Particle physics is the study of the fundamental forces of nature as they are embodied in the interactions of elementary and composite particles at high energies and short time and distance scales.
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6answers
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Why does space expansion not expand matter?
REFORMULATED:
I have looked at the other questions (ie "why does space expansion affect matter") but can't find the answer I am looking for.
My question:
There is always mention of space expanding ...
15
votes
6answers
4k views
What would be the effects on theoretical physics if neutrinos go faster than light?
Earlier today, I saw this link on Facebook about neutrinos going faster than the speed of light, and of course, re-posted. Since then, a couple of my friends have gotten into a discussion about what ...
41
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4answers
3k views
Gauge symmetry is not a symmetry?
I have read before in one of Seiberg's articles something like, that gauge symmetry is not a symmetry but a redundancy in our description, by introducing fake degrees of freedom to facilitate ...
25
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4answers
2k views
What is spin as it relates to subatomic particles?
I often hear about subatomic particles having a property called "spin" but also that it doesn't actually relate to spinning about an axis like you would think. Which particles have spin? What does ...
10
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9answers
3k views
Accelerating particles to speeds infinitesimally close to the speed of light?
I'm in a freshmen level physics class now, so I don't know much, but something I heard today intrigued me. My TA was talking about how at the research facility he worked at, they were able to ...
9
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2answers
3k views
How does the Higgs mechanism work?
I'm not a particle physicist, but I did manage to get through the Feynman lectures without getting too lost.
Is there a way to explain how the Higgs field works, in a way that people like me might ...
8
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1answer
484 views
How does one experimentally determine chirality, helicity, spin and angular momentum?
If I've got an instance of a fundamental particle, how can I separate out the measurements of these three concepts?
(I think) I understand the theory behind them, and why the particles in the ...
9
votes
4answers
815 views
Is there an accepted analogy/conceptual aid for the Higgs field?
Is there an accepted analogy / conceptual aid for the Higgs field?
In Physics there are many accepted conceptual aids such as
* Schrödinger's cat
* Maxwell's Demon
* I'm sure I'm missing ...
15
votes
8answers
9k views
Is anti-matter matter going backwards in time?
Or: can it be proved that anti-matter definitely is nót matter going backwards in time?
From wikipedia:
[There is considerable speculation as to why the observable universe is apparently almost ...
15
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3answers
891 views
Are elementary particles actually more elementary than quasiparticles?
Quarks and leptons are considered elementary particles, while phonons, holes, and solitons are quasiparticles.
In light of emergent phenomena, such as fractionally charged particles in fractional ...
13
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5answers
4k views
Is there an equation for the strong nuclear force?
The equation describing the force due to gravity is $$F = G \frac{m_1 m_2}{r^2}.$$ Similarly the force due to the electrostatic force is $$F = k \frac{q_1 q_2}{r^2}.$$
Is there a similar equation ...
4
votes
1answer
586 views
What is the relationship between string net theory and string / M-theory?
I've just learned from this one of Prof. Wen's answers that there exists a theory called string net theory. Since I've never heard about this before it picks my curiosity, so I`d like to ask some ...
15
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2answers
1k views
What happened to the idea of tachyonic or other superluminal neutrinos?
While hunting around for information about the recent OPERA measurement that hints at superluminal neutrinos, I discovered that this idea was actually considered back in the 1980s. Wikipedia lists as ...
11
votes
2answers
395 views
What is the mass density distribution of an electron?
I am wondering if the mass density profile $\rho(\vec{r})$ has been characterized for atomic particles such as quarks and electrons. I am currently taking an intro class in quantum mechanics, and I ...
4
votes
1answer
618 views
Particle physics getting started
I know classical physics, quantum mechanics, special relativity, basic nuclear physics.
I would like to get into some particle physics.
I want to get into that higgs boson, lepton, quark things :D
...
3
votes
2answers
282 views
More on matter and anti-matter
1.) Does every particle that has rest mass also have an anti-particle with which it would annihilate?
2.) Does annihilation only occur between like particles? For example what happens if a ...
1
vote
1answer
184 views
What are the average matter, antimatter, and binding energy composition of protons and neutrons?
For a free baryon at rest at room temperature, how much of its ~1Gev (rest) mass can (on average) be considered as matter, as antimatter, and as binding energy?
For a baryon in a nucleus, I assume ...
32
votes
5answers
2k views
Why do we think there are only three generations of fundamental particles?
In the standard model of particle physics, there are three generations of quarks (up/down, strange/charm, and top/bottom), along with three generations of leptons (electron, muon, and tau). All of ...
16
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4answers
1k views
What is your simplest explanation of the string theory?
How would you explain string theory to non physicists such as myself? I'm specially interested on how plausible is it and what is needed to successfully prove it?
7
votes
3answers
606 views
What actually happens when an anti-matter projectile collides with matter?
I'm trying to understand what would really happen when large quantities (e.g., 10g) of anti-matter collide with matter. The normal response is that they'd annihilate each other and generate an ...
16
votes
3answers
714 views
How do we know Dark Matter isn't simply Neutrinos?
What evidence is there that dark matter isn't one of the known types of neutrinos?
If it were, how would this be measurable?
10
votes
7answers
2k views
Why do neutrons repel each other?
I can understand why 2 protons will repel each other, because they're both positive. But there isn't a neutral charge is there? So why do neutrons repel (do they even or Have I been misinformed?)
...
7
votes
3answers
843 views
Does a particle annihilate only with its antiparticle? If yes, why?
Or to put the question another way - what is the result of a proton-positron collision, or an up quark-charm antiquark collision, etc.? As far as I know, annihilation happens only between particles of ...
5
votes
1answer
350 views
Is there a concise-but-thorough statement of the Standard Model?
I’m a grad student in high-energy physics. I’m familiar enough with the Standard Model, but I’ve always wondered whether there existed a canonical statement of, effectively, “what we talk about when ...
4
votes
2answers
425 views
Can black holes be created on a miniature scale?
A black hole is so powerful to suck everything into itself. So is it possible that mini black holes can be created? If not then we could have actively disproved the rumors spread during LHC ...
1
vote
1answer
330 views
Is all matter made of virtual particles?
This article in New Scientist says that all matter is actually virtual particles popping in and out of existence and nothing more. is this correct?
9
votes
2answers
705 views
What happens to matter in a standard model with zero Higgs VEV?
Suppose you reset the parameters of the standard model so that the Higgs field average value is zero in the vacuum, what would happen to standard matter?
If the fundamental fermions go from a finite ...
10
votes
4answers
1k views
What are the details around the origin of the string theory?
It is well-known even among the lay public (thanks to popular books) that string theory first arose in the field of strong interactions where certain scattering amplitudes had properties that could be ...
11
votes
1answer
368 views
How to determine the mass of a quark?
As far as I know quarks are never found in isolation, so how can we determine their rest mass?
14
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2answers
1k views
Particle physics plots
I'm having a hard time understanding what some of the plots that are presented by ATLAS/CMS actually show. See for example: http://resonaances.blogspot.com/2011/07/higgs-wont-come-out-of-closet.html
...
8
votes
2answers
990 views
Is it pions or gluons that mediate the strong force between nucleons?
From my recent experience teaching high school students I've found that they are taught that the strong force between nucleons is mediated by virtual-pion exchange, whereas between quarks it's gluons. ...
9
votes
2answers
2k views
How come neutrons in a nucleus don't decay?
I know outside a nucleus, neutrons are unstable and they have half life of about 15 minutes. But when they are together with protons inside the nucleus, they are stable. How does that happen?
I got ...
8
votes
2answers
628 views
How can neutrinos oscillate though the lepton flavors have differing masses?
