Jump to content

IM Egdall

Senior Members
  • Posts

  • Joined

  • Last visited

Everything posted by IM Egdall

  1. For just the basics of the strong force, take a look at the Particle Adventure http://particleadventure.org/strong.html
  2. A similar kind of time travel happens whenever you change altitude here on Earth. Per general relativity, time runs slower on the surface of the Earth than it does on the top of a mountain (by a very small amount). So if you live at sea-level, when you go to the top of that mountain you arrive there a little bit into the future.
  3. I found this example helped me understand how mass increases with speed per special relativity. Hope it helps you. Astronauts in space are effectively weightless, but they still have mass. They use a contraption called an Inertial Balance Spring Scale to determine if their mass is changing during their time in space. This is a seat set on springs. An astronaut sits on the seat, grabs onto the rails, and pulls him or herself down --compressing the springs. Then the astronaut lets go. The spring scale chair then oscillates up and down as the springs release and compress. The more massive he/she is, the slower the spring scale oscillates. Now imagine a rocket in outer space with a spring scale and astronaut inside. Say the rocket flies by you at 87% the speed of light. Per special relativity, from your point-of-view time inside the rocket goes at half the rate as your time (time dilation). So you see the astronaut on the spring scale oscillating at half the rate than if the rocket were at rest. Since the spring scale oscillates slower by a factor of two, you conclude the astronaut has twice the mass than at rest. This is a relative effect. From the astronaut's point-of-view (reference frame), the uniformly moving rocket is at rest. So his/her mass is unchanged. But to you, the rocket is moving. So you see time on the rocket running at a slower rate and the astronaut's mass as greater. And the greater the rocket's velocity with respect to you, the more you see its time running slower, and the greater the astronaut's mass. The effect is not linear. It goes as the square root (1 - v ^2) where v is the velocity as a percentage of the speed of light. As the rocket's velocity, v approaches the speed of light, its mass approaches infinity.
  4. Another way to look at it is this: Stay-at-home Steve is on Earth. Arianna takes a rocket trip to a distant star and returns to the Earth. When they compare their watches at the end of the trip. they find Arianna's watch on the rocket has run slower than Steve's on Earth. This assymetry is due to the fact that Steve has stayed in a single inertial reference frame all along. But Arianna in the rocket has actually been in two inertial reference frames -- one going away from Earth, and the other returning to Earth. It is this asymmetry experienced by Arianna which results in her clock runnung slower than Steve's. Now you may try to argue that to Arianna, Steve had moved away from the rocket, and then he has moved towards the rocket. But this is not so. Steve felt (measured) no change in speed or direction. (A simple accelerometer would verify this.) But Arianna had to change inertial frames, and in doing so, she did feel (and measure) a change in speed and direction. In the simplest analogy, it is as though Arianna jumped from her outbound uniformly moving ship to an inbound uniformly moving ship. (This is of course a simplification.) Steve did not have to do anything of the sort. He remained in the same reference frame -- the Earth -- the whole time. You can show the slowing of time occurs for the rocket observer and not for the Earth-bound observer using special relativity (time dilation) and the doppler shift. If you want to see the details, go to marksmodernphysics.com then click on ITs Relative, Archives, and The Twins Paradox
  5. It seems to me the disturbance caused by cutting or pushing down on the string will propagate at a speed less than the speed of light. The string is, after all, made up of molecules, and the disturbance to molecules in the center has to be transmitted outward in both directions to adjacent molecules. This takes a finite amount of time which is less than the speed of light. So no contradiction with special relativity.
  6. Per E=mc^2, mass and energy are equivalent. In other words, both mass and energy produce the same physical effects. So both mass and energy produce gravity. And per general relativity, gravity is spacetime curvature (the global warping of space and time by mass/energy). The mass of the Sun, for example, produces spacetime curvature (gravity) in its vicinity. The energy of the Sun (its photons) also produces spacetime curvature (gravity) in its vicinity.
  7. I agree that Hawking's A Brief History of Time is a very good book, but I found few lay people could follow it. My brother-in-law calls it the best seller that nobody read. I also agree that his book The Grand Design was pretty bad. I use Feynman's classic QED, the Strange Theory of Light and Matter in my quantum course for lay students. It is wonderful. I also use Brian Greene's The Elegant Universe and The Fabric of the Cosmos in my courses. I would be interested to know what you think of Greene's popularizations.
  8. Here is my understanding. Yes, according to the big bang theory, it happened everywhere. The "explosion" was the expansion of space itself. But whether the universe is infinite or finite is still unknown. The rule that nothing can travel faster than the speed of light through space is from special relativity. But per general relativity, space itself can (and does) expand faster than the speed of light.
  9. Apparently, CERN has identified two possible issues in their faster than light neutrino results. One, a faulty optical fibre, would make the neutrino speeds less than reported. The other, an oscillator used for GPS timing, wouild make the neutrino speeds greater than reported. I guess we have to wait for further analysis to find out the total impact of these anomolies on the measurements. (The devil is in the details.) See link: http://physicsworld.com/cws/article/news/48763
  10. Well said. I think this agrees with my earlier point. A beam of light across an accelerating elevator will bend. But by half the amount we would see in an equivalent gravitional field. This is because, as you say say, the EP applies only locally. In that sense, the EP is limited (I did not say it was in error). It does not take into account the geometry of space See link: http://www.einstein-online.info/spotlights/equivalence_deflection
  11. Maybe this is not your view, but when I read or hear people make flat-out claims like "global warming is a hoax" or statements like that, I ask "how can you be so definite, so sure in your statement -- is there no uncertainty in this?" What I read (mostly) from the climate scientists are write-ups which include the uncertainties in the conclusions. (Like "with 90% confidence" or "90% likely). This seems to me to sound more like a careful scientific approach.
