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Looking for other proof of expanding universe.

  1. Oct 15, 2012 #1
    The idea of an expanding universe is said to be proven by using the calculated distance of a Cepheid star from us, and the amount of change in the wavelengths of light emitted from the Cepheid star relative to us.

    There must be another way to prove the universe is expanding since the above is only proof if you assume that the change in wavelength is caused by the expansion of space. Is anyone aware of another method used to prove the expansion? Has anyone measured the distance of the same Cepheid star several years apart?
     
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  3. Oct 15, 2012 #2

    Vanadium 50

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    Did you look at the Frequently Asked Cosmology Questions? Is there something in particular that you find difficult?
     
  4. Oct 15, 2012 #3

    Drakkith

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    There is also the redshift of supernovas, quasars, etc. A very good indicator is type 1a supernovas, since they all seem to the same mass at the time of the explosion, their intrinsic brightness is the same. So the brighter an observed 1a SN is, the closer it is too us. This matches with the measured redshift of objects at that distance in accordance with hubbles law. IE we measure the brightness and redshift of a type 1a supernova and BOTH of the measurements fit our expectations and predictions. Correlating two different effects lets us be much more confident that our model is correct.

    Here is a link to the cosmological distance ladder. It lists the various methods that we use to determine the distance to objects in space. http://en.wikipedia.org/wiki/Distance_ladder
    You can see that there are many different ways of measuring distance. Having more than one way to measure the distance to an object, similar to what I said above, allows us to be confident that our techniques are indeed correct.

    The idea of a doppler shift in the wavelength of light is VERY strongly supported by all current scientific theories. We can actively measure redshift in a lab to a very high precision. When we apply that to our observations of the universe, we find that things are moving away from us. Our interpretation of this recession uses General Relativity, the most accurate theory dealing with gravity and very large scale objects like galaxies, clusters, etc. GR explains gravity as emerging from the geometric properties of spacetime. It is the framework of GR that allows us to explain the recession of galaxies away from us as an "expansion of space".

    Also, the amount of observations performed in astronomy are staggering. Not only by professionals, but by amateurs as well. Here is a light curve for the star Mira for the last 20,000 days, since 12 Jan 1958.

    http://www.aavso.org/tmp3/468617438.png [Broken]

    I pulled this from the AAVSO website in about 30 seconds. http://www.aavso.org/lcg
    So yes, we have observed variable stars over the course of several years. If you want to find data on a specific Cepheid variable just use the light curve generator at the link above.
     
    Last edited by a moderator: May 6, 2017
  5. Oct 15, 2012 #4

    Chronos

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    We also have observational evidence the universe was cooler in the past, which is precisely what you would expect in an expanding universe - re: http://arxiv.org/abs/1012.3164, and http://www.das.uchile.cl/das_ingles/new_temp_measurements.php [Broken].
     
    Last edited by a moderator: May 6, 2017
  6. Oct 15, 2012 #5

    Drakkith

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    Chronos you mean warmer?
     
  7. Oct 16, 2012 #6

    Chronos

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    I plead dyslexia.
     
  8. Oct 16, 2012 #7

    Drakkith

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    There's no pleading in Cosmology!
     
  9. Oct 16, 2012 #8

    Chronos

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    Cosmology is cruel.
     
  10. Oct 16, 2012 #9

    Drakkith

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    Cruel Cosmology, now offered at a college near you!
     
  11. Oct 16, 2012 #10

    Chronos

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    OMG, I think I am teaching that course! They will not take me alive.
     
  12. Oct 16, 2012 #11
    universe is not expanding only the galaxies are moving away from each other..like the shards after an explosion .space is infinite hard vacuum and these matter and energy is expanding into this nothingness and creating the familiar space that we know of ie space with underlying vacuum energy .UNIVERSE is not expanding !



    like in the above video the particles will move away from each other like normally would after an explosion ,space is not expanding ,if the movement of galaxies is because of expansion of space ,then all galaxies will be moving away from each other in same speed

    .idk why people invoke this kind of esoteric metric expansion like weird ideas .:grumpy:
     
    Last edited by a moderator: Sep 25, 2014
  13. Oct 16, 2012 #12

    Drakkith

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    This is wrong. You are under the impression that galaxies are moving away from us due to an explosion within space back at the "big bang". This is a classic misconception.

