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36

This is a tricky question because it asks about the meaning of words. People use the word "particle" to refer to various, not always well defined, notions in physics. In the end, I think the simplest and more correct single way to categorize the terms is to interpret "particle" as "excitation of a field". For example, if someone says "There are two ...


10

What follows is an answer from an experimental particle physicist, i.e. one who has more knowledge of theoretical physics than the average educated person, but not in a position to teach it :). I can use theoretical results and study data and validate or falsify a theory. I would like to know that if what we conceptualize as a "field" is merely an ...


7

When I studied quantum mechanics, my professor advised that I avoid the question "which is more fundamental?" and replace it with "which is more useful?". The problem is that our brains are programmed to think classically, so many concepts in QM have no classical analogue. For that reason, we usually discuss them mathematically in order to avoid ambiguity. ...


5

The ADS database contains 11 million records of publications in astronomy, physics and geophysics, as well as arXiv preprints.


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SSC: synchrotron self-Compton BBC: Compton upscattered blackbody radiation; Compton upscattering of stellar blackbody photons XC: upscattering of photons emitted by the accretion flow; accretion flow photons From: http://arxiv.org/abs/1307.1309 and http://arxiv.org/abs/1403.4768


4

The quote continues: "He knows that they are all equivalent, and that nobody is ever going to be able to decide which one is right..." So I don't think classical gravitation versus generally relativity is a good example, because they can be distinguished experimentally. Perhaps the Schrodinger versus Heisenberg formulations of quantum mechanics.


3

To study the precise mathematical formulation of path integrals, you actually need probabilistic tools. The path integral is a stochastic integral with suitable measures, such as the Wiener measure associated with brownian motion. The ideas used by physicists are very useful, but not always mathematically accurate, and rely more or less on justification by ...


3

I'll take a stab at each of your questions one by one: How does the research in theoretical physics differ from mathematics? Research in physics and research in mathematics are very different activities. While they both use mathematics as a tool to communicate ideas, they are doing so to accomplish very different goals. Remember that conclusions in ...


3

First, you can be sure that a PhD student will almost always work on a very particular and nuanced topic in either of the fields. Even if you do a PhD in string theory, you might just ask about some very specific class of solution or about a prediction of observation of a very special measurement. It is hard to find "big" questions which haven't been asked ...


3

Batteries contain various liquids that are important for the voltage to be produced. Sometimes, the liquid – even water – may turn to gas and it is permanently lost, along with the capacity. Sometimes, the liquid just moves to one side of the battery which is also bad. Shaking a weak battery may homogenize the concentration of the liquid across the battery. ...


3

I recommend two resources: Feynman's original book called Quantum Mechanics and Path Integrals. This contains most of the prerequisites in the first two chapters, but you will need some maturity to get through them. A. Zee's quantum field theory book Quantum Field Theory in a Nutshell for its friendly chapter on them.


2

Short answer: There is no such boundary. Longer one: Quantum Mechanics has been experimentally seen to work even at macroscopic size like neutron stars (whose stability is explained by Pauli's Exclusion Principle). Another example, conduction of macroscopic number of electrons in superconducting Josephson junction (whose BCS theory is purely quantum ...


2

The fundamental difference is, that the physicist can develop stuff based on heuristics and physical intuition, while the mathematician has to prove every single step he does. The work of justifying the stuff the theorist does, is again the mathematician's part, the theorist is happy as long as his theory works. For a nice example for the difference, I ...


2

I think you are just being a bit too broad in your categories. Take for example classical mechanics. Yes there is a broad split between newtonian and analytical mechanics, but within each of those there is a range of pictures you can use to understand a situation. On the analytic side there is the Lagrangian and Hamiltonian formulation. On the Newtonian side ...


2

We don't really understand why charge is quantized. Nor we do know if there ought to be magnetic monopoles. These two things seem linked. Dirac gave an argument for charge quantization in the early days, but this presupposed the existence of a magnetic monopole. In Maxwell's equations, it would be completely natural to imagine the existence of magnetic ...


2

The Wikipedia article on the Drake equation includes a section giving the current estimates for its parameters. I won't copy and paste the text here: suffice to say that $R_*$ and $f_p$ are reasonably well known. We're beginning to get a handle on $n_e$ from the exoplanet surveys. However we have little or no experimental evidence to assign values to any of ...


2

This question is a bit open-ended so I'm not sure if it's appropriate for this site, but I'll try to answer it anyway. What you're talking about most likely is developing so called 'maturity' in math and physics. This isn't really a well-defined concept, but most people have an intuitive sense of what it means; if you have maturity in physics this most ...


2

Work. Potential energy exists because of some force that exists, and moving an object relative to that force causes work to be done. And by the work-energy theorem, the work done on an object is equal to the change in kinetic energy of that object.


1

Feynman's path integral formulation is closely related to the action principle of classical mechanics, which relies heavily on the calculus of variations. You need to learn, essentially, how to minimize a functional. Prerequisites are pretty much just calculus (multivariable, hopefully), as well some classical mechanics to understand the motivation behind ...


1

I believe there is no complete database that would provide you with a reference to an authoritative review on every chosen topic. There are obviously journals mentioned by user just-learning that often provide high-quality reviews from people at the frontier of their area. These journals in which the most authoritative reviews independent of the field are ...


1

what about the arxiv? You can find a lot of papers even before the are published and also search by research area (hep-ph, th-ph,...) arxiv Google schoolar might help too.


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Try Microsoft Academic Search , it has huge section devoted to Physics and you can search by string query or authors and pay attention to review journals, where articles were published, as @just-learning suggested.


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Based on the Wiki article, we're looking at something on the order of millions for $N$ just in our galaxy. So far, we see there to only be us. This could be the result of a failure in the theory that led to the Drake Equation, or a lack of knowledge regarding the parameters. We really don't know too much regarding the parameters, thus extensive efforts are ...


1

Well, it is known that $N \geq 1$ (^o^) On a more serious note, the Kepler Space telescope is providing greatly improved estimates of the parameters $f_p$ and $n_e$.


1

To my knowledge, there isn't a specific term for these types of gasses. In your question you name "substance" while you list elements. Many different molecules are gaseous at room temperature; however, only a few of the elements are. I'll look at both. They come from different parts of the periodic table but do have a couple of features in common: ...


1

Just an extra thing to add: take a look at Feynman's wonderful point of view on this subject. It's very similar to what Daniel and Void answered, in my opinion- just more interesting (no offense to Daniel and Void- I think Feynman is more interesting than everyone!).


1

Quantum weirdness never stops to exist. Some quantum mechanical weirdness in theory could happen but the probability would be ridiculously small. There are just so many wavefunctions interacting with each other and the end result is modelled by Classical Mechanics as its approximation. When does this start to be apparent? When do you decide if you are going ...


1

This answer is just my opinion, but I think that if ever there were to be a Theory Of Everything, it would probably be radically different from any of the mainstream theories we currently have. As such it would have to incorporate all the experimental results of the mainstream, and that would be too big a task for one person. So collaboration is the obvious ...


1

Quantum Mechanics and Path Integrals: This is a book every physicist, or student of physics, should study. Here the author describes the principle of action in quantum physics. It is not a minimum action principle, like in classical mechanics: you can, however, derive the classical minimum principle from it, in the classical limit. Why is this important? ...


1

The real world is fundamentally quantum mechanical, just like it is fundamentally relativistic, but in certain limits it exhibits a different, simpler behavior. In the case of relativity there is a natural scale $c$, the speed of light, some constant of the universe. When we try to consider the physics that happens at speeds much smaller than this scale ...



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