# IM Egdall

Senior Members

591

1. ## Approaching the speed of light

Sorry, I am not understanding you. What do you mean by time stops "after a certain region in space"? We know time slows down in a gravitational field. (This has been observed many times in all kinds of tests.) The idea for an event horizon is that gravity (spacetime curvature) is so great that time slows down to the point where it stops altogether, as seen from far away. You are correct that, I as far as I know, this stopping of time has not been observed (yet). But it is a prediction contained within the construct of general relativity, which has been tested extensively in nearly all its other predictions. And what do you mean "an object should at least get smeared throughout the surface of the black hole"? Plus I never said the atoms are measured both inside and outside the event horizon of a black hole. Please clarify.
2. ## What does the Doppler effect say about light's motion?

The Doppler shift affects our observation of the frequency of light. It does not affect our observation of the speed of that light. To model how our relative motion affects the speed of light and the speed of other thing, Einstein came up with a clever formula. See link: http://math.ucr.edu/...R/velocity.html Per this formula, the speed of light is always the same value, c (about 670 million miles an hour), no matter what the speed of the light source or the speed of the observer. The speed of a particle with mass (and objects which they are made up of) is always less than the speed of light, c. And per Einstein's formula, no matter what your speed or the speed of such an object, the combined speed is always less than the speed of light. In other words, no matter what your point of view, your (uniform) reference frame, you will measure the speed of light as the same value c. And no matter what your reference frame, you will measure the speed of particles with mass as less than c. My website: http://www.marksmodernphysics.com/
3. ## More than one Big Bang Theory

Science is a work in progress. The big bang theory is our best current theory of the creation and evolution of the universe because of all the evidence confirming its predictions. Hopefully some day string theory or some other theory of quantum gravity will tell us what happened at time zero of the big bang -- an unknown in the current big bang theory. And maybe a new theory will tell us what happened, if anything, before the big bang. To make the generalization that "the experts do not believe in the big bang" is ridiculous. As Swansont put it, when someone says "the experts" but gives no names, this should raise suspicion. Name your experts, please.

According to special and general relativity, there is no absolute time. And measurements of time on Earth, in airplanes, rockets, and satellites etc. verify Einstein's predictions to great accuracy that time is relative. However, as I said in another thread, I think the expansion of the universe gives us a basis for a cosmic or universal time.
5. ## Is energy transmission medium contingent?

I was responding to a request for a link on the idea of an ether to conduct EM radiation and the fact that the Michelson-Morley experiments failed to find evidence for it. Why do you think its a joke?
6. ## Approaching the speed of light

What goes on at the event horizon of a black hole is based on solid science. It is a prediction of the theory of general relativity, our best current theory of gravity. A vast number of observations, tests, and measurements have confirmed nearly all other predictions of Einstein's theory, including a number of phenomena just outside black holes. If and when an even better theory of gravity comes along (if ever), we may get a deeper understanding of the interior of black holes.

I suggest you read Brian Greene's book, The Fabric of the Cosmos. It has a wonderful discussion on our understanding of time, and is written for a lay audience. I think it will answer your questions and pose new and interesting ones for you to think about.
8. ## Approaching the speed of light

Per Einstein's general relativity, gravity is the warping of time and space. This "spacetime curvature" affects the path of all particles, including massless photons (light particles). For example, light from a star passing very close to the Sun is bent or curved by the Sun's spacetime curvature. The verification of this effect in a 1919 solar eclipse made Einstein world famous. Consider light inside the event horizon of a black hole. Here spacetime curvature (gravity) is so great that space is stretched to the point where the frequency of that light is stretched to zero. So no light inside the event horizon is emitted to the outside world. Light is an electromagnetic wave, with regular peaks and valleys. You can think of each peak and valley as the tick and tock of a clock. So when light's frequency is stretched to zero, it is equivalent to "freezing" time. Thus to an observer far away, time at the event horizon of a black hole appears to stand still. See link for more details: http://imagine.gsfc....rs/970618a.html My website: http://www.marksmodernphysics.com/
9. ## Size of the Universe?

Per special relativity, nothing can travel through space faster than the speed of light. But per general relativity, space itself can and does expand faster than the speed of light. According to inflation theory, moments after the big bang, the unverse underwent an exponential expansion faster than the speed of light before it settled down to its current expansion rate. See http://en.wikipedia.org/wiki/Inflation_(cosmology) Plus at a far enough distance from us, from our point of view space right now is expanding faster than the speed of light.
10. ## How can time "begin"?

I think the expansion of the universe gives us a kind of cosmic timeline we can all refer to. From this, we can estimate the age of the universe and when the big bang occurred.
11. ## Infinity

Good science is not based on preference but reasoning and independent confirmation of a theory through empirical evidence. The big bang theory is one such theory. It is the best scientific theory we have on the creation and evolution of the universe due to all the evidence which supports its predictions. See for example: http://en.wikipedia.org/wiki/Big_Bang#Observational_evidence. You can also google "age of universe" to see the scientific reasoning, calculations, and evidence for the 13.7 billion-year age of the universe. For example, see: http://www.astro.ucla.edu/~wright/age.html
12. ## Dark energy as vacuum fluctuations of photons?

