If the universe bends in itself would we not see light coming from everywhere?

Some people and scientists say that the universe is bend into itself and that if you go long enough into a straight line into one direction you will end up at the starting location. Now this makes me wonder what happens to ALL the light that is emitted by all the stars in the universe? If that light cannot go outside the universe but only travels in circles through the universe, why don't we see an all illuminated universe?

Would this indicate that the universe is by no means bend into itself?

11 Answers

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  • 2 months ago

    This is known as Olber's Paradox.  It doesn't happen because distant points are receding faster than light and it can never complete the journey.

  • 2 months ago

    We do see light from stars and cosmic background radiation coming from all directions. If the universe is closed, light hasn't had time to circumnavigate the universe. Its circumference is much greater than 14 billion light years. 

  • neb
    Lv 7
    2 months ago

    I think @dixon has a very good answer (have to say that here because the idiots at YA have done away with comments)

    As an FYI, general relativity is a theory of intrinsic curvature. That means curvature that can be detected from within the 4 spacetime dimensions. The complex mathematical description of that curvature is the Riemann curvature tensor which is a measure of how a vector changes when parallel transported along a path. Space is ‘flat’ if the spatial components of the curvature tensor are zero.

    General relativity doesn’t ‘know’ about extrinsic curvature or more complex topologies so there  is also another answer to your question. There are topologies where the intrinsic curvature of space can be flat - consistent with observation - but can also result in light being ‘bent’, possibly back to its origin. One of those topologies is a 3-torus, a donut with a 3-d surface. There has been an observational attempt to determine if the universe is one of these topologies, but it has failed to detect any evidence - likely for the reasons others have cited in their answers.

  • 2 months ago

    Some people and scientists say the universe is flat, just like experimental evidence from the Planck, WMAP missions and Boomerang experiment tell us. In that case there is no need to ponder going round in circles or light going around corners.

    Experimental evidence seems to be falling out of favor these days. It is always best to base any scientific model on any evidence available. The tendency these days is to make up a model to support what belief is most popular or most "beautiful", then do one's darndest  to deny all evidence that conflicts with the model. This is called "ironic science": the science you do when you are not doing science. Always be skeptical of a model ("theory") that appeals to popular perceptions of astronomy, or that appeals to oddball ideas, or that relies on impossible observations. Go for simplicity every time. Occams razor has served us well. It is about choosing the simplest model consistent with all known data. A curved universe does not fit such a picture.

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  • cosmo
    Lv 7
    2 months ago

    Good thought, but...

    The distance along a closed circular path around the Universe is about 10^22 lightyears, which is a trillion times the distance to each observer's event horizon.

    Basically, the expansion of the Universe sucks all the energy out of a photon before it gets anywhere near going all the way around.  The recessional speed of distant regions is faster than the speed of light (this is not forbidden in General Relativity), so the photon cannot get out of its local region of the Big Bang.

    In any case, we DO see some photons coming from all directions at all energies.  The Cosmic Microwave Background is fully saturated in the radio.

  • 2 months ago

    No

    It is Gravity that causes the Lensing effect

    Nobody knows where the Universe ends

    If at all

  • 2 months ago

    Even if the universe were bent onto itself, space itself is expanding. Everywhere. All the time. The effect of expansion is to add new space in between each bit of space. Locally, the effect is very small. Over long distances, it adds up.

    Pick a point in front of you, at a distance of 13,800 million** light-years. In between you and that point, the amount of new space being added every second is approximately 300,000 km.

    300,000 km/s is approximately the speed of light.

    Therefore, even if you were travelling at the speed of light, you would never reach that point... never mind making it all around the universe.

    On Earth, the surface is bent upon itself, and it is static (it is not expanding). Therefore, it you start off in one direction (does not matter which one) and continue in a straight line for 40,000 km (approx.), you'd be back at your starting point.

    Back to our universe. Because of the expansion of space, any object that is further away than 13,800 million light-years cannot be seen. For any photon leaving such an object and coming straight at you, the amount of expansion (new space) between it and you increases faster than its maximum speed. The photon simply never reaches you.

    If the universe were bent around on itself, we should be able to detect some form of curvature.  On Earth, if you trace out a large-enough triangle, you will detect "spherical excess": the sum of the angles in the triangle would be greater than 180 degrees. Of course, if you draw a very small triangle (covering only your garden, for example), you would be unable to measure this excess.

    When the latest attempt was made to measure any spherical excess (with the WMAP probe), we were unable to measure any excess. The Observable Universe appears geometrically "flat" -- meaning it shows no curvature. This COULD be because it has none (i.e., it is NOT bent onto istelf) or... it COULD be because our instruments are not precise enough to measure the very small excess we can detect over the size of our garden (the Observable Universe).

    In any case, light cannot make it "all the way around" and we are limited to our Observable Universe (13,800 million light-years in radius)

    -----

    **The number 13,800,000,000 (13,800 million) is called 13.8 billion in the USA and in a few other countries following the short-scale naming system for numbers.

    It is called 13.8 milliard elsewhere (long-scale naming system).

    https://en.wikipedia.org/wiki/Long_and_short_scale...

    The radius of the Observable Universe is in look-back distance (normally used in astronomy).  Of course, if we could see that far, we would see things as they were 13,800 million years ago, when the light left. Since then, the distance to that point has increased because of expansion so that its distance NