IM Egdall

Bart, in your link the author is saying the Michelson Morley (MM) experiments did not show that the speed of light is absolute. The paper is correct. Einstein's light postulate of special relativity says: Light travels at the same speed with respect to all uniformly moving reference frames. OR light travels at the same speed no matter what the speed of the source of that light. But the MM experiments were done in a single reference frame. The light source, the test apparatus, and the detector (film I think) were all at rest with respect to each other (and the Earth.) So MM says nothing one way or another about whether the speed of light is absolute. However, a number of other tests have shown the speed of light is absolute. DeSitter's famous binary star analysis in 1913 was the first one. In 1977, MIT physicist Ken Brecher used a similar technique to verify Einstein's light postulate to one part in a billion.

See http://neutrinoscience.blogspot.com/2011/09/arriving-fashionable-late-for-party.html

I think you mean the expansion of space. Gravity within galaxy clusters overcomes the expansion. As I understand it, things inside galaxy clusters are expanded by the expansion of space, but this expansion has been stopped by the strength of gravity (spacetime curvature). But out there in so-called empty space, there are no galaxies, thus so little gravity that the expansion dominates.

But in general relativity, all particles distort space and time (or spacetime). So in your construct, how do photons, which do not interact with the Higgs field, distort spacetime? In other words, Higg's boson's do not crowd around photons. Yet photons (and allother massless particles) are a source of gravity (distortion of spacetime). So I don't think your interesting idea works.

You are mixing two theories which are not compatible with each other. The standard model refers to quantum mechanics. It includes the Higgs field but says nothing about gravity. Gravity is described in general relativity -- where mass/energy is a source of gravity (which is the warping of space and time or spacetime curvature). New theories like string theory seek to unite quantum mechanics with gravity. But they are still works in progress. So for now we are stuck with 1) quantum mechanics with inherent uncertainty in nature and where the Higgs field gives particles their mass, and 2) general relativity with no uncertainty in nature and where mass/energy produces spacetime curvature. They are two separate and distinct views of the universe.

There is an approach called weak measurements which do "observe them without interfering with them", as you put it. See first article in link: http://physicsworld.com/cws/article/news/48126

As I understand it, if not for the Higgs field, all particles would travel at the speed of light. Most particles, however, do interact with the Higgs, so gain mass (like electrons and quarks). And (I'm not totally sure of this), the faster these particles go, the more they interact with the Higgs field. So they become more and more massive and cannot achieve the speed of light. Some particles (photons, gluons, and the yet to be detected gravitons) do not interact wth the Higgs field, so are massless and travel at the speed of light.

There are a number of matter particles, grouped as quarks and leptons. Quarks form neutrons and protons. Electrons and neutrinos are leptons. Suggest you look at The Particle Adventure. http://www.particlea...-questions.html

It all comes from E=mc^2. Mass and energy are equivalent. They both produce the same physical effects. Such as producing gravity (spacetime curvature). So massless particles such as photons are a source of spacetime curvature -- they distort, bend, warp space and time just like particles with mass do. In addition, photons have momentum and inertia, just like particles with mass do.

An interesting idea, Sorcerer! The big rip at some point becomes so strong it separates out virtual particles from the "vacuum", and they become real particles. But do these new real particles slow down or halt the rip? I donno. And yes, I believe this is similar to the process of inflation, where the exponential expansion of space just after the big bang separated the virtual particles as they popped out of the "vacuum", resulting in the real particles which now make up our universe. (or those that are left after matter-antimatter annihilations -- but that's another story.) I don't think it was this appearance of real particles which slowed inflation, but I may be wrong. Oh, and it is OK for the expansion to go faster than the speed of light. Per Einstein, nothing can go through space faster than the speed of light, but space itself can and does expand faster than the speed of light.

I recommend you read Kenneth Miller's book, Finding Darwin's God. It is a compelling case (overwhelming case actually) for evolution, based on actual evidence. And Miller gives a clever explanation of how his religious beliefs on God fit with the science. Plus Miller explains the evolution of the eye.

