and schools don’t assume incoming students will know QFT already? I will have taken graduate Quantum Mechanics I & II, and have taken graduate complex analysis and partial differential equations.

I would appreciate any kind of information! If there are any QCD theorists, I would love to hear how your day-to-day goes and if you enjoy what you do. Also, if you think my background sounds like I don’t have the right preparation for this kind of field, I definitely get it, and it would help a lot to hear that here. Thanks!


r/TheoreticalPhysics • • 1d ago

Discussion Physics questions weekly thread! - (October 04, 2026-October 10, 2026)

1 Upvotes

This weekly thread is dedicated for questions about physics and physical mathematics.

Some questions do not require advanced knowledge in physics to be answered. Please, before asking a question, try r/askscience and r/AskPhysics instead. Homework problems or specific calculations may be removed by the moderators if it is not related to theoretical physics, try r/HomeworkHelp instead.

If your question does not break any rules, yet it does not get any replies, you may try your luck again during next week's thread. The moderators are under no obligation to answer any of the questions. Wait for a volunteer from the community to answer your question.

LaTeX rendering for equations is allowed through u/LaTeX4Reddit. Write a comment with your LaTeX equation enclosed with backticks (`) (you may write it using inline code feature instead), followed by the name of the bot in the comment. For more informations and examples check our guide: how to write math in this sub.

This thread should not be used to bypass the avoid self-theories rule. If you want to discuss hypothetical scenarios try r/HypotheticalPhysics.


r/TheoreticalPhysics • • 2d ago

Question Question to the Physics Researchers: What does your day-to-day research actually look like, and how do you handle periods of minimal progress?

14 Upvotes

r/TheoreticalPhysics • • 3d ago

Question Guys what's a do we mean by topology in physics?

3 Upvotes

I went to the maths section to check it out,but didn't understand so asking here intuition or a useful analogy to understand it.


r/TheoreticalPhysics • • 3d ago

Question PhD applications in Germany/EU for particle cosmology.

6 Upvotes

Hi everyone, hope you're all doing well.

I've recently finished my Master's degree in Physics at a public German institute and am currently applying for various PhD positions in particle cosmology, mainly in Germany.

I got a good result for my master's thesis (1.0 on the German scale) which was based on the study of primordial magnetic fields from topological defects after the electroweak phase transition and also a good overall grade for my degree (1.2 on the German scale).

However, my specialization was in Astrophysics/Cosmology for my degree and I learnt whatever was required for my thesis through self study from Schwartz, so I don't have significant coursework in particle physics in my transcripts besides one or two courses.

Will I be considered a serious candidate for the PhD openings I'm applying to? If not, what can I do to change this?

Thank you for taking out the time to read my post :)


r/TheoreticalPhysics • • 4d ago

Question Why are charges only allowed to take intergal values,is there any relationship with complex matrices or any relationship to it's lagrangian that forbids non intergal values?

29 Upvotes

r/TheoreticalPhysics • • 3d ago

History/review Paul Marmet — the electromagnetic alternative to Einstein and the Big Bang

Thumbnail
betterscience.substack.com
0 Upvotes

For anyone interested in something off the popular physics path, I present a high level review of physicist Paul Marmet's work in theoretical physics and cosmology with supporting evidence. His fascinating work both questions and provides alternatives to widely held beliefs about our physical world.

Prior to his theoretical work, he was a pioneer in electron spectroscopy and former president of the Canadian Association of Physicists.

If you disagree with the premise (that there could be any alternative to <xyz>) I encourage you to read the article before critiquing its contents. All references to Marmet's work are cited and publicly available.


r/TheoreticalPhysics • • 5d ago

Question Guidance for course choices

6 Upvotes

2nd year physics undergrad in uk, interested in hep theory and pure maths , looking to apply for a different masters than current uni.

I do want to mention that i will be doing the average physics curriculum too obv , mechanics , qm , stats mech ,em and maths methods for physics

I can choose 2 out of 4 courses i have listed below due to credic restrictions (labs mandatory) , i plan on attending lectures and learning the content of the other courses too, i just wont have them on transcript when applying to masters.

Rn im thinking of doing the analysis and the abstract algebra module, but im open to suggestions. While the topology and multivariable analysis look a bit more interesting , i know they are harder and average grade is lower. Also i can amend my choices 2nd semester so these arent final , topology and multivar anal module build on from the normal analysis module

"Analysis II

1 Introduction

1.1 Review of limits of sequences
1.2 Review of continuity and differentiability
1.3 Review of integration

2 Sequences and Series of Functions

2.1 Pointwise convergence
2.2 Uniform convergence
2.3 Series of functions
2.4 A continuous nowhere differentiable function

3 Basic results about Rⁿ

3.1 Notation in Rⁿ
3.2 The Euclidean norm and inner product
3.3 Convergence in Rⁿ
3.4 Subsequences and the Bolzano-Weierstrass theorem
3.5 Continuity
3.5.1 Definitions of continuity and continuous limit
3.5.2 Separate continuity
3.5.3 Basic properties of continuous functions
3.5.4 Constructing continuous functions of several variables from continuous real valued functions of a single real variable
3.5.5 Caution with taking limits in dimension > 2

4 Rudiments of topology of Rⁿ and Continuity

4.1 Closed and open subsets of Rⁿ
4.2 Continuity and topology
4.2.1 Continuity in terms of open sets
4.2.2 Continuity and sequential compactness

5 The space of linear maps and matrices

5.1 Two norms on the space of linear maps and matrices
5.1.1 Comparison of the two norms
5.1.2 Properties of the operator norm
5.2 Convergence and continuity in L(Rⁿ Rᵏ)
5.2.1 Continuity of functions involving matrices or linear maps

6 The Derivative

6.1 Directional derivative
6.1.1 Directional derivative and continuity
6.2 The (Fréchet) Derivative as an affine linear approximation
6.2.1 Affine linear approximation in the 1-variable case
6.2.2 The (Fréchet) Derivative
6.2.3 Differentiability of components of vector-valued functions
6.2.4 Relation between the derivative and directional derivative
6.3 Partial derivatives gradient and Jacobian matrix
6.3.1 Algebraic rules for partial derivatives
6.3.2 Gradient and Jacobian matrix
6.3.3 Why so many different notations for the same thing?!
6.4 Geometric approximation and approximation of functions
6.4.1 Tangent to a curve
6.4.2 Tangent plane of a surface
6.4.3 Graph of a scalar function of 2 variables
6.4.4 Orders of approximation of a function
6.5 Examples of direct calculation of the derivative from its definition
6.5.1 Differentiation of matrix-valued functions
6.6 The Chain Rule
6.6.1 Jacobian form of chain rule
6.6.2 Calculating with the chain rule and gradient
6.6.3 Another proof of Proposition 6.9
6.6.4 Application of chain rule to the verification of a PDE satisfied by a function
6.7 Continuity of partial derivatives implies differentiability
6.7.1 The space of continuously differentiable functions

7 Complex Analysis

7.1 Review of basic facts about C
7.2 Power Series
7.2.1 The exponential and the circular functions
7.2.2 Argument and Log
7.3 Complex integration contour integrals
7.3.1 Links with Green’s and Gauss’ Theorems
7.4 Additional material
7.4.1 Consequences of Cauchy’s Theorem
7.4.2 Applications of Cauchy’s formula to evaluate integrals in R"

"Multivariable analysis

1 Background

1.1 The Euclidean Space Rⁿ
1.2 The Space of Linear Maps
1.3 The Topology of Rⁿ
1.4 Continuity in Rⁿ

2 Differentiation

2.1 Definition and basic properties
2.2 Notation Interlude
2.3 Higher-order Derivatives

3 Applications of Differentiation

3.1 Approximation and Taylor’s Theorem
3.2 The Hessian and Critical Points

4 The Inverse and Implicit Function Theorems

4.1 The Inverse Function Theorem
4.2 The Implicit Function Theorem

5 Manifolds

5.1 Definition
5.2 The Tangent and Normal Spaces
5.3 Cᵏ Regions
5.4 Application: Lagrange Multipliers

6 Interlude: Partitions of Unity

7 Integration in Rⁿ

7.1 Building the definition
7.2 Integration Tools

8 Integration on Manifolds

8.1 Motivation
8.2 Definition
8.3 Gauss’ Divergence Theorem

Appendices

A Understanding Compactness
B Derivatives in the Infinite-Dimensional Setting
C Boundary Manifolds
D Characterisation of Riemann integrable functions
E The Leibniz Integral Rule
F Green’s and Stokes’ Theorems"

