proton

Quite true!

What is it that you are claiming that is demonstrably false.? Not true. Also not true. I was referring to your comment You misunderstood the point I was trying to make. I wasn’t disagreeing with you. All I was saying was that the reason why the scale can’t tell the difference is because general relativity holds that the two are identical in value and in nature. Let me start from scratch for the sake of clarity. Let us start with a definition of weight from a GR point of view. For this reason I will use the terms as defined in the following article The equivalence principle and the question of weight, Kenneth Nordtvedt Jr., Am. J. Phys. 43(3), March 1975 You've probably seen weight defined differently in basic physics texts as being identical to gravitational force. Those texts usually define the term without considerations from general relativity in mind. This is not the best way to define weight. Not all authors define it that way though. One notable example is A.P. French in his text Newtonian Mechanics. French actually wrote up a nice article in AJP on why this was a better way to define weight. The article is On weightlessness, A.P. French, Am. J. Phys. 63 105 (1995). Randall Knight changed the way he defines weight in his basic physics text to be consistent with the definition above. The equivalence principle can be stated as the gravitational forces are identical in nature to inertial forces. Therefore the equivalence principle it is impossible to distinguish whether the scale is measuring inertial weight or gravitational weight. Thank you for your personal opinion on whether the gravitational force is "real" or not. However I don't see how the classification of the gravitational force as being an "apparent" force or a "real" force effects how we make measurements and what the results of those measurements are. I try to stay away from arguements about semantical things like this so I'll state my personal opinion on this point and leave it at that (I hate semantics). What you said is not quite right and it is most certainly not universally accepted. There are two different opinions on this point. One is the position that since the gravitational force is real and since they are identical in nature to inertial forces then inertial forces are also real. The other position is that inertial forces are pseudo-forces and since gravitational forces are identical in nature to inertial forces it follows that gravitational forces are also pseudo-forces. An example of the former can be found in the highly praised text The Variational Principles of Mechanics, by Cornelius Lanczos as well as French’s text mentioned above. Lanczos writes on page 98 And it was Einstein who held that the gravitational force is “real” and for that reason also held that the Coriolis force was also “real.” Have you ever read the book Theory of Relativity, by Wolfgang Pauli? The author notes this very thing on page 148 I don’t understand what you mean by this!? Are you saying that weight can’t be measured? I disagree. There is no reason why gravitational force can’t be measured. Why would you say otherwise? Just because GR holds that gravitational forces are inertial forces it doesn’t mean that they can’t be measured. That is quite inaccurate. A scale works by requiring the body placed on the scale to be in mechanical equilibrium. This means that the contact force between scale and object must have the same magnitude but opposite direction as the gravitational force.

General relativity holds that the two are identical.

cperkinson - What you've attempted to describe above is quite similar to something called the multiverse. Of course you have a misunderstanding about the Big Bang regarding the "little atom blowing up." The term "Big Bang theory" is an unfortunate term since it makes it sound like the theory addresses an event when the universe started to expand. It also makes it sound like something exploded. No such event is contained in the Big Bang theory as it now stands. Peebles explains this in his cosmology text as follows However the basic idea you have been trying to get at has been around for a very long time. You can read about it at http://en.wikipedia.org/wiki/Multiverse The resistance you've received in this thread so far is a result of the fact that you have not provided any reason to believe that such universes actually exist. Having a theory is useless unless you can provide a reason why it should be considered. Mere belief will get you nowhere in science.

Nah! Since you meant "rest mass" your statement was basically correct. I used the term "basically" because I assume you had something very specific in mind when you said it, e.g. that the proper mass of a photon is zero. There are instances where one could say that "light" (as in multiple photons) has non-zero rest mass. For example: when a physicist says that light has zero “rest mass” they are referring to the fact that since the energy of light is related to its momentum by the expression E = pc the norm of the photon's 4-momentum equal to zero. However if you had an ideal gas of photons, e.g. the cosmic microwave background radiation, then it can be said that proper mass density of such a gas is non-zero. If the amount of photons was finite and one were to integrate over all the photons then the proper mass of such a system is non-zero. This comes from the fact that for such a gas there is a frame of reference in which the momentum density of the radiation is zero but the energy density is non-zero. I know of at least one place that this is done in the physics literature, i.e. in Gravitation and Spacetime - Second Edition, by Ohanian and Ruffini, W.W. Norton & Company, (1994), pages 587 and 589. This is the chapter on the early universe. At that epoch the universe was said to be radiation dominated. For example: if you have two photons which have the same energy, E, but are moving in opposite directions then the total momentum of the two photon system is zero. The proper mass of the two photon system (also known as the invariant mass) is not zero but has the value m = 2E/c2 Regarding the two definitions of the term "mass". A similar problem (i.e. the overloading of the term "mass") exists with the term "lifetime." When a particle physicist says that the lifetime of a free neutron is 15 minutes he is referring to the proper lifetime[/b], i.e. the lifetime as measured from a frame of reference in which the neutron is at rest. Some relativists use the term "lifetime" to refer to the lifetime of the neutron as measured from a particular frame of reference. As defined this way the lifetime is a function of the speed of the particle. So if a person were to say that the lifetime of a neutron is independent of the particle's speed then to determine whether or not he is correct one must determine what the person means by the term. I had cperkinson in mind when I wrote that. . My apologies if there was any confusion over this.

If m is proper mass then the precise expression is [math]E_0= mc^{2}[/math] People all too often forget the "0" subscript denoting proper energy. Merged post follows: Consecutive posts merged Not if you post in English. Words like "theory" have very specific meanings. Just because you come up with a thought and then choose to call it a theory doesn't mean that the term "theory" as defined, say, in the dictionary, will be consistent with the way you've used it. I can tape two screwdrivers together and call it a plunger. But that doesn't mean a plumber can use it to unclog a drain. Merged post follows: Consecutive posts merged In General Relativity (GR) the uniform gravitational field is very tricky. People have the tendancy to use Newtonian thinking without realizing it. In Newtonian mechanics a uniform gravitational field has (1) the same gravitational acceleration throughout the field and (2) a vanishing tidal force tensor. In GR this is no longer the case. In GR a uniform gravitational field has zero spacetime curvature (i.e. no tidal forces present). However in such a spacetime the the gravitational field strength varies with height in the field. The change is extremely small but present.

The questions posed above are best answered utilizing the charge/water analogy. Picture a garden hose whose ends are joined so as to make a closed loop. The water represent charge. Let the hose be completely filled with water. Current is then analogous to the water moving through the hose. When the water begins to flow there is no gap in the hose due to a lack of water. When water leaves one point it only does so when water from a previous section occupies the space being vacated by the water leaving it.

For example: Let two electrons be moving head on where one electron has spin up and the other electron has spin down. After they collide it will be impossible, if not meaningless, to determine/say which electron was which. The total angular momentum must be conserved. That means that whatever spin is measured on one of them the other must have the exact opposite. Ouch!! Personally I'd never put it in those words. I'd phrase it as the system is in a superposition of two eigenstates.

If someone didn't assume you were talking about a hypersphere it in no way means that they are not smart. For example; I myself initially thought you were referring to a three-dimensional object moving in a 4-dimensional space. How does that make me a not smart enough (for whatever we're supposed to me smart enough for)?

You must be referring to rest mass. However, since light has energy it also has mass according to E = mc2. Note that in this context the m in this expression is not rest mass. E is therefore not rest energy but total energy. For a photon all its energy is kinetic energy so that the mass of the photon is all from its kinetic energy. Note: Some people refer to this m = E/c2 as relativistic mass. Other people refer to it as inertial mass. If you disagree with what someone is saying you really should provide a reason for it and not just disagree. Merely disagreeing is of no use to anyone except to convey the fact that you disagree. A solid arguement contains reasons. For example; cperkinson should have explained what he thinks light is, how it is different in nature to an electromagnetic waves, where he got such an idea, and any proof of it that he may know of.

It's clear from this response that cperkinson doesn't understand what light is. cperkinson - Light is an electromagnetic wave. A radio wave is also an electromagentic wave. The only difference between light and a radio wave is the frequency. This is not something that is disputed in physics. This is accepted as a well known fact and has been born out in the laboratory. This was proved by James Clerk Maxwell a very long time ago. To this point Maxwell wrote Why would you think otherwise?

Photons do effect/interact with charges via the Compton Effect. See http://en.wikipedia.org/wiki/Compton_scattering. It would be odd if they didn't. In a certain sense one can think of EM waves as being composed of photons and EM waves effect charges.

