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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 ...


10

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} ...


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 ...


6

OK, I found a recent link: Planck versus BICEP2 Despite the new data, the collaboration did not give any insights into the recent controversy surrounding the possible detection of primordial "B-mode" polarization of the CMB by astronomers working on the BICEP2 telescope. If verified, the BICEP2 observation would be "smoking-gun" evidence for the rapid ...


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 ...


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

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 ...


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 ...


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 ...


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 ...


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 ...


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 ...


1

You can easily find the answer in Wikipedia, http://en.wikipedia.org/wiki/Positron_emission. One source of positrons are nuclear reactions. I just quote from there: "In 1934 Frédéric and Irène Joliot-Curie bombarded Aluminium with alpha particles to effect the nuclear reaction $$\ _2^4He + _{13}^{27}Al \to _{15}^{30}P + _0^1n,$$ and observed that the ...


1

There are basically three methods: Bombardment, decay, decay following bombardment. But really all positron emitters that exist on earth in practical quantities are man made: it always starts with bombardment of nuclei with protons, deuterons or alpha particles. Usually the "thing" that is made is the unstable nucleus - the actual production of the ...


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

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, ...


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...


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 ...


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. ...



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