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Thread: Light and sight

  1. #1 Light and sight 
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    Can someone please explain how vision works? I always heard when you look up to the stars it's like looking into the past. Even our sun, when we see the sun we're seeing the sun as it was 8 minutes ago. Can someone explain this further? And when we see everyday objects how does it work? Is light reflected off the objects and then back into our eyeballs? When we see everyday objects are we seeing them as they were billionths of a second into the past? And if looking great distances away is like a time machine...say there was a gigantic mirror in space that is 1 light year away and we had a really good telescope, could we look at that mirror and see earth 2 years into the past? This is so very interesting to me, any response would be greatly appreciated.


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  3. #2  
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    Quote Originally Posted by savage View Post
    Can someone please explain how vision works? I always heard when you look up to the stars it's like looking into the past. Even our sun, when we see the sun we're seeing the sun as it was 8 minutes ago. Can someone explain this further?
    Electromagnetic radiation, including light, is limited to "c" when traveling through spacetime. Spacetime is, of course, any space within the Universe and "c" is the constant equal to approximately 300,000 kilometers per second.
    Since the sun is far away from us, even at those incredible speeds, photons must travel for about 8 minutes before it reaches us.
    The light that reaches you from the Sun started its journey from the surface of the Sun 8 minutes prior to reaching your eyes.
    Quote Originally Posted by savage View Post
    And when we see everyday objects how does it work? Is light reflected off the objects and then back into our eyeballs?
    Light is scattered. As in- really scattered. Some of the light reflected off of objects is within light of sight- that is; a straight line from the object to your eyes.
    What reflects in any direction that is not toward your eyes is not 'sighted.' So if for some odd reason, light did not reflect in your direction off of an object then you would only see a shadow where the object was.
    Once light meets your eye, it travels through the cornea and a Lens where the image is focused onto your retina.
    Your retina is composed of highly specialized cells. These cells contain a compound that has a chemical reaction to wavelengths of light. Different wavelengths will have different reactions, which is why we can see within a narrow band of colors. Bees retinas are more reactive to more wavelengths and they saw a broader range of colors than we do.
    The chemical reactions from the light are converted into voltage by yet more specialized cells attached to the cells in your retina. The voltage is carried by the optic nerve to the brain where the voltage is then converted into a series of chemical compounds which stimulate different portions of the brain allowing your brain to interpret it as an image.
    Quote Originally Posted by savage View Post
    When we see everyday objects are we seeing them as they were billionths of a second into the past?
    Yes, ehh... approximately...
    Quote Originally Posted by savage View Post
    And if looking great distances away is like a time machine...say there was a gigantic mirror in space that is 1 light year away and we had a really good telescope, could we look at that mirror and see earth 2 years into the past?
    Yes. Of course, the further you go back, the bigger the mirror and the bigger the telescope you would need to gather enough scattered light to have resolution to see the Earth.
    To look back to the time of the Dinosaurs, for example, would require mirrors larger than the solar system. And even then, you wouldn't see much... The photons reflected from the Earth would have interacted with other material in the last 65 million plus years.


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