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About NowThatWeKnow

  • Birthday 06/24/1949

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  • Location
    Tulsa OK.
  • Interests
    Aviation, computers, science
  • College Major/Degree
    Some college
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  • Biography
    Vietnam veteran, Design and sell RC aircraft on the Internet, Web site design
  • Occupation
    Professional pilot, Information Technology, early retirement


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  1. Using the GPS satellites to compare GR and SR corrections to clocks. "...Special Relativity predicts that the on-board atomic clocks on the satellites should fall behind clocks on the ground by about 7 microseconds per day because of the slower ticking rate due to the time dilation effect of their relative motion ...A calculation using General Relativity predicts that the clocks in each GPS satellite should get ahead of ground-based clocks by 45 microseconds per day..." Not sure of the exact #'s concerning the moon but but Earth's gravity (vs way out in space) will slow clocks by .022 seconds a year.
  2. And that is why it is called relativity, It is all relative.
  3. Wouldn't the "Lorentz transformation" be relative to the speed we observe and the "velocity addition formula" would show observed speed? Here is a length contraction calculator. http://www.cthreepo.com/math1.shtml
  4. I did catch the "center of the Milky Way" error but I took it as just an error in words and not a claim. The whole story was presented as one interpretation of a legend that some may believe is a prophecy. There were no claims that any of it was true other then a few things concerning the accuracy of their calendar and knowledge of astronomy. Anyway, that is the way I took it and I didn't leave wondering if the world was coming to an end in 2012. A little drama added to programs to help ratings. I find some of their stuff intertaining and other stuff pretty lame. But I do not see it as "gross misrepresentation AND outlandish claims". If that is what you got from that clip then our minds work very differently. Enough said a bout the History channel. Merged post follows: Consecutive posts merged The History channel UFO programs are usually pretty bad. I have only seen one or two that were worth watching. Most get turned off in the first few minutes.
  5. While I do see the History channel present a different point of view often, I see it being done with interest in a factual and not misleading way. I have never heard any outlandish claims as facts and their speculation is obvious to me when I watch it. I challenged people awhile back to point out a specific gross misrepresentation of the truth, considering a layman approach, and I am still waiting.
  6. Thank you, I think. I have no training in cosmology and most of what I know is from reading and posting in the last few months. It does seem that most examples of frames have to do with motion of one object relative to another. And if you are in the same frame you will share the same time. I would like a definition of a "frame" that I could understand but would also make sense to you. Maybe I should have said that I heard the universe was flat, not space. I know you do not think much of the History channel but they said that during measurements, the triangle totaled 180*. And on a scale our technology was capable of dealing with, the universe was flat or nearly flat from what we can tell. I guess that kind of goes along with what you are saying.
  7. A frame could be any number of coordinates where there was no motion relative to each other and, considering GR, they would also have to share the same gravitational potential. Is that not right? It wasn't long ago I heard that our current technology indicated space was flat, or so nearly so we could not determine any curve. Is there new proof that space is curved?
  8. Didn't you say that you could be anywhere in the universe and that the age of the universe would be the same when calculated as long as you had a constant CMB temperature in all directions at each location? Wouldn't that make it a common reference frame?
  9. Thanks for your reply. My question has been answered. As far as ignoring GR, I just didn't want local gravity having an impact on the clocks and complicating things. Merged post follows: Consecutive posts merged My thoughts exactly. If nothing else, it would make sense for us to choose it as a "preferred reference frame". Then make adjustments for local gravity and we would have a universal GMT (Zulu) time. Edit - Or master clock as swansont would prefer
  10. It was put this way in a different thread. "Earth says it is because he aged slower, and he says it is because the distance was shorter. Either explanation is equally valid (There is no one right explanation.)" I found it easier to understand the twin paradox when I started with how acceleration affected the clock speed. Then I could add other components of the story and it made more sense.
  11. Knowing "how much" takes specific information. We do consider "how much" when we talk about the GPS satellites or 1G rocket rides to a particular location. I see everything as a clock. The rate of decay of road kill measures time.
  12. To make things a little less abstract I would like to ignore GR in my scenario. The variable gravitational fields only complicate things when considering if two separating galaxies can share the same time frame. My only concern is if expansion of space causes time dilation and length contraction and at this point it seems it does not. My twin example had both twins leaving Earth. I was just contemplating if it was possible for separating mass because of movement, not expansion, to share the same time frame. It seems it is possible but length contraction may be a different story. As I am sure you can tell, I am very much a layman just trying to understand it all a little better. I do appreciate all participation as it is all food for thought.
  13. Not sure what you mean by "time dilation of the Earth". The space twin accelerates out of Earth's frame and because of that his clock will run slower.
  14. Not sure what you are saying here but my point was that the two twins could blast off in any direction and their clocks would remain synchronized as long as their acceleration was equal. Both of their clocks would slow down, relative to Earth clocks, equally. Any course or speed change after blast off by either twin would unsyncronize their clocks.
  15. Isn't the CMB thought to be the photons from the early universe?
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