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8

The most compelling evidence of GR in presence of matter is, in my opinion, in neutron stars. These objects have a surface gravity $SG$ that is (geometric units): $SG_{NS}=GM/c^2 R \simeq 0.1 $ This value is telling us that we can't use Newtonian gravity because we are in the strong field limit. For comparison, the sun has $SG_{SUN}=GM/c^2 R \simeq 10^{-5} ...


0

The field equations of general relativity give rise to a phenomenon called gravitomagnetism, which is related to "monopole" gravity in the same way that magnetism is related to moving electric charges by special relativity. There is conclusive evidence for gravitomagnetism just in the past five years, weakly from the Gravity Probe B mission, and more ...


6

Frame-dragging effects are dependent on the spin of the central object, have been measured by experiments such as Gravity Probe B, and are definitely not dependent on the central metric. Also, any effects on a galactic scale are best quantified in terms of a continuous matter distribution, since the central black hole is a small fraction of the galaxy's ...


1

Chris White's answer covers the content of the question . I will reply to the title At what point do researchers in physics make the leap from wild theoretical ideas to physical experiments? It is very very seldom that wild theoretical ideas lead to physical experiments. And when they do, as with special relativity, which the Michelson Morley ...


2

First, it's important to realize that all proposed changes to physics need to be tested, whether they amount to adding new stuff to the universe or modifying equations that have worked fine thus far. Suppose someone comes along and says, "I can explain this supposed dark matter by modifying gravity," and lots of theorists agree. Great. Now observers will go ...


2

The American Journal of Physics has in its archives a couple hundred "Resource Letters," which are mini-reviews of some interesting topic with several hundred references each. The recent resource letters usually group the references by their complexity, making it easy to find "simple" or "thorough" treatments of a topic. The journal is published by the ...


4

In a way you are right because LIGO hasn't observed anything. But the theory for it working is sound, so you're wrong on that aspect. The light path itself is also affected by the gravitational wave. The Wikipedia article on LIGO says, Note that the effective length change and the resulting phase change are a subtle tidal effect that must be carefully ...


3

Given that you use the tag "home-experiment" I will give an answer in that spirit. Obviously you can use the convex lens to focus the sunlight onto a piece of paper - find the distance where the paper catches fire and that is your focal length. That's how I did it when I was 4. Shoe laces too - they are really stinky when you get the distance right. Wear ...


1

You have to keep in mind that all physical experiments are merely approximations of idealized experiments. No real setup will actually measure a theoretical quantity. They will only measure a reasonable estimate of the quantity, and the measurement will always be marred by statistical and systematic errors. In addition you have to consider sampling errors, ...


3

No such algorithm is known. The natural language description of experimental setups is far too informal to be turned into precise quantum mechanical statements. Therefore, we will in the following suppose that a quantum mechanical description of the measurement apparatus in spe has been provided. In the von Neumann measurement scheme, it is not subjective ...


1

The weighted mean of three values is given by $$ \bar{x} = \frac{ \sum_{i=1}^{3} x_i \alpha_i}{\sum_{i=1}^{3} \alpha_i},$$ where here $\alpha_i$ represents the weight that you give to each measurement. If you wished to just find the weighted mean from your data as you presented it originally, then the weight $\alpha_i = 1/\sigma_i^{2}$. If you then wish to ...


-1

edit - downvoted because i got the $\chi^2$ formula wrong - fixed now....!! The way that I would approach this is to calculate $\chi^2$ with $$\chi^2 = \sum_{i=1}^N\left({p - x_i \over \sigma_i}\right)^2$$ where $p$ is the best value for the fit and $N$ is the number of measurements $x_i$ with error $\sigma_i$. Now with a computer or Excel sheet I would ...


0

I don't know how this is supposed to simulate planetary motion, but we can still look at what data you would expect. The force on the stopper is $\frac {mv^2}r$, which if there is no friction (good luck!) equals the gravitational force on the masses at the bottom. We would therefore expect that for given mass on the bottom, $r \propto v^2$, which doesn't ...


0

Real photons are emitted during accelerations, in synchrotron radiation and bremsstrahlung and it is a classical electrodynamics prediction . The Millikan experiment : Millikan was the first to determine with great accuracy that the maximum kinetic energy of the ejected electrons obey the equation Einstein had proposed in 1905: namely, 1/2mv2=hf−P, ...


2

Spin of an elementary particles is not necessarily the result of a movement of the particle around itself i.e. around some rotation axis that passes through the particle.If there were such an axis, the projection of the spin in the plane perpendicular to that axis were zero. But, this is not the case. So, along whatever axis we would measure the spin, we ...


1

Generally speaking, the choice of what the $z$-axis (equivalently $x,y$) is is arbitrary. You can choose any direction to be your $z$-axis, as long as you do the calculations consistently with this choice. If the system has a priviliged direction (like that imposed by the magnetic field in the Stern-Gerlach case) that is usually choosen to be the $z$-axis. ...


1

If you are measuring in a laboratory with a ruler like the one in your diagram then I would say for a length of $9.5 cm$ you would be able to see with your eye that the length is say $9.5 \pm 0.2 cm$ and if it actually was on one of the markings, e.g. 6, then you might estimate that the measurement was say $6.0 \pm 0.1 cm$. Often when measuring length with ...


0

One of the answers to "How does one produce entanglement?" gives an example of how to obtain pairs of entangled particles. However, it is a complicated example. The simplest procedure, and widely used in experiments, is down-conversion of ultraviolet (UV) photons. Such photons are sent on a type of crystal that we name "non-linear crystal". In short, inside ...


0

That may depend on what you call "invisible". How about a system of direction-sensitive Lytro cameras all around a body and projectors transmitting whatever the cameras on the other side of the body sees in the direction opposite to the sensed one? As of today it's a mildly challenging but doable engineering project. Would such a system count?


-1

It is logically wrong to state that the experiments mentioned in the other answers prove the relativity of simultaneity, since there are alternative theories to special relativity in agreement with all experiments to date in which absolute simultaneity is preserved. In other words no experiment has allowed to observe the relativity of simultaneity. See the ...


15

The interpretation of gravity as curvature of spacetime is model-dependent. You already mentioned the teleparallel equivalent of general relativity, modelling gravity by torsion. Another possibility are bi-metric theories, where the metric is a more ordinary field on a fixed background (this should be more in line with how string theorists tend to think of ...


0

Acceptance is some measure of the fraction of events or the spacial or momentum distributions of events that will be registered in the detector. The exact meaning varies from experiment to experiment and sometimes from analysis to analysis within a single experimental data set. Understanding the acceptance of a experiment for a particular signal can be a ...


9

This is the plum pudding model of the atom Left: Expected results: alpha particles passing through the plum pudding model of the atom undisturbed. Right: Observed results: a small portion of the particles were deflected, indicating a small, concentrated positive charge. There are no electrons and no outer shells, quantum mechanics was yet to come ...


8

The $\alpha$ particle, attracted by the electrons on the outer shell of the pudding, orbits nearly parabolically around the atom, causing the near-180 degree deflection angle seen. This wouldn't happen because of momentum conservation. It was reasonably established in 1909 (when the gold foil experiment was done) that electrons were light, so if an ...


0

Based on thomson's model, all of the alpha particles should go through or reflect back but in Rutherford's experiment, it was more of in between, some reflecting back and some going through, disproving the theory.


1

I have heard of educational innovations.. They have physics lab materials and projects and other interesting science stuff...there is also arbor scientific for high school-like physics projects...


0

Several things spring to mind here. The "brain dead" way to estimate things would be to take the mean of all the samples and divide by the standard deviation. But as you point out, that gives you a rather large standard deviation and it does not take advantage of everything you know. In general, such an approach would suffer very badly from aliasing: if you ...


1

In order to answer your question you must think through the entire measurement. In this case you are measuring the photoelectric effect by placing a photodiode into a circuit. What kind of circuit element is the photodiode? It is a source. And as you have pointed out above, it is a constant voltage source (with voltage determined by the energy of the photons ...


0

In contrast to coordinate time, proper time is independent from any geodesics geometry. Any clock is OK as long as it is in the same frame as the object whose proper time is measured. In order to recover the proper time information, the observer must ensure synchronization of his own clock with the clock of the observed object. Thus, your problem might be ...


0

My point of view in physics is that, given any concept (in this case, proper time), there are always two notions: (1) the theoretical concept defined in the sense of mathematics, and (2) the experimental concept defined in the sense of experiment. We then hypothesize that these two concepts are equal, and of course, if experiment shows that this is wrong ...


1

to solve the problem you need at 4 linear equations (or the two linear ones you have plus another nonlinear one). Otherwise, the solution is undetermined, you have more variables that linear equations and the number of solutions is infinite. Here are the two extra equations that you need. 1) the total force equald the applied force (otherwise it will move ...


3

The uncertainty in any particular measurement is $\sigma_E$. Resolution for these devices is almost always stated in relative terms as here, but take it like this because it depends on the energy measured. So just multiply by the energy. That is, express your signal in $\mathrm{GeV}$ and then find $$ \begin{align} \sigma_E = \left(\frac{0.1}{\sqrt{E}} ...


1

Use a large and thick copper spoon. Put the spoon in the coffee for 3 seconds. Remove it and insert the spoon in your mouth. (beware it will be hot) Use the tongue and palate to cool spoon pushing hard. When the spoon is close to the temperature of your mouth (feels tepid) remove it and reinsert the spoon in the coffee by another 3 secondos plus 0.5 ...


0

well, you could build a faraday cage and go inside it to look at your instruments, no need to transfer information outside - or you could place a recording device inside. if it's a problem for you in your mind that there is a void inside the conductor, that problem would apply on smaller scale as well, your instrument for measuring would still take some ...


0

Writing $\mathcal X_C^{n} := \{ \varepsilon_{ C \mathcal X }^1, ~..., \varepsilon_{ C \mathcal X }^n \}$ for any (variable) suitable ordered subset of $n \ge 1$ events in which $C$ took part, and abbreviating $${\! \large \tilde\tau} C_K^P := \! \! \mathop{ \bf \text{ infimum } }_{ \large {\mathcal X_C^{n} } \subseteq \{ \large{ \varepsilon_{C K}, ~... ~ ...


0

if there is nothing or no one around to hear it Given that trees/forests don't exist in isolation we would have a very difficult time finding a tree that falls with absolutely no creature capable of perceiving sound within a reasonable distance. Go find a forest completely devoid of birds, rodents, snakes, insects, fish etc. Don't forget a 2+km buffer ...


0

Put a microphone & recorder near the falling tree. No one was around to hear the tree fall. Yet you can play the recording and provide evidence of sound.


8

It depends on your definition of "a sound". If a sound is not a sound unless it is perceived as a sound (that is, processed in the auditory system of a sentient being), then the answer is "no". If a sound is a coherent disturbance in the pressure distribution of the air, and this disturbance propagates through the medium "at the speed of sound", then the ...



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