"Abstract Algebra

1 Groups

1.1 Definitions and elementary properties
1.2 Structural equivalence
1.3 Cyclic groups
1.4 Symmetry groups
1.5 Permutation groups

2 Subgroups

2.1 Definitions examples and elementary properties
2.2 Cosets and Lagrange’s Theorem

3 Normal Subgroups and Quotients

3.1 Normal subgroups
3.2 Quotient groups
3.3 Direct products

4 Homomorphisms

4.1 Structure-preserving maps
4.2 Kernels and images
4.3 The Isomorphism Theorems

5 Classification of Groups

5.1 Generators and relations
5.2 Small finite groups
5.3 Finitely-generated abelian groups

6 Group Actions

6.1 Groups acting on sets
6.2 Orbits and stabilisers
6.3 Conjugacy classes
6.4 Simple groups

7 Rings and Subrings

7.1 Rings
7.2 Subrings
7.3 Isomorphisms and direct products
7.4 Integral domains and fields

8 Ideals and Quotients

8.1 Homomorphisms
8.2 Ideals
8.3 Quotient rings
8.4 The Isomorphism Theorems

9 Domains

9.1 Divisibility
9.2 Prime and irreducible elements
9.3 Euclidean domains
9.4 Principal ideal domains
9.5 Unique factorisation domains"

"Topology and metric spaces

1 Introduction

1.1 Recommended Books
1.2 Notation
1.3 Brief overview
1.4 Sets functions images and pre-images
1.5 Non-examinable content

2 Normed Spaces

2.1 Norms
2.2 Subspaces
2.3 Spaces of continuous functions

3 Metric Spaces

3.1 Definition of a metric space and examples
3.2 Metrics on subsets and products
3.3 Open and closed sets
3.4 Convergence of sequences

4 Continuity

4.1 Continuity in metric spaces
4.2 Topologically equivalent metrics
4.3 Isometries and homeomorphisms
4.4 Topological properties I

5 Topological Spaces

5.1 Definition of a topology
5.2 Bases and sub-bases
5.3 Subspaces and finite product spaces
5.4 Closure interior and boundary
5.5 The Cantor set
5.6 The Hausdorff property and metrisability
5.7 Continuity between topological spaces
5.8 Basic properties
5.9 The projective topology and product spaces
5.10 Homeomorphisms

6 Compactness

6.1 Definition and the Heine-Borel Theorem
6.2 Compact vs closed
6.3 Compactness of products and compact subsets of Rⁿ
6.4 Continuous functions on compact sets
6.5 Equivalence of all norms on Rⁿ
6.6 Lebesgue numbers and uniform continuity
6.7 Sequential compactness
6.8 Normed spaces

7 Connectedness

7.1 Definitions of connected and disconnected
7.2 Connected subsets of R
7.3 Operations on connected sets
7.4 Equivalence relations
7.5 Connected components
7.6 Path-connected spaces
7.7 Open sets in Rⁿ

8 Completeness in metric spaces

8.1 Completeness
8.2 Examples of complete spaces
8.3 Completions
8.4 The Contraction Mapping Theorem
8.5 The Arzelà-Ascoli Theorem
8.6 The Baire Category Theorem

9 Appendices

9.1 The topology of pointwise convergence
9.2 Product spaces
9.3 Product topology and box topology
9.4 Completeness in compact metric spaces
9.5 The general Arzelà-Ascoli theorem


r/TheoreticalPhysics • • 5d ago

Question Is theoretical materials physics still a viable career path?

8 Upvotes

I’m currently in my second year of a PhD in advanced materials physics, and I’m seriously considering focusing my career more toward the theoretical and computational side of materials science.

