This question came about from a side discussion that arose on this: Does GR provide a maximum electric field limit?

Can we change our choice of coordinate system completely independent of physical motion, and still refer to coordinate dependent components as observations? For example if we have an inertial coordinate system in which we measure the electric field to be E, and now I want to boost the coordinate system to a different inertial coordinate system and state what the electric field E' is in this new coordinate system, do I need to physically accelerate to justify this change in coordinate system (and therefore need to worry about effect such as Unruh, etc. during "changing" the coordinate system)?

I would like to know about the larger picture, current state and future prospects of the sequence of papers that were written by Sheldon Katz and Cumrun Vafa on F-theory. (Freddy Cachazo was also a co-author in many of these papers)

I guess the same is also known as "geometric engineering". (Kindly explain if that is not the same)

There have been recent works on F-theory by Cumrum Vafa, Jonathan Heckman and others.

I would like to know of how this recent work fits in with the earlier work by Katz and Vafa and where do people see this pursuit to be going and what does the community think of its future prospects.

Are these Katz-Vafa works a prospective field for beginning grad students?

I don't really know anything about physics even though I pretended studying it for years.

How is this explained?: http://andrewsullivan.theatlantic.com/the_daily_dish/2011/01/if-you-think-youre-cold-.html

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What is there to be said about it?

My apologies if you find the question too vague or silly.

1. A mass of m = 6 kg has been accelerated by three separate forces acting in different directions in 2-dimensional space. Let each force be given by its acceleration vector in polar coordinates (R, q):

a₁ = 10 m/s² at an angle of 45^o

a₂ = 15 m/s² at an angle of 130^o

a₃ = 4 m/s² at an angle of 320^o

1. Find the magnitude of the resultant acceleration and the direction at which it is pointing.
2. What is the resultant magnitude of the force on the mass m?

A solid sphere of radius 40.0 cm has a total positive charge of 44.4

A jogger travels a route that has two parts. The first is a displacement of 2.90 km due south, and the second involves a displacement that points due east. The resultant displacement + has a magnitude of 3.90 km. (a) What is the magnitude of , and (b) what is the direction of + as a positive angle relative to due south? Suppose that - had a magnitude of 3.90 km. (c) What then would be the magnitude of , and (d) what is the direction of - relative to due south?

A submarine can use sonar (sound traveling through water) to determine its distance from other objects. The time between the emission of a sound pulse (a "ping") and the detection of its echo can be used to determine such distances. Alternatively, by measuring the time between successive echo receptions of a regularly timed set of pings, the submarine's speed may be determined by comparing the time between pings. Assume you are the sonar operator in a submarine traveling at a constant velocity underwater. Your boat is in the eastern Mediterranean Sea, where the speed of sound is known to be 1522 m/s. If you sent out pings every 4.1 s, and your apparatus receives echoes reflected from an undersea cliff every 4.09 s, how fast is your submarine approaching the cliff?

Why is it important to have energy conversion efficiency in our lives and our world?

What total energy is stored in the capacitors in the figure below

(C₁ = 0.643

Two capacitor plates are equally and oppositely charged. They are separated by 1.5cm . 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.

Scientists use the scientific method to
A.   Define new theories.
B.   Make hypotheses.
C.   Set up experiments.
D.   Gain new scientific knowledge.
  
   

Science has existed since
A.   The beginning of human history.
B.   The time of Galileo.
C.   The time of the ancient Greeks.
D.   The time of Newton.
   

A scientific hypothesis is
A.   An educated guess.
B.   A well-established set of results that has been tested over and over by experiments.
C.   A random set of assumptions scientists make before starting an experiment.
D.     An educated guess that tentatively answers a question or solves a problem in the physical world which can be tested by experimentation.
   

