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How can radiation from the Big Bang come from all directions?

  1. Oct 29, 2015 #1
    If radiation from the big bang has been traveling away from it's origin, how can it arrive at the same point from opposing directions?
     
  2. jcsd
  3. Oct 30, 2015 #2

    marcus

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    The CMB radiation did not originate at the start of expansion. That is the most ancient light and we detect it coming in roughly the same from all directions. It started on its way around year 370,000 when the hot gas filling space cooled enough and thinned out enough to become transparent.

    I don't understand the problem. Why shouldn't it come from all directions?
     
  4. Oct 30, 2015 #3

    Orodruin

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    I believe you have a very common misconception about what the Big Bang was. The Big Bang was not an explosion at a point in space which threw out material in all directions. It is the start of the expansion of space itself from a very small size and it therefore did not happen at a point in space, but occured everywhere at once. Since it happened everywhere, in particular it happened at the places in the universe where it would take exactly the age of the universe for light to reach us (modulo marcus' comment that the CMB did not really release at time zero). The CMB from positions which were closer has already passed us and the CMB from places further away might reach us later or never depending on the current expansion of the universe.
     
  5. Oct 30, 2015 #4

    bapowell

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  6. Oct 30, 2015 #5
    From _inside_ an explosion its energy comes from everywhere around any point. We are nor have never been outside, so it is completely logical that CMB comes from all around us.
     
  7. Oct 30, 2015 #6

    phinds

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    The big bang was not an explosion.
     
  8. Oct 30, 2015 #7

    Orodruin

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    As pointed out in #3 already.
    Please read the entire thread before replying. In particular when you are not familiar with the subject on a sufficient level.
     
  9. Oct 30, 2015 #8

    phinds

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    OOPS. I"m usually more careful in reading threads.
     
  10. Oct 31, 2015 #9
    I believe you're using "space" in one of two possible senses here, as the immaterial separation between objects, or between an object and its components. Where this gets confusing is that it had always been generally taken to mean the immaterial expanse beyond all objects, as well. The more specialized meaning you're employing is scientific, since science relies on evidence (real or hypothesized), but I think that people making a "beginner" post will tend to be using the more general meaning, which is much older. If there are mathematical or other reasons why you think I might be mistaken about this, I'd appreciate it if you'd bring them to my attention.
     
  11. Oct 31, 2015 #10

    phinds

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    There is no such thing as "beyond all objects" according to the Cosmological Principle.
     
  12. Oct 31, 2015 #11
    Well, yes, but the descriptions of the Cosmological Principle rely heavily on the term "universe", which, being a compound word (from Latin "unus versus", or "all together"), is very likely to be a newer word than "space" (from Latin "spatium", or "space"). Scientific concerns have found expression at least since Anaximander, but people had been talking plenty earlier than that.

    Understand, I'm not trying to knock Ordurin's main point, which is that the Big Bang was more temporal than (in the scientific sense) spatial: I'm just saying that implying that space was created, or that all of space expanded, can confuse people who are not fully aware that the word's being used in a more recently specialized sense. "Outer space" was the usual way to differentiate the variety that was felt to be unbounded even as recently as my own childhood, and, of course, its own bound (the inflating region) was hypothesized (with some supportive evidence) much more recently than that.

    The failure of that 20th-Century differentiation is probably what has people failing to differentiate the "between objects" part of space from the "beyond objects" part of it at all: Unfortunately, I'm sure it also has a lot of people who glance at scientific matters concluding that science includes more mystical gabble-de-gook than it really does.
     
    Last edited: Oct 31, 2015
  13. Nov 2, 2015 #12
    Yes you are right, it is not if you mean a _chemical_ explosion, but some name has to be given to such an energy burst, and even the "bang" word relates to sound, so the word "explosion" is as valid as any other to describe that. Thanks.
     
  14. Nov 2, 2015 #13

    phinds

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    No, it is not. "Big Bang" was given as a dirisory term and is now just a name that has a specific meaning. "Explosion" also has a specific meaning and is NOT one that is appropriate as a name for what we call the "big bang".
     
  15. Nov 2, 2015 #14
    "
    Phinds is right on this one. As Guth points out in The Inflationary Universe , if The Bang's closest resemblance had been to an "explosion", that part of the Big Bang's oldest layers which has turned into visible light would be visible as a very marked concentration of light in one part of the sky unless our current location had been its center at the time of its occurrence, and, since the earth is only some thousands of miles across whereas the observable universe has a width of many trillions of miles, that last possibility is phenomenally unlikely to have been the case. (It would also have had Copernicus spinning in his grave.) Its closest resemblance was actually to an extremely rapid "expansion" or "inflation", as in the usual analogy to the expansion of a cooking pudding containing, as its raisins, either incipient local universes (-like our own, which is much larger than the part of it we can observe) or incipient clusters of galaxies. The main difference would've been that the cosmic expansion involved cooling rather than cooking.