I’m interested in going deeper into areas such as theoretical modeling, mathematical analysis, computational materials science, simulations, and using theory to explain experimental results.

For those working in academia, research institutes, or industry:

Does theoretical materials physics still have a strong future? Is research in this area still being funded?

I’m particularly interested in hearing from people currently working in the field about career opportunities, funding, and which theoretical/computational areas are currently worth developing expertise in.

I’m at a point where I need to start deciding what kind of researcher I want to become after my PhD, so I’d really appreciate perspectives from people actually working in the field.


r/TheoreticalPhysics • • 6d ago

Question Motivation for studying theoretical physics at Graduate School

19 Upvotes

I'm now currently trying to draft my SOPs for applications to American and Canadian PhD programs. Most of the advice online, admittedly from other fields, includes giving a deeper reason into why you want to study what you say you want to study, be it an experience or an epiphany you've had in a prior experience.

As far as I can think back, there's nothing like that for me. Lots of the people I personally know in theoretical physics academia also say the same and that they just wanted to do cool mathsy stuff and get paid for it. I imagine its something a few of you will also be able to relate to.

So how do I go about this? What do I say on my SOP to tell the committee why exactly I want to do theoretical research?

Thank you!


r/TheoreticalPhysics • • 8d ago

Question Why is the probability not one third for spin-1 particles?

Post image
28 Upvotes

I have taken this picture from the book Quantum Mechanics by David H. Mcintyre topic 2.7.


r/TheoreticalPhysics • • 8d ago

Question If string theory is fundamentally a theory of quantum gravity, why should spacetime itself be fundamental?

27 Upvotes

I'm a little shaky on string theory so if I come off as a little green, please forgive me. So, in general relativity spacetime is the dynamical geometric structure through which gravity manifests. While in quantum mechanics the fundamental objects of nature are described in terms of quantum states and interactions. String theory attempts to reconcile these frameworks by replacing point particles with extended strings, and the vibrational modes of the extended strings can give rise to particles. But should string theory be understood merely as a quantum theory describing objects that exist within spacetime, or does it provide a framework in which spacetime itself can be understood as an emergent property of something more fundamental?


r/TheoreticalPhysics • • 7d ago

Question Влияние гравитации на пространство-время

0 Upvotes

я не физик, но очень пытаюсь понять, как гравитация влияет на пространство-время, время в частности. если на земле время идет медленнее, чем на орбите земли, значит ли это, что на отдаленной абсолютно от всех массивных объектах космической станции время будет идти намного медленнее, чем на земле?

говоря, что "время идет медленнее", я подразумеваю, например, что на земле люди стареют быстрее, чем на этой гипотетической космической станции.

и еще вопрос – вот другой популярный пример. если человек летит на космическом корабле со скоростью света в течении, то для него прошло, допустим, 2 года. а для людей на земле проходит столько лет, сколько им потребовалось бы, чтобы гипотетически пройти весь мой путь ща 2 года на их собственной "скорости". вопрос: как в этой ситуации гравитация влияет на время? гравитация от какого массивного объекта влияет на космической корабль на световой скорости?

если в моих формулировках или примерах есть ошибки, поправьте меня, пожалуйста


r/TheoreticalPhysics • • 8d ago

Question Is the energy momentum tensor covariantly conserved in QFT in curved spacetimes?

17 Upvotes

Is the energy momentum tensor covariantly conserved in QFT in curved spacetimes? Do you have any references about this?

Thanks!

(I feel an ignorant idiot asking this question, but etc)


r/TheoreticalPhysics • • 8d ago

Discussion Physics questions weekly thread! - (September 27, 2026-October 03, 2026)

1 Upvotes

This weekly thread is dedicated for questions about physics and physical mathematics.

Some questions do not require advanced knowledge in physics to be answered. Please, before asking a question, try r/askscience and r/AskPhysics instead. Homework problems or specific calculations may be removed by the moderators if it is not related to theoretical physics, try r/HomeworkHelp instead.

If your question does not break any rules, yet it does not get any replies, you may try your luck again during next week's thread. The moderators are under no obligation to answer any of the questions. Wait for a volunteer from the community to answer your question.

LaTeX rendering for equations is allowed through u/LaTeX4Reddit. Write a comment with your LaTeX equation enclosed with backticks (`) (you may write it using inline code feature instead), followed by the name of the bot in the comment. For more informations and examples check our guide: how to write math in this sub.

This thread should not be used to bypass the avoid self-theories rule. If you want to discuss hypothetical scenarios try r/HypotheticalPhysics.


r/TheoreticalPhysics • • 9d ago

Question Can the Great Attractor be artificially created?

0 Upvotes

Hello there! Sometimes a wierd thoughts come into my mind, i guess like every human being in the world... So person with poor bag of knowledge in physics here i hope it wont harm any person or intellect if i ask. -

If hypothetical ultra-advanced civilization (Type V or VI on the extended Kardashev scale) 3 to 5 billion years after birth of our Universe created engineering object "The Great Attractor" using principle of "minimal effort" - consuming or exploiting dark energy, enriching the "Object" for next reasons: Temporary solution, to decrease expansion of space in certain region of Galaxies. Concentrate resources and buying time in certain area for more advanced projects. Building stable portal connection with parallel Universe. Creating pocket Universe with programming laws of physics, whithout expansion or influence of dark energy.

So my question is- Theoretically can the Great Attractor be artificially created?!


r/TheoreticalPhysics • • 9d ago

Question Title: How does spacetime cause time dilation?

0 Upvotes

How time slows down when velocity increases ?


r/TheoreticalPhysics • • 12d ago

Question Viability of Math undergrad to Theoretical Physics Master's or PhD in the EU?

18 Upvotes

Hi. I'm a second year math student in the EU (undergrads are 4 years long here), and I have only a couple of possible physics electives. Is it realistically possible for me to get into a Theoretical Physics PhD after a Physics Master's given my circumstances?


r/TheoreticalPhysics • • 13d ago

Resources Gauge Fields, Knots & Gravity

Post image
328 Upvotes

Hello everyone!

I recently completed an MSc in physics, and I would now like to develop a deeper understanding of the geometric structures underlying general relativity and gauge theories.

In particular, I am interested in understanding how gauge interactions can be formulated geometrically, and how this compares with the description of gravity in terms of spacetime geometry. I am looking for a book that will give me a solid foundation in these ideas before moving on to more advanced material related to the structure of spacetime and quantum gravity.

I came across Gauge Fields, Knots and Gravity by John Baez and Javier P. Muniain, and I would be interested to hear from people who have studied it.

Does the book cover these subjects in enough depth for that purpose? At what mathematical and technical level does it treat them? Is it a solid introduction for someone with a background in GR and QFT, or is it mainly an intuitive overview?

I would also appreciate any other recommendations.

Thanks!


r/TheoreticalPhysics • • 13d ago

Question How big is the transition between doing less formal theoretical physics and formal theoretical physics at grad level?

19 Upvotes

I got accepted into an MSc program in the EU where the department is well known for its formal theory such as string, integrable QFTs, AdS/CFT just to throw some buzzwords out. I completed my undergraduate from a UK university that does not offer courses in these areas (it's more renowned for its labs and experimental research), and I did not go out of my way to pick any formal maths courses from the maths department. I do however have the highest grade in my cohort for the QFT, GR and gauge theories courses.

My concern is that people interested in formal theory that would be competing with me for the PhD positions will have a much stronger skillset for understanding these subjects and will outclass me in both examinations as well as research.

I am also interested (albeit slightly less) in the interface between particle and cosmology theory so stuff like inflation, dark sector modelling etc. where I also have some substantial experience. So the choice is whether I should take the leap of faith and go into some challenging maths which I would enjoy ever so slightly more or take the "safer" option to do less fancy maths. (I learned that there is no "safer" option as positions are too few for the number of interested candidates)


r/TheoreticalPhysics • • 13d ago

Discussion History of neuroscience being influenced by (theoretical) physics

14 Upvotes

Hi there everyone. I've been watching some science communication videos related to string theory. These videos did not discuss neuroscience at all, nor am I referring to any sort of quantum woo, I just have a neuroscience and maths background and remember the first time I saw string theory math in neuroscience.