Since the total mass-energy for the neutrino presumably does not change when a neutrino changes lepton flavor, though the mass is different, what compensates for the gain or loss of mass? Does the ...
5
votes
2answers
686 views
The contribution to mass from the dynamical breaking of chiral symmetry
The claim is often made that the discovery of the Higgs boson will give us information about the origin of mass. However, the bare masses of the up and down quarks are only around 5 MeV, quite a bit ...
3
votes
1answer
650 views
Are There Strings that aren't Chew-ish?
String theory is made from Chew-ish strings, strings which follow Geoffrey Chew's S-matrix principle. These strings have the property that all their scattering is via string exchange, so that the ...
9
votes
5answers
647 views
6
votes
3answers
257 views
References on the non-compositeness of the known elementary particles
What paper(s) or theory(s) describe or prove that the elementary particles that we have determined today cannot be made up of smaller more fundamental particles?
3
votes
1answer
216 views
What is “charge discreteness”?
I assume it is some kind of quantity. Google only made things more confusing.
I get that it has something to do with circuits.
I also get what a discrete charge is. In fact, I thought charges ...
1
vote
2answers
138 views
Why are atoms particles?
The Oxford English Dictionary definition of particle is as follows:
"A component of the physical world smaller than the atom."
I read an article in NewScientist and it said
"...all particles from ...
9
votes
7answers
1k views
What would happen if you put your hand in front of the 7 TeV beam at LHC?
Some speculation here:
http://www.youtube.com/watch?v=_NMqPT6oKJ8
Is there a possibility it would pass 'undetected' through your hand, or is it certain death?
Can you conclude it to be vital, or ...
4
votes
1answer
84 views
Where can I get the most accurate measurements of parton distribution functions?
Where would I look to get the most accurate experimental values of parton distribution functions for the proton? I know these functions aren't measured directly, but I'd basically like to find a fit ...
13
votes
7answers
2k views
Applications of Algebraic Topology to physics
I have always wondered about applications of Algebraic Topology to Physics, seeing as am I studying algebraic topology and physics is cool and pretty. My initial thoughts would be that since most ...
16
votes
7answers
2k views
Is mass quantized?
I learned today in class that photons and light are quantized. I also remember that electric charge is quantized as well. I was thinking about these implications, and I was wondering if mass was ...
8
votes
2answers
495 views
How are Monte Carlo simulations used in experimental high energy physics?
How are Monte Carlo simulations used in experimental high energy physics? Particularly in studying detectors limitations (efficiencies?) and data analysis.
I will appreciate giving a simple example ...
6
votes
2answers
1k views
What is the definition of colour (the quantum state)?
I heard somewhere that quarks have a property called 'colour' - what does this mean?
12
votes
2answers
376 views
Why is the (free) neutron lifetime so long?
A neutron outside the nucleus lives for about 15 minutes and decays mainly through weak decays (beta decay). Many other weakly decaying particles decay with lifetimes between $10^{-10}$ and $10^{-12}$ ...
9
votes
2answers
3k views
What's the difference between inclusive and exclusive decays?
For example, why is the semileptonic $B$ decay $B \to X\ell\nu$ inclusive?
I can't find any definition of these frequently used terms, strange.
5
votes
2answers
412 views
What is the fastest process or shortest time in nature?
We know about some events that happen very quickly. For example, the dielectric relaxation time is about $10^{-14}\, \mathrm{seconds}$.
I'm interested in other processes that switch extremely fast ...
3
votes
0answers
308 views
Isn't a single Quantum one single string? [duplicate]
In physics, a quantum (plural: quanta) is the minimum amount of any physical entity involved in an interaction.
In Quantum Mechanics There is no difference between one Quantum to another one.
...
3
votes
2answers
272 views
Is there any idea why the electric charges of electron and muon are equal?
Is there any idea explaining why the electric charges of electron and muon are equal?
Edit:
The total charge of a particle is proportional to the integral of its own electric field flow through the ...
