Why can the James Webb Space Telescope “see back in time” and see the first few moments after the Big Bang when it already happened?

13 Answers

  • YKhan
    Lv 7
    6 months ago
    Favorite Answer

    It really won't let us see just a few moments after the Big Bang, unless you consider 100 million years after the BB to be just a few moments after. That's about 13.7 billion years ago, with the whole universe being only 13.8 billion years old. So it'll let us see a little bit further back, but not all of the way to the beginning.

    Currently, the furthest back in time we can see is with the Hubble telescope, which sees as far back as 13.2 billion years ago, or about half a billion years less further than JWST. Actually, the Planck telescope, which measures the cosmic microwave background radiation can see even further back than either of them, as it is looking at light that left just 300,000 years after the Big Bang, not several hundred million years after. But the Planck telescope is only measuring overall whole-sky fluctuations in light brightness from that period of time, and it's not concentrating on any particular spot in the sky, like the Hubble or JWST.

    The reason that any of these telescopes can see that far back is due to the fact that it takes light billions of years to travel to Earth from these far away places. So we're seeing objects as they looked billions of years ago, not as they may look like now.

    Now the reason that the JWST can see further than Hubble, and Planck can see further than either of them, is due to wavelengths of light that they are tuned to look at. Hubble was tuned to look at light going from the large-wavelength near-infrared to the short-wavelength near-ultraviolet portions of the spectrum; so that spectrum had the human-visible portion of the spectrum also included in between. JWST is tuned to look at only the full-infrared spectrum, from far-infrared to near-infrared, which means it sees more of the infrared spectrum than Hubble does. Planck on the other hand is tuned to view the microwave spectrum, which is even larger wavelength than the infrared.

    The larger the wavelength the farther in distance they can see, and the further back in time they can see. Due to the expansion of the universe, wavelengths of light that were once visible by the human eyes, have gotten stretched to wavelengths that are longer and outside of human vision ranges. The further back in time and distance the light is, the longer it has been stretched. Since the Hubble could only see back to the near-infrared, its vision stops around 13.2 billion years ago, as beyond that, the wavelengths of light are way longer even than Hubble can see. JWST is tuned to see back to 13.7 billion years ago, as it can see longer wavelengths of infrared. 13.7 billion years ago is when it is expected that the first stars were lighting up. But the furthest light back after the Big Bang is now in the microwave region, and that's where Planck sees.

    • Morningfox
      Lv 7
      6 months agoReport

      I beg to differ about Planck "not concentrating on any particular spot in the sky." It had a resolution of 5 to 33 arc-minutes, depending on the wavelength. That's a pretty small patch of the sky.

  • Tom
    Lv 7
    6 months ago

    it sees the LIGHT that has not reached Earth Yet.

  • Anonymous
    6 months ago

    The visible universe dates to the Epoch of Recombination 379,000 years after the Big Bang. But we can see the CMBR which is the primordial universe, back to Planck's limit.

  • Clive
    Lv 7
    6 months ago

    Same reason as ANY telescope can effectively see back in time. It takes light time to travel so we see any star or galaxy only as it was when the light left it. So what you need to see further back is a telescope that is so big it can detect light that has travelled even further. And the JWT will do this because it's designed to work mostly in the infrared.

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  • 6 months ago

    Because the JWT will focus on as far away as possible

    The Speed of Light IS 186.000 MPS

    A Light Year is the Distance that Light can travel in a year

    For an object that is 1, 000 Lys away

    It takes 1,000 years for the light from it to reach us

    The farther an object is distant, the longer light has to travel

    For an object to be almost 17 Billion Lys away it must have existed pretty close to the beginning of the Universe

    The whole of History lies out there

    If you cold see Earth from a distance of 80 Million light years it is possible you could spot a Dinosaur

    There is a reason for looking as far back as we can

    We could finally settle the argument of how the Universe actually formed or even what led up to it

    It could truly be the Final Frontier

    Attachment image
    Source(s): If time actually began at the moment of the Big Bang, we could solve that argument too
  • 6 months ago

    Same reason the HST can do the same, just that the Webb telescope is far better, larger aperture, better resolution.

  • poldi2
    Lv 7
    6 months ago

    Because light takes a finite time to get here, so looking out into space means seeing the light that left an object in the past.

  • 6 months ago

    The same way you can "see back in time" and read a newspaper printed on the day you were born.The JWST will see light that has been on its way to us for 13 billion years. You can read a newspaper that has been on its way to you for 12 years (or however old you are).

    I don't think its important for your question, but the JWST will not see light from the first few moments after the BB. That light was doesn't exist any more ... it was absorbed by the super-hot gas that filled the universe back then. The JWST will (we hope) see light from some of the first stars, which started shining about 300 MILLION years after the BB.

  • Bill
    Lv 6
    6 months ago

    light moves away from its source at a constant rate and as the event happened millions of light years past , the telescope now sees that light as it passes on it's way, hence we are seeing the past as it is happening

  • 6 months ago

    It takes light time to travel to earth. We can only see the light that enters our telescopes or eyes. If a galaxy is 13 billion light years away, it took 13 billion years for its light to get here. So we are seeing what was there 13 billion years ago. Its impossible to see what is there right now.

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