What is the difference between a law and a theory?
A    A law is a natural phenomenon about which competent observers can agree; a theory is a general statement about the relationship of natural quantities that has been tested over and over again and has not been contradicted.
B    A law is the synthesis of a large body of information that encompasses well-tested hypotheses about certain aspects of the natural world; a theory is a general hypothesis that has been tested over and over again and has not been contradicted.
C    A law is a general hypothesis that has been tested over and over again and has not been contradicted; a theory is the synthesis of a large body of information that encompasses well-tested hypotheses about certain aspects of the natural world.
D    A law is the synthesis of a large body of information that encompasses well-tested hypotheses about certain aspects of the natural world; a theory is an educated guess which can be tested by experiment.

Science and technology are
A   The foundation of all modern economic success.
B   Share no common traits whatsoever.
C   The same thing.
D   Related to one another in that technology allows humans to apply the organized knowledge of science for practical purposes and provides the instruments scientists need to conduct their investigations.
  

Science and technology are
   
A.      The foundation of all modern economic success.
B.      Share no common traits whatsoever.
C.      The same thing.
D.      Related to one another in that technology allows humans to apply the organized knowledge of science for practical purposes and provides the instruments scientists need to conduct their investigations.
Science, art and religion do not contradict one another because
   
A.       Only science matters, not religion or art.
B.       All three have different domains, and seek to answer different questions about the world.
C.       Only art matters, not religion or science.
D.       If you focus on one of the three, you can disregard the other two.

In science, facts
   
A.       May change over time.
B.       Are irrelevant.
C.       Are absolute.
D.       Are the result of theories.

Pseudoscience can be described as
   
A.      A theory or practice that purports to use the methods of science but actually has no scientific foundation.
B.      The study of physics, chemistry, earth science, and astronomy, and their relationship to one another.
C.      Science on a small scale.
D.      The science of mythical creatures.      

I was reading the Feynman lectures in physics and after thinking about it for a while it seems particularly unreasonable to talk about hidden variables. Let us say that the electron has some internal variables as yet unknown which determine its trajectory given a set of initial conditions just like in classical mechanics. But since these hidden variables are unobserved, coupling it with a classical system should make their effect unchanged. This is what Feynman says, I think, in the last paragraph of Ch1 Vol 3, that if in the double slit experiment, if these inner variables dictate that the electron goes through the upper slit and land at a particular place on the opposite screen, and some other place for the lower screen, then the probability must neccesarily be the sum of two Gaussian like peaks, which does not agree with experiment.

So if I concluded that inner workings of an electron had some additional hidden variables, then it should yield, as they should be independent of the classical apparatus, mutually exclusive probabilities that do not quiet add up the way as observed. But then I do a hidden variables search on the archive and a lot of smart guys still write about it, as late as Feb 2011.

So the argument I have used might be somehow incomplete, can anyone explain how?

EDIT: Sorry for editing this question almost three years later. I tried to locate the exact reference from the Feynman lectures I was referring to and this is the updated source, Sec 7 Ch 1 Vol 3

We make now a few remarks on a suggestion that has sometimes been made to try to avoid the description we have given:

According to the reports, the shutdown procedures at all the Fukushima reactors were successful, and all the control rods were fully inserted.

So - if there was a meltdown, would the control rods also melt and blend into the resulting material (corium)? If so, would that have the effect of "diluting" the corium in radioactive terms and stabilising it to some extent? (I guess it would depend on the relative melting points of the fuel and the control rods: if the rods are of boron, the melting point is a lot higher than that of uranium.)

In all the discussions about how the heavy elements in the universe are forged in the guts of stars and especially during a stars death, I usually hear that once the star begins fusing lighter atoms to produce Iron (Fe) that's the end of the star's life and the whole system collapses onto itself and based on how massive the star was initially it has different outcomes like a white dwarf, a neutron star or a black hole.

I have rarely heard a detailed explanation of how the elements heavier than Iron are produced. I would appreciate a convincing explanation of this process.

A high school kicker makes a 34.0yd field goal attempt (in American football) and hits the crossbar at a height of 12.0ft . What is the magnitude of the net displacement of the football from the time it leaves the ground until it hits the crossbar? What is the direction of the net displacement of the football from the time it leaves the ground until it hits the crossbar? Assuming the football took 2.70s to hit the crossbar, what was the magnitude of its average velocity? What was the direction of its average velocity? Explain why you cannot determine its average speed from these data.