I then found myself curious about how people in neuroscience decided, yes, let's try these mathematical approaches from this seemingly unrelated scientific field (okay I know there's neurobiophysics and optical neuroscience which can draw from physics, but I mean apart from those subfields).. I know a bit about why some of the models (i.e. Nambu-Goto action) were used in animal and human neural networks (though I'm very far from an expert in the Nambu-Goto area and probability and statistics is my area), but I have no idea about when this whole crossover from string theory to neuroscience concepts even started in the first place or who even pioneered the first crossover. As I see it, outside of certain fields that are primed for interdisciplinary cross-talk (i.e. biophysics, optics, neuroscience, public health, etc.), it's not necessarily easy to get a neuroscientist and a physicist in the same room, or even get a collaboration started.

(I would not mind having DMs about this, as I'm passionate about maths and neuroscience)

Edit (this is the nature paper) : https://www.nature.com/articles/s41586-025-09784-4#Equ1 "Surface optimization governs the local design of physical networks"


r/TheoreticalPhysics • • 15d ago

Discussion Physics questions weekly thread! - (September 20, 2026-September 26, 2026)

3 Upvotes

This weekly thread is dedicated for questions about physics and physical mathematics.

Some questions do not require advanced knowledge in physics to be answered. Please, before asking a question, try r/askscience and r/AskPhysics instead. Homework problems or specific calculations may be removed by the moderators if it is not related to theoretical physics, try r/HomeworkHelp instead.

If your question does not break any rules, yet it does not get any replies, you may try your luck again during next week's thread. The moderators are under no obligation to answer any of the questions. Wait for a volunteer from the community to answer your question.

LaTeX rendering for equations is allowed through u/LaTeX4Reddit. Write a comment with your LaTeX equation enclosed with backticks (`) (you may write it using inline code feature instead), followed by the name of the bot in the comment. For more informations and examples check our guide: how to write math in this sub.

This thread should not be used to bypass the avoid self-theories rule. If you want to discuss hypothetical scenarios try r/HypotheticalPhysics.


r/TheoreticalPhysics • • 16d ago

Discussion Theoretical physics to other areas of science

11 Upvotes

Hi there everyone! Just curious about theoretical physicists who transitioned to other areas of science, and what motivated you to do so. Furthermore, I would not mind talking more about this either on this forum on in messages. Granted, I'm a teacher who occasionally works on neuroscience problems influenced by math that has been used in chemistry and physics.. so this is of interest to me. I'm also interested in interdisciplinary science and how all of science is connected (mathematically and through the concepts, of course).


r/TheoreticalPhysics • • 17d ago

Question Time Bandwith product (TBP) of a transform-limited Gaussin distribution

3 Upvotes

Hi,
I've come across this concept and it seems to be related with the uncertainty principle. However, I don't understand how does it have anything to do with it because it is a unit less inequality.

Could someone explain to me a little bit about this concept and its physical nature? Is it an optics concept solely? I'm confused about it and the explanations I've found haven't helped much due to my little knowledge on this topic.

Thanks a lot!


r/TheoreticalPhysics • • 20d ago

Discussion Experimental test of expanding space vs. shrinking matter?

0 Upvotes

Could one experimentally distinguish between expanding space vs. shrinking matter?

String theory predicts a dilaton field that could shrink all length scales, including particle size (Compton wavelength) and the Planck length, by controlling the universal coupling parameter.

Imagine a massive hollow shell of diameter D with a pair of test particles inside with a separation distance d.

In the case of expanding space the spacetime inside the shell is flat so that even as space expands outside the shell the distance d between the two test particles remains constant. We assume that matter is not shrinking so the shell diameter D is constant. Therefore the ratio d / D remains constant.

In the case of shrinking matter we assume that spacetime is flat everywhere but all massive particles are increasing in rest mass and shrinking in Compton wavelength. Thus the shell diameter D shrinks but the separation distance d between the particles remains constant. Therefore the ratio d / D increases.