The Alain Aspect experiment has been repeated and confirmed a number of times. It is based on Bell's theorum and has to do with Quantum Entanglement. I'll try the latter in simple terms. Consider an atom which simultaneously emits a pair of photons in two different directions. Per Conservation of Angular Momentum, the random polarizations of the two simultaneously emitted photons must be opposite values. Say one photon travels to the left and the other to the right. When they are say 10 feet apart, we decide to measure the polarization of the left-moving photon. Since the polarization of the photons must be opposite, as soon as we measure the left one we immediately know that the right-moving photon (now some 10 feet away) has the opposite polarization value. The key here is that the polarization value of a photon is random. So there is a connection between the random characterstics of the two photons. It would be like flipping a coin in New York and one in LA -- when one shows heads, the other always shows tails. Eisntein, Podolsky, and Rosen (EPR) argued that the polarization of the photons was set as soon as they were emitted by the atom. And all the experiement did was find out what these previously programmed values were. Quantum physicists argued that the attributes of the photon are in limbo, unknown until you do the measurement. John Bell came up with a way to test which is right. Aspect ran Bell's experiment and it showed that the photon's attributes (like polarization) are in limbo, are random, until measured. This is called non-local. The probabilities of the two random attributes are connected (and represented in quantum mechanics by a single probability amplitude (wave) function). For more on this, I suggest you Google "Quantum Entanglement" and "Bell's theorum" and read the various links. Brian Greene's book, The Fabric of the Cosmos, has a nice lay explanation of all this, and the Bohm theory.I recommend you read it.

The Sun is a star. The closer a star is to us, the brighter the star appears to us. In general, its brightness falls off by the square of the distance. So, for instance, a star which is twice as far away as another identical star would be four times less bright. If it was three times further away, it would be nine times less bright. Etc. The Sun is so close to Earth that its light is bright enough to allow us to read a book. Other stars we see are much, much further away -- so way too dim to read a book from. The Sun is about 93 million miles from the Earth. The next nearest star is Proxima Centauri, which is about 4.2 light-years (about 25 trillion miles) from Earth. If my calculations are correct, this is some 270 thousand times further away. Also stars vary tremendously in their size, make-up, and brightness. So this is also a big factor in how bright the star appears to us.

For a beginner's intro to particle physics, I like The Particle Adventure http://www.particleadventure.org/

As Dr. Rocket said, per the modern understanding of quantum mechanics, nature is inherently stochastic (non-deterministic). Fowler's link says the act of measurement disturbs the experiment, thus producing the uncertainty. This is a simplification. Per QM, the uncertainty is already there, inherent in nature itself. This is a subtle but very important point, and a change from what the early thinkers on QM believed. I'm trying to remember the details, but I think Bell's theorum test results support this modern point of view. I also recall some careful experiments where the act of measurement produced such small disturbances that they could not possibly cause the randomness -- yet it was still there in the experimental results.

I love this forum! I especially learn so much from you. You say the stress-energy tensor in Einstein's field equations of general relativity "include ALL non-gravitiational forms of energy." Are you saying the momenergy contained within the stress-energy tensor accounts for energy of motion as well as gravitational energy? What about other forms of energy, like EM fields and strong force fields etc. Are these also included. Please give us other examples if you have them. And a link if you have it for some references that are not too mathematically dense. Thank you. Oh, and I think Baez's initially spherical ball of test particles is in free-fall, not at rest. So wouldn't they change their relationship with respect each other over time? And since Baez is oversimplified, do you know of any other explanation which does not require knowledge of differential geometry which is a better explanation of GR?

Both Newton's theory of gravity and general relativity predict the path of a light beam curves in a gravitational field. For example, starlight grazing the Sun. Newton's model predicts a bending angle of 0.75 arc seconds. Eistein's predicts twice that amount. Observations agree very closely to Einstein's prediction.

Please take a look at recent articles in Scientific American. They give the predictions of climate scientists on global warming/climate change, and show how a number of these predictions are already coming true. (Read my blog on this forum for some examples). More and more doubting scientists have -- after studying the detailed climate record -- changed their minds and come out in support of human-induced global warming. If you want absolute proof, you would have to have two Earths -- one with human activity and one without. Then you would compare the difference human activity makes on our climate over time. Since this is impossible, all we can do is read what the experts are telling us. And they say it is NOT too late. By reducing our output of greenhouse gasses, we can at least slow down if not stop the dire effects predicted by the experts. Again, please read the articles in SciAm or some other reputable journal before you simply argue against this.