    The reheating that occurred, when quantum fluctuations or perturbations ended the expansion locally, produced that "hot dense soup of particulate energy" which provided the usual description of the Bang during the three decades between the failure of Hoyle's Steady State cosmology and the development of the inflationary cosmology that admits the possibility of numerous local universes, and it is that nearly exponential expansion which seems to have occurred during part of the time between the present day and an original Big Bang on a much smaller spatial scale that has rather confusingly pre-empted the term "inflation", just as the "space" popularized by sci-fi writers has interfered with use of the term "separation", which might've provided a much more specific one for the physical gaps between any entities with mass. However, such alternatives as the one developed by Hawking in his No Boundary Proposal, and elaborated in 2003 by Aguirre and Gratton, leave it unclear whether that earlier Big Bang even occurred.
     
    Last edited: Nov 2, 2015
  16. Nov 2, 2015 #15
    This is a common misconception. I held it myself at one time. The myth is that Hoyle chose it to poke fun at the theory when promoting his own Steady State concepts.

    Hoyle first used the term publicly in a BBC broadcast in the late 1940s. Some proponents of BBT, interpreted the term, as you suggest, as derisory. However, Hoyle maintained he had no such intention and was simply looking for an expression that would convey something of the nature of the event to a lay public.
     
  17. Nov 2, 2015 #16
    Ok the radiation comes fron all arround because the universe is an hipersphere.
    But
    Why are we looking at that adiation as an old photo? That keeps Showing us the same face forever
    That radiation emited photons, that are arriving to us today after a 14500000000 years aprox, but why do the photons keep arriving forever, it should be like an old movie that you can see it or loose it, after it is gone it is gone because the photons emited at that instant, reached us and kept going past us forever gone.
    But we keep looking at the short wave radiation like if it kept glowing forever and we know that after it became a transparent universe it should have stped glowing
     
  18. Nov 2, 2015 #17

    Orodruin

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    You are right, the CMB is changing. Today, we are receiving CMB photons which were emitted closer to us than the ones we will receive tomorrow. However, the regions of relatively constant temperature were large enough to make this a very very slow change.
     
  19. Nov 3, 2015 #18
    Ok, the emission area was big and kept expanding, and that is the area covered by the short wave radiation that today cover the inside of the sphere we can see all around us, but I question about the thickness of that photon train reaching us.

    It started at the big bang supposedly, then stopped after 300,000 years when the universe became transparent to energy and atoms formed, then the photon train should have been just 300,000 years long and a very small probability for us to catch that brief 300,000 year photon train after 14,500,000,000 years.

    The only solution I see, is that the photon train´s end, is receding from us at light speed, fact that is confirmed by the fact that we don’t see the photon train go past us, it just keep getting cooler and longer wavelength.

    That would mean we have a speed gradient with that photon train end, equal to light speed and that time, has stopped for us concerning that photon train, but then why at that particular time???

    Another explanation I see, is that every space region that has a speed gradient with us equal to light speed, keep freezing its photons that go past us and showing us a photo face and not a movie, a photo face that just keep getting cooler and not going past us, in other words, a frozen photon train wave.

    If we see those photos at 14,500,000,000 light years, it may mean that, that is the only distance we will forever see, because a photo never change, just gets cooler and cooler and its wavelength longer and longer until it is no longer detectable.

    Then it would mean, that the universe is not that old, just that we cannot see past that distance, because at that distance, the space is growing at light speed between us.

    Another inconsistency I see, is that, that 300,000 light year photon train, reaching us, keep going past us, because we are catching those photons and each end every one of those photons have energy, energy lost from the photon source; and that explain why we can see the source cooler and cooler. We are seeing a spring getting longer and longer and going past us without emitting more energy, just spreading over a longer distance or bigger space.
     
  20. Nov 3, 2015 #19

    Orodruin

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    No, you are missing the fact that this happened everywhere. And we cannot see the photons which were around more than 300000 years ago, they were quickly reabsorbed in the hot plasma. The background radiation which reaches us now was released when the Universe was about 300000 years old and the Universe became transparent. Because this happened everywhere, there are places which are so far away that the light from that time has not yet reached us. The CMB we see today are the photons which come from exactly so far away that it took them 13.4 billion years to reach us. Photons from places which were further away when the Universe was 300000 years old will form the CMB of tomorrow and that of 50 years from now.
     
  21. Nov 3, 2015 #20

    phinds

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    @Rafael Munoz m you completely misunderstand the CMB. There IS no "photon train". We are seeing photons that were all emitted in a much shorter span of time than 380,000 years, but that happened 380,000 years after the singularity, in a process called the "Surface of Last Scattering". The photons that we see today were emitted from a region of the galaxy that was on the Surface of Last Scattering and is a distance away from us that make it such that the photons are reaching us not. In a billion years, we will be seeing photons what were emitted, ALSO from the same Surface of Last Scattering, but from positions that were enough farther away that their photons don't reach us for another billion years. This just goes on forever, although at some point the photons from the Surface of Last Scattering that we "see" are from a distance so large that the photons have been red shifted beyond detectable.

    EDIT: I see orodruin beat me to it.
     
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