Interesting paper by physicist Bruno Deiss where he proposes a solution to cosmological constant problem. http://arxiv.org/pdf/1209.5386v1.pdf Problem: Vacuum fluctuations of quantum mechanics could account for the so-called dark energy which is causing the expansion of the universe to accelerate. But calculations say vacuum fluctuations are some 100 orders of magnitude too large. Deiss Solution: Only virtual photons and maybe the lightest virtual neutrinos contribute gravitational effects - hence dark energy. In his model, all the other virtual particles in vacuum fluctuations do not contribute gravitationally. Only particles within a limited energy range interact. His calculations show this solves, at least in part, the mystery of the cosmological constant problem and dark energy. There are a number of assumptions here, including that spacetime is discrete and that the expansion of space is quantized. Plus there are issues in his model with expansion before the era of recombination, unless yet to be found particles exist. Even so, I thought it was a clever approach to solving this long unsolved problem. Any thoughts on this? My website: http://www.marksmodernphysics.com/
13. ## Is fusion power the way forward?

Back in the 1970's or 80's, I worked on optics analysis for a govt. laser fusion energy project. And we are still so far away from a viable solution. How many millions (billions?) has the govt. spent on this over the years. How many solar panels or wind farms or or geothermal factories or even fission nuclear plants could we have built with this money? Wouldn't we have been better off using the funding in a more realistic, near-term alternate energy source to oil?
14. ## High speed black holes

In spacetime physics, momenergy is the source of gravity (spacetime curvature). It is made up of rest mass, energy, and momentum. See link: http://www8.hp.com/u...Display=drivers Mywebsite: http://marksmodernphysics.com/
15. ## What - or "when" - is the present?

See link http://www.youtube.com/watch?v=b_PtnzqxEFQ THis is one of many web demonstrations of Einstein's "light clock" thought experiment. The speed of light is unaffected by the speed of the observer or the speed of the source of the light. In other words, you always measure the same speed for a beam of light (in a vacuum), no matter what your speed. The video shows how this principle leads to the slowing of the passage of time with relative motion. Hope it helps answer your question.
16. ## theory on black

s For a non-spinning black hole, there is a single point at its center where all the matter/energy of the collapsed star is. And there is an event horizon, a spherical surface some distance from the center. So the center of the black hole does not coincide with its event horizon. A person falling into a black hole is in free-fall. From his perspective, he is at rest and the event horizon is coming up towards him. There is no special feeling when he crosses this event horizon. To him, he is not frozen in time. As he approaches the center of the black hole, his body is stretched vertically and squeezed horizontally by the intense gravity, and he does not survive to experience the very center. At least this is the theory, as no one has fallen into a black hole. And even if someone did, he could not communicate the experience to those of us outside the event horizon. See link: http://casa.colorado...ajsh/schw.shtml
17. ## Redshift.

Georges Lemaitre discovered the galaxy distance-redshift relationship several years before Hubble. Using Einstein's field eqautions of general relativity, Lemaitre predicted the expansion of space. He said the frequency of light from distant galaxies is stretched by the expansion of space as it makes its way to us on Earth. The further away the galaxy, the more time its light takes to reach Earth. Thus the more space has expanded during this time. So the greater the distance to the galaxy, the greater the expansion and the greater its light's redshift. See link: http://decodedscience.com/georges-lemaitre-discovered-the-expansion-of-the-universe/5588
18. ## Is energy transmission medium contingent?

http://en.wikipedia.org/wiki/Luminiferous_aether
19. ## speed of light c

I believe that in a medium such as glass, light is absorbed by an electron in a molecule within the medium and is then reemitted. It is then absorbed by an electron in another molecule and reemitted. Etc. It takes some time for the electron to reemit a photon(actually a new photon) each time. This is why light travels slower in glass. But the photon still travels from electron to electron at the speed of light.
20. ## Who here is a global warming skeptic?

You make a good point here. I believe nuclear energy is the best solution to reducing our carbon footprint. But the public fears nuclear power, made worse by the recent incident in Japan. Plus nuke plants are very expensive to build. Why don't our leaders push for nuclear power to stave off global warming? Because they don't have the consensus of the voters on both issues. Their first priority is to get elected. I for one find this very frustrating. Maybe nuclear power isn't the perfect solution, but it is the best available one. It seems to me many more people will die due to the effects of human-induced climate change than from the risk of nuclear power.
21. ## Describing General Relativity Thought Experiments

One thing comes to mind: Special relativity applies to objects in uniform motion, that is objects which travel at a constant speed and in a constant direction. A star as seen in the Earth frame of reference is rotating around the Earth. Its direction is constantly changing. So special relativity does not apply here. Non-uniform motion is the venue of general relativity, where there is no speed of light restriction.

23. ## Describing General Relativity Thought Experiments

I believe romesh is referring to frame dragging in general relativity. We can think about the bulge of the Earth from two points of view: 1) Reference frame above Earth. Here the Earth is seen to rotate, and this rotation results in the bulge at its center. 2) Reference frame on Earth. Here the Earth is stationary and the rest of the universe is rotating. So from this point of view, the Earth's bulge is caused by the rotation of the rest of the universe. I think this is romesh's question: As we consider stars farther and farther away from the Earth, from the Earth reference frame they are rotating faster and faster. A star far enough away appears to be rotating faster than the speed of light. But there is no information here which is traveling at the speed of light, so it does not violate special relativity. Did I get this right?
24. ## Global Warming

m I dreaming? I picked up my Wall Street Journal today and there it was on the Opinion Page: "A New Climate Change Consensus". In my experience, the Journal has had editorial after editorial, article after article claiming global warming is a hoax. Now all of a sudden, Fred Krupp's article -- quoting its owner Rupert Murdock and others -- says it's real and we must all get together to try to solve the problem. Halleluya! Maybe the tide is turning, and we will finally do something about it. Link to article: http://online.wsj.co...eTabs%3Darticle
25. ## IM Egdall

Sounds very interesting. Always looking for better ways to explain to my students. I'd be happy to review it. I tried looking at it and it said LOCKED. What do I do?

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