Suppose you have to specify the moment in time when a given event occurred, a "zero time". The record must be accurate to the minute, and be obtainable even after thousands of years. All the measures of time we currently have are relative to a well defined zero, but the zero is not easy to backtrack exactly.

One possibility would be to take a sample of Carbon with a well defined, very accurate amount of 14C, and say: the event occurred when the 14C was x%. At any time, measuring the rate of decay, you would know when the event occurred. This however, requires a physical entity to measure, which may be lost.

Another way would be to give the time lapsed after a well defined series of solar eclipses. In order to define precisely the context, you would say a list of (say) five consecutive eclipses and the places on Earth where they were total, and then a time gap from the last of the set. At any time in the future, you can backtrack the specified conditions into a celestial mechanics program and find when the event occurred.

Is there a standardized or well recognized method to do so?

I've seen foliation used in the context of "foliation of spacetime" here and elsewhere in papers and such. Generally defined in reference to a "sequence of spatial hypersurfaces." But I don't know what that means either.

Again, I can imagine what these terms mean because of the English language meaning of the words. But what do these mean specifically in reference to the physics of spacetime?

I have read that the fine structure constant may well not be a constant. Now, if this were to be true, what would be the effect of a higher or lower value? (and why?)

Suppose you have to specify the moment in time when a given event occurred, a "zero time". The record must be accurate to the minute, and be obtainable even after thousands of years. All the measures of time we currently have are relative to a well defined zero, but the zero is not easy to backtrack exactly.

One possibility would be to take a sample of Carbon with a well defined, very accurate amount of 14C, and say: the event occurred when the 14C was x%. At any time, measuring the rate of decay, you would know when the event occurred. This however, requires a physical entity to measure, which may be lost.

Another way would be to give the time lapsed after a well defined series of solar eclipses. In order to define precisely the context, you would say a list of (say) five consecutive eclipses and the places on Earth where they were total, and then a time gap from the last of the set. At any time in the future, you can backtrack the specified conditions into a celestial mechanics program and find when the event occurred.

Is there a standardized or well recognized method to do so?

I am sending a couple of questions which seem a bit more specific than others on this site, partially to probe if there is a point in doing so. Not sure what is the range of expertise here, and no way to find out without trying, so here goes:

I am wondering what is known about QCD, or other field theories, in the regime of large density and low temperatures, specifically studied in the large N limit. I know of the qualitative picture at finite N, but lots of the instabilities (e.g. the superconducting ones) are suppressed at large N and replaced by other interesting phenomena. I am only aware at the moment of the DGR instability to form chiral density waves, and I am wondering what else exists in the vast and possibly quite old literature. Any pointers or entry points to that literature will be appreciated

Two capacitor plates are equally and oppositely charged. They are separated by 1.4cm . An electron is released from rest at the surface of the negative plate and, at the same time, a proton is released from rest at the surface of the positive plate.

Where do the electron and proton pass each other? Give your answer as a distance from the positive plate.

The position of a particle is given in cm by x = (8) cos 9?t, where t is in seconds. (a) Find the maximum speed.b) Find the maximum acceleration of the particle.(c) What is the first time that the particle is at x = 0 and moving in the +x direction?

At Enormous State University (ESU), the football team records its plays using vector displacements, with the origin taken to be the position of the ball before the play starts. In a certain pass play, the receiver starts at +1.5 i^ - 3.0 j^, where the units are yards, i^ is to the right, and j^ is downfield. Subsequent displacements of the receiver are +7.5i^ (in motion before the snap), +10 j^ (breaks downfield), ?6.0i^+4.0j^ (zigs), and +12.0i^+18.0j^ (zags). Meanwhile, the quarterback has dropped straight back to a position ?7.0j^.

Part A

How far must the quarterback throw the ball? (Like the coach, you will be well advised to diagram the situation before solving it numerically.)

Express your answer using two significant figures.

Part B

In which direction must the quarterback throw the ball?

Express your answer using two significant figures.

Is Teflon radiodense or radiopaque? Can a CT scan penetrate a thin layer of Teflon?

A diverging lens has a focal length of 18.6 cm .

A. What is the image distance for an object distance of 37.2 cm? Answer with −1000 cm if no image is formed. What is the magnification?

B. What is the image distance for an object distance of 18.6 cm? Answer with −1000 cm if no image is formed. Answer in units of cm. What is the magnification?

C. What is the image distance for an object distance of 9.3 cm? Answer with −1000 cm if no image is formed. Answer in units of cm. What is the magnification?

Calculate the binding energy per nucleon for the following isotopes.

(a) ¹²C
______MeV/nucleon

(b) ¹¹B
________MeV/nucleon

(c) ⁵⁵Mn
________MeV/nucleon

(d) ¹⁹⁵Pt
_______MeV/nucleon

Neutrons from a source (such as beryllium bombarded with particles from radium or plutonium) bombard natural palladium, which is 27% 106Pd. What is the energy output of the reaction 106Pd + n 107Pd + γ? The mass of 106Pd is given in Appendix A, and that of 107Pd is 106.905129 u.

A diverging lens with a focal length of -13 cm is placed 12 cm to the right of a converging lens with a focal length of 21 cm . An object is placed 40 cm to the left of the converging lens. Where will the final image be located?Where will the image be if the diverging lens is 41 cm from the converging lens?

A mass m = 13 kg is pulled along a horizontal floor with NO friction for a distance d =7.4 m. Then the mass is pulled up an incline that makes an angle θ = 32° with the horizontal and has a coefficient of kinetic friction μ_k = 0.31. The entire time the massless rope used to pull the block is pulled parallel to the incline at an angle of θ = 32° (thus on the incline it is parallel to the surface) and has a tension T =59 N.

What is the work done by tension before the block goes up the incline? (On the horizontal surface.)

What is the speed of the block right before it begins to travel up the incline?

What is the work done by friction after the block has traveled a distance x = 4.1 m up the incline? (Where x is measured along the incline.)

What is the work done by gravity after the block has traveled a distance x = 4.1 m up the incline? (Where x is measured along the incline.)

How far up the incline does the block travel before coming to rest? (Measured along the incline.)

On the incline the net work done on the block is:

positive

negative

zero

A crate of mass 9.4 kg is pulled up a rough incline with an initial speed of 1.52 m/s. The pulling force is 110 N parallel to the incline, which makes an angle of 20.8° with the horizontal. The coefficient of kinetic friction is 0.400, and the crate is pulled 4.92 m.

(a) How much work is done by the gravitational force on the crate? J

(b) Determine the increase in internal energy of the crate–incline system owing to friction. J

(c) How much work is done by the 110-N force on the crate? J

(d) What is the change in kinetic energy of the crate? J

(e) What is the speed of the crate after being pulled 4.92 m?

Thank you so much for your help! An explanation of each would be greatly appreciated!!