Thanks for the clear and excellent explanation.

Who are you going to believe -- a comedian or the overwhelming majority of climate scientists? I'll take the scientists -- who say global warming is real and human-induced climate change is highly likely the biggest contributor. It seems to me we ignore global warming at our own peril -- more severe droughts, more weather extremes, more floods, more intense heat waves, rising ocean waters --all on a global scale. Frankly it scares the hell out of me, and I am so frustrated that so many people fight or ignore what the scientists are telling us. My poor grandchildren --what kind of world will they be facing? Sorry for the rant -- its really a subject for another thread.

E=mc^2 doesn't just apply to nuclear processes like in the core of the Sun or atomic energy (and bombs), it applies to all processes where energy is involved. Say, for example, you have a candle. Then you light the candle and let it burn down. Say you somehow captured all the wax and gases etc. the candle has given off after the candle has burned. Then you compare the weight of the candle before it burned to the weight of all the stuff captured after it burned (very accurately). You find the stuff from the candle afterwards weighs a tiny bit less than the candle before it was lit. Where did this missing mass go? It was converted from mass to energy per E=mc^2 -- that is the missing mass was converted to the energy of the light and heat given off by the burning candle. For other examples, see link: http://www.abc.net.a...ies/3000861.htm

Your description is incomplete. At the risk of sounding like a broken record, let me say again: According to general relativity, the gravitational field IS the warping of space and time or spacetime curvature. A clock runs slower as it gets closer to the Earth's surface. The distance between the same two points stretches as the points approach the surface of the Earth (points perpendicular to the Earth's surface as seen from far away). In Einstein's construct, this warping of time and space is what tells objects how to move in a gravitational field. It is what is holding me down in my chair right now as I write this. So all the physical effects we attribute to the term "gravity" are produced by the warping of space (change in length or space interval) and warping of time (change in time interval). Thus the warping of space and time is gravity. By the way, this change in the space and time intervals is represented mathematically in general relativity by the change in the spacetime interval. The spacetime interval is the square root of the difference between the square of the time interval and the square of the space interval (ignoring cross-terms). I suggest you look up frame dragging and the latest Gravity Probe B results. Here the spinning of the Earth on its axis caused gyroscopes orbiting the Earth to change their spin orientation (very slightly). Why? How can the spinning of the Earth affect the orientation of gyroscopes which are themselves rotating in "empty" space? Because, per general relativity, the spinning of the Earth drags empty space around with it as it rotates. The confirmation of this so-called frame dragging by Gravity Probe B (to about 19%) shows that space IS flexible, is warpable. No matter what we say about how crazy this is -- we now have emprical confirmation of this strangest of phenomena. Link: http://einstein.stanford.edu/highlights/status1.html

Are these forbidden energy values for a given bound system absolute, or are they just the most probable energy values? In other words, can an electron have any energy value in a bound system, but the probability is the highest at the so-called permitted energy values?

I find it easier to think of the warping of distance (or in more formal terms the warping of the space interval). It is the distance between two points which is stretched by the presence of a massive body. Look at the grid analogy. Pick two intersecting points on the grid close to the large object. See the line between them? It is dipping down. This represents that the distance between the two points is now longer due to the presence of the large object. Similarly, two points in space are a certain distance apart. Put a massive object near the two points, and the distance between them (as seen from far away) is greater. This is what general relativity is telling us. (Here the distance I am referring to is a radial distance). So when they say space is warped or curved by the presence of a massive object, it means the distance between the same two points is changed (as seen from far away). And similarly, when they say time is warped or curved by the presence of a massive object, it means the time interval between two events is changed by the presence of the massive object. Together spacetime curvature is the change in the time interval and space interval (distance) between two events due to the presencce of a massive object. (Actually any object produces spacetime curvature -- but it's only significant for massive objects. I hope this helps a little.

Anilkumar - May I suggest the following website as an intro to the use of differential geometry in general relativity. Check it out: http://math.ucr.edu/home/baez/gr/