    Incorrect. Expansion is the only thing that explains the observed recession velocities. An explosion within space absolutely does not. And that video is not a realistic depiction of a grenade exploding, it is simply a movie someone made just to make it. In a real explosion smaller fragments are ejected at very high velocities while larger fragments are slower thanks to their larger mass. That video has them all intermixed.
    See here: http://www.phinds.com/balloonanalogy/

    Keep in mind that the redshift measured increases linearly with the distance of an object. An explosion within space would NOT do this.
    At the time of the big bang, everything was in the form of radiation and subatomic particles. A normal explosion would have pushed the lighter particles away faster than the heavier ones and would have had no affect on the radiation.
    We routinely measure recession velocities of objects that exceed the speed of light. If it were a normal explosion that caused the expansion this would be impossible per the rules of Special Relativity. Luckily for us General Relativity trumps SR and allows recession velocities to exceed c if they are non-local and due to the geometric properties of space. (IE if they are caused by expansion, not movement through space)
     
    Last edited by a moderator: Sep 25, 2014
  14. Oct 16, 2012 #13
    I heard recently that different frequencies of radiation have been measured to travel at different speeds on their way through space to us. Is it possible that this bias in the arrival time of different frequencies could affect our measurement of distances to objects?
     
  15. Oct 16, 2012 #14

    Chronos

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    A frequency dependent speed of light has been postulated under a variety of cosmological models. No such effect has been detected to date.
     
  16. Oct 16, 2012 #15
    Incorrect. Expansion is currently the only thing that explains the observed recession velocities.
    There are exceptions to the rule, and unexplained observations with galactic velocity fields that call into question expansion as an explanation of redshift.
    But seeing as there are no explanations forthcoming, expansion will have to do as a model for now, although it is fun trying to come up with alternatives, that's for other threads though.
     
  17. Oct 16, 2012 #16
    Not according to the glossy TV documentary I watched a couple of weeks ago. They reported well-observed and significant effects and discussed them with the researchers. All quite excited about it. I don't think I dreamt it but you never know.
     
  18. Oct 16, 2012 #17

    Drakkith

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    When discussing science one should always take for granted that if someone says something, the phrase "as far as we know" is implied.

    What exceptions are you referring to?

    TV documentaries are notoriously prone to giving out highly speculative and often incorrect information. Do not take them seriously unless you can find the same information from multiple sources, preferably peer reviewed sources.
     
  19. Oct 16, 2012 #18

    marcus

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    To elaborate on what Drakkith said, here is a constructive suggestion: You say they discussed the findings with the researchers! Another time if you could jot down the names of one or more of those who did the research, we could look their papers up.

    It's normally easy to do if you have the name and first initial of one of the authors.

    A celebrity scientist merely commenting on some younger person's work isn't usually very helpful. But if you give us the name of one of the researchers we might be able to find the actual scientific publication online.

    There have been some false alarms---seemingly exciting results that were not confirmed---so it's helpful to be able to find the particular announcement and publication that they were talking about.
     
  20. Oct 17, 2012 #19

    marcus

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    Grounded, are you still around?
    The current rate of expansion is 1/139 of one percent every million years. It sounds like you are asking that someone measure the distance to a star to within an accuracy of 1/139 of one percent, and then wait a million years and measure it again that accurately, to see if it is then farther away by that fraction of a percent. :biggrin:

    But actually astronomers do better than this all the time! For example with type 1A supernovae.

    These are all about the same intrinsic brightness and they follow the same approximate schedule day by day. Changing brightness and color. About 15 days to reach peak brightness, then falling off at a certain rather rapid rate for about 25 days, then dimming at a much more gradual rate for another 40-some days. The color changes are more subtle but detectable---different bands change according to a slightly different profile over time.

    With a z=1 supernova of this type, for example, we get the news of its day 5 LATER, because by the time it is doing its day 5 stuff (which is recognizable and we expect) it is FARTHER.
    So the news of what it was doing on day 5 only reaches us on day 10. Because it had to travel farther.

    We know to expect the peak brightness around day 15, but during the first 15 days of its explosion the star got farther away. So the news had farther to travel and we only get the news on day 30 of watching.

    This is essentially what you were asking people do with Cepheids, observe one now and then a while later to see if it has moved farther. Well YES, effectively this is done with that type of supernova.

    The watching schedule is retarded (compared with the explosion schedule) by the star getting day by day farther away and the news needing more time to get to us.
     
  21. Oct 17, 2012 #20
    the site you linked to says this

    untitled.jpg



    if expansion of galaxy clusters are "UNIFORM" in all direction then it is conclusive indication that galaxy clusters are indeed expanding due to metric expansion of space .

    http://astro.unl.edu/classaction/animations/cosmology/balloon.swf

    but unfortunately that is not the case ,different clusters are expanding itself and moving away from other clusters of the "cosmic web" at DIFFERENT rate

    now imagine you blowing a balloon and the pennies glued to the surface of balloon are NOT uniformly moving away from each other ?how weird would that be ?
     
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