# Tagged Questions

The result of sampling the property of a system

1answer
104 views

### Uncertainty in the average of a series of photon counting measurements

I'm a bit stuck on a problem relating to statistics in photon counting. I'm measuring a spectra with a spectrometer and can set a measurement time and number of times to repeat the measurement in ...
3answers
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### Has the speed of gravity been measured experimentally? How? [duplicate]

In Newtonian physics, changes in gravity propagate instantly. In general and special relativity, gravity propagates at the speed of light, $c$. From reading answers to questions about gravity on this ...
2answers
140 views

### Does infinite actually occurs?

I tend to deny any claim that $X$ is infinite, where $X$ is anything from our observable universe. For instance: The number of grains of sand on Earth is infinite? No, it is a big number but not ...
1answer
65 views

### Do we regularly measure and update our physical constants (By using the LHC)?

This question is motivated by sheer curiosity. I certainly do not expect that the free parameters we use in the standard model have changed in value since we started measuring them with a "modern" ...
2answers
121 views

### Why is a silicon ball with an exact number of atoms a bad measure of mass?

I have some friends that are talking about why a silicon ball with an exact number of atoms is a good/bad measurement of mass (1kg) and things are getting pretty exotic. Is there a layman's ...
1answer
71 views

### Are measurements of time and distance independent or always coupled by the speed of light

In texts about special relativity the light clock is usually described as a tool to measure time $t$. It counts how often light travels along a given distance $d$, i.e. $t = d/c$, where $c$ is the ...
1answer
302 views

### How can the orbit of Jupiter's moons be used to calculate the speed of light? [duplicate]

How can the orbit of Jupiter's moons be used to calculate the speed of light? It seems this was one of the first methods and goes back to 1656.
4answers
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### How does one describe a state with a density matrix after measuring position?

My question is about position measurement in non relativistic quantum mechanics. I've been taught that when you measure the value of an observable for some state of a system described by $|\psi\rangle$...
1answer
57 views

### How might we measure the size of a proton? (Without high energy collisions) [closed]

What methods could we use to measure the diameter of sub-atomic particles. Please think of something inventive, like an indirect technique. Or name some of the lesser known techniques that have been ...
0answers
137 views

### What are the longest half-lives we can detect experimentally? What stops us going further? Are we trying to?

Xenon 136, apparently, has a half-life of 2.11×1021 years. This strikes me as a humongously long time to run an experiment, clocking in at about 11 orders of magnitude longer than the age of the ...
2answers
142 views

### Simultaneous measurement for quantum entanglement

In the simple example that we measure the spin of two entangled particles, we measure one to have spin up so we know the other has spin down. If we could (theoretically) measure both particles at the ...
1answer
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### How do we measure mass?

How do you measure mass? Weight is easy using a scale, but we can't measure mass that way, because then mass would be different on every planet. I know there was a Veritasium video (here) on defining ...