For questions about probability, probability theory, probability distributions, probability density matrix, expected values and related matters. Purely mathematical questions should be asked on Math.SE.
Questions tagged [probability]
1477 questions
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If I sliced the universe in half, would the slice go through a star?
This question is based on a discussion with a 10-year old. So if it is not clear how to interpret certain details, imagine how a 10-year old would interpret them.
This 10-year old does not know about relativistic issues, so assume that we are living…
user78574
93
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8 answers
Why is the application of probability in Quantum Mechanics fundamentally different from application of probability in other areas?
Why is the application of probability in Quantum Mechanics (QM) fundamentally different from its application in other areas? QM applies probability according to the same probability axioms as in other areas of physics, engineering, etc.
Why is there…
Nikos M.
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Can 1 kilogram of radioactive material with half life of 5 years just decay in the next minute?
I wondered this since my teacher told us about half life of radioactive materials back in school. It seems intuitive to me to think this way, but I wonder if there's a deeper explanation which proves me wrong.
When many atoms are involved, half life…
uylmz
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Why is radioactive half-life constant?
Say you have just four radioactive atoms with a half-life of one hour. (I am using a small number of atoms to keep it simple and illustrate my confusion more clearly). So that means one hour from now, two of the atoms will have decayed (on average)…
Luke B
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How close does a particle-antiparticle pair need to be for annihilation to happen?
I've most often seen the statement that the annihilation of a particle and its antiparticle occurs when they 'collide' with one another. So in other words when they get very close to one another right?
How close do they need to be (for annihilation…
docscience
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37
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6 answers
Why doesn't the nucleus have "nucleus-probability cloud"?
While deriving the wave function why don't we take into the account of the probability density of the nucleus? My intuition says that the nucleus is also composed of subatomic particles so it will also have probability cloud like electrons have. Do…
Tim Crosby
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What is the probability for an electron of an atom on Earth to lie outside the galaxy?
In this youtube video it is claimed that electrons orbit their atom's nucleus not in well-known fixed orbits, but within "clouds of probability", i.e., spaces around the nucleus where they can lie with a probability of 95%, called "orbitals".
It is…
Klangen
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Why do all the atoms of a radioactive substance not decay at the same time?
Why does the substance decay at a rate which is proportional to the amount of the substance at that moment?
As all atoms are in hurry to become a stable atom and as their decay do not depend on any external things (like pressure, decaying of…
Sanjib Ray
- 409
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What is a wave function in simple language?
In my textbook it is given that
'The wave function describes the position and state of the electron and its square gives the probability density of electrons.'
Can someone give me a very simple example of a wave function with explanation?…
Mriganka Parasar
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How does QFT predict the probability density to find a particle at x?
In quantum mechanics, the probability density of a particle's position is $$\rho(x)=|\langle x|\psi\rangle|^2$$
What is the corresponding expression in QFT to predict this distribution? Since $\rho(x)$ can be measured (at least to some accuracy) in…
spinachflakes
- 7,318
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4 answers
Is the probability of an electron being somewhere zero?
So recently I've been reading "How to teach Quantum Mechanics to your Dog" by Chad Orzel. In chapter 3, he says, if I understood this right, that electrons can only exist in specific quanta - that is they can only be in certain regions, and will…
TheGodlyBeast
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7 answers
Why was quantum mechanics regarded as a non-deterministic theory?
It seems to be a wide impression that quantum mechanics is not deterministic, e.g. the world is quantum-mechanical and not deterministic.
I have a basic question about quantum mechanics itself. A quantum-mechanical object is completely…
user26143
- 6,571
25
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5 answers
Why do coherent states have Poisson number distribution?
In quantum mechanics, a coherent state of a quantum harmonic oscillator (QHO) is an eigenstate of the lowering operator. Expanding in the number basis, we find that the number of photons in a coherent state follows a Poisson distribution.
Is there…
knzhou
- 107,105
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5 answers
Connections and applications of SLE in physics
In probability theory, the Schramm–Loewner evolution, also known as stochastic Loewner evolution or SLE, is a conformally invariant stochastic process. It is a family of random planar curves that are generated by solving Loewner's differential…
Gil Kalai
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Why is a Hermitian operator a "quantum random variable"?
To me, as a stupid mathematician, a random variable is a measurable function from some probability space $(\Omega, \sigma, \mu)$ to $(\Bbb{R}, B(\Bbb{R}))$. This makes sense. You have outcomes, events, and probabilities of these events. A random…
user79317