I don't see how but I am aware of some journal articles that seem to think that question is still open. For example Can EPR-correlations be used for the transmission of superluminal signals? P. Mittelstaedt, Ann. Phys (Leipzig) 7 (1998), 7-8, 710-715

I'm not quite sure what you mean by "exhibit a quantum effect" but I can tell you that the wavefunction is related to position measurements of a point particle. However macroscopic objects can't be considered to be point objects. So if the uncertainty in position is larger than the dimensions of the body I'd say that the the de Broglie hypothesis won't apply.

I assume that you're more interested in the detection of photons and the collapse of the state rather than how the eye works so I'll refer to detection of photons in what follows. If you're wondering about the eye and how it detects photons please see http://math.ucr.edu/home/baez/physics/Quantum/see_a_photon.html Yes. The wave-particle duality and the principle of superposition are closely tied. You can't address one without addressing the other. The wave nature of light refers to the wave function that corresponds to the probability density corresponding to position measurements. If the wave function is that of a wave packet then it is the superposition of an infinite number of waves. When the photon is detected then its position is measured. This means that the wave function collapses into an eigenstate of position. The further away from the source the detector is the smaller the amplitude of the wavefunction. This translates into a decrease in light intensity and thus a decrease in the probability of detecting a photon in a particular region of space. Is that close to what you were looking for?

The twin paradox doesn't actually need to be solved. The reason it's called a paradox is because it defies intuition, i.e. it is merely an apparent contradiction. It's not really something that is not understood by relativists. In fact it's one of those things that's understood very well.

Each particle has an anti-particle associated with it. The anti-particle has the same mass as the particle but the opposite charge and opposite magnetic moment of the particle. When matter and anti-matter annihilate the result is a two or more photons.

I disagree. The intensity of light is not proportional to the amplitude but to the square of the amplitude.

I don't understand what you've written. What are x and y. And why do you asser that "In two dimensions this is the normal dot product of r and v"? I.e. where did this relationship come from?

Science is about describing nature. It’s circular to say that science “explains” anything (although we often word it as if it does). The typical application of the scientific method starts out with observations, lots of them. From those observations scientists attempt to formulate an hypothesis which describes what was observed. The formulation comes in the form of a "law" (postulate, axiom etc) which attempts to describe the observations. The laws almost always come with the power to make predictions. To be precise one should say Science does not explain; it only describes. Fritz Rohrlich covers this topic his new text Classical Charged Particles in the first chapter which is entitled Philosophy and Logic of Physical Theory. For example, on page 2 the author writes

In the comments above it was said that photons don’t have mass. What was meant by that is it has zero proper mass (aka rest mass) . However light does have inertial mass, since it carries momentum, it has passive gravitational mass, since it is acted on by gravity, and it has active gravitational mass, since it generates a gravitational field. Feyman comments on this in the Feynman Lectures Vol on page 7-11. In the section entitled Gravitation and Relativity Feynman wrote Here Feynman is referring to the passive gravitational mass of light. Re – Because photons follow the curved space-time created by earth's gravity. Light is deflected in a gravitational field, not because of spacetime curvature, but due to the gravitational field it generates. Spacetime curvature is not a necessary condition for the deflection of light in a gravitational field. For example; if light is moving in a uniform gravitational field then it will be deflected even though there is no spacetime curvature in such a field. Re – Does light have mass? That depends on what one means by the term “mass”. A photon has non-zero inertial mass, passive gravitational mass and active gravitational mass. However it has zero proper mass.

In Newtonian gravity Possion's equation is the trace of the tidal force tensor set proportional to the mass density. Therefore a zero tidal force tensor gives zero mass density. If there is a cavity centered at the point then the tidal force tensor may or may not be it zero there. In the present case of, say, a spherical cavity at the center of the earth then it will be zero. Otherwise it will depend on the shape of the cavity. If the center of a spherical cavity is not at r = 0 and the earth is a sphere of uniform mass density then the tidal forces in the cavity will be zero since the field is uniform in such a cavity. A square cavity will give different results of course.

Ant virtual particle can travel faster than the speed of light so they wouldn't be the first particles to be tachyon-like. However tachyons are real particles, not virtual particles. Kyrisch - I believe illinglsu is right. See http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/black_gravity.html Merged post follows: Consecutive posts merged Correctiob; He may be right.

The gravitational field is zero at r = 0 but the tidal force tensor is non-zero. In this instance there is a difference between no gravitational field and the field vanishing at the point r = 0. In GR lingo one would say that the gravitational field (Christofel symbols) vanishes at r = 0 but that the spacetime curvature does not vanish there.