  12. Not quite: Yes, Maxwell's equations say the speed of light is invariant. But physicists had difficulty interpreting the meaning of this. In 1905, Einstein proposed his light postulate - which in effect says no matter what (uniform) speed you are traveling at, no matter what speed the source of the light is going at, you measure the speed of the light beam as the same value (i.e. invariant). No, Michelson Morley did NOT prove the invariance of the speed of light. MM just found no evidence for the ether. Their experiment said nothing about the invariance of the speed of light. (A number of later experiments, however, did verify the invariance of the speed of light). C is constant because the speed of light, c is invariant. Einstein's formula on how to combine relative speeds obeys this principle.
  13. From Hans Ohanian's book, Einstein's Mistakes - The Human Failings of Genius, p. 226: "(Einstein's) 1911 calculation of the bending of rays of light, which was based on the Principle of Equivalence, yielded a result half as large as the new calculation (in 1915) based on his new theory of gravitation. Einstein understood that the reason for this discrepancy was the warping of space, whereas the 1911 calculation had effectively included only the warping of time . . . (Thus) the bending of a ray of light in an accelerated box is half as large as the bending in a box at rest in a gravitational field. " . . . in 1913, Einstein's friend and colleague Ehrenfest . . . had published a short paper presenting a general proof about the failure of the Equivalence Principle for the propagation of light." As I understand it, Einstein deduced gravitational time dilation from the EP. From this, in 1911 he calculated the wrong-by-half value for the bending of light. By considering only the warping of time, Einstein's mathematics gave identical predictions as Newton's. (I do not believe he realized this at the time.)
  14. Sorry, but I do not think you are right here. Einstein came up with the EP in 1907. Based on the EP and his free-falling elevator thought-experiment, he calculated the bending of starlight as is passes very close to the Sun's surface. He got a value of 0.875 arcseconds. This is the same (incorrect) value predicted by Newtonian gravity. And it takes into account only the warping of time. Then in 1915, with his new field equations of general relativity, Einstein revised his prediction to twice the amount: 1.75 arseconds. Experiments since have confirmed this value to extreme accuracy. (This takes into account the warping of both time and space).
  15. Yes, MM failed to detect the ether. But it said nothing about the absolute speed of light.
  16. Do so-called climate-change deniers talk about uncertainty in their conclusions? Please let me know.
  17. The Equivalence Principle (EP) has its limits. The beam going across the spaceship will bend only half the amount of a beam in a equivalent graviational field. The EP takes into account only the warping of time, and in fact gives identical predictions as Newtonian gravity. General relativity gives the full effect due to both time and space warp -- which agrees with actual measurements of starlight passing the Sun.
  18. As I understand it, the Michelson-Morley experiments said nothing about light propagating at the same speed in all inertial frames. The MM experiments were done in a single reference frame -- the light source, the interferometric apparatus the light went through, and the detector (film?) were all at rest with respect to each other. So the experiments didn't prove or disprove Einstein's light postulate. Maxwell's theory says light is a continuously moving electromagnetic wave. The continuously changing electric part of the wave produces a continuously changing magnetic part. This in turn produces the electrical part. They produce each other. The key here is continuously changing. Einstein imagined moving at the same speed as a beam of light (at age 16!). Buit if he did, the beam would appear at rest with respect to him. So then the electric and magnetic fields would be static -- not changing. So they would not generate each other, and the EM wave would not exist from his poiint of view. As someone said, a light beam must move to exist. So, Einstein concluded, you can never catch up to a light beam. It always goes at the same speed no matter what your (uniform) motion.
  19. Thank you iNow. The evidence in the graphic is clear and compelling. As I said, the more I learn about this issue, the more I am convinced on human-induced global warming and the urgent need for action now.
  20. John B shows the data from 2000 to 2011 in post #209. Where may we find the longer data set chart you refer to. I apologize if you have already posted this chart.
  21. My understanding is the expansion does "tug" throughout galaxies. It is pushing space apart within our galaxy right now. But gravity (spacetime curvature) is pulling it together within our galaxy. Gravity within our galaxy is much more powerful, so it dominates -- thus stopping the expansion of space within our galaxy. See linkfor calculations on expansion within galaxies: http://answers.yahoo.com/question/index?qid=20110605063620AAapPXk So
  22. I do not assume malicious intent. Far from it. Thanks for the link, iNow. It shows the science behind the adjustments, which seem to me to be both reasonable and necessary. Because the potential impact of global climate change on human life (and other life forms) is potentially devastating. And the longer we wait to do something significant on a global scale, the harder it is to stop the consequences. And the more likely thousand or even millions of people will die due to our lack of action. And there may be some point of no return - when climate change is no longer correctable by human action.
  23. Got it. Thanks guenter.What are the physical implications?
  24. Suggest you read Brian Greene's book, The Fabric of the Cosmos. He presents an excellent physics discussion in lay terms on the nature of "time". It touches on some of the issues you raise. For example, per spacetime physics, an analogy for time is not a flowing river from past to future, but a block of ice with all of spacetime frozen and existing. He says we must think of all of time as "out there" just like space. Fascinating stuff! P.S. Please divide your writing into paragraphs. It would make it easier to read.
  25. Within galaxy clusters, gravity offsets the expansion. So the expansion is evident between galaxy clusters but not inside them. Thus the stars and planets etc. inside our Milky Way galaxy are not expanding. See link for how fast the universe is expanding: http://helios.gsfc.nasa.gov/qa_sp_ex.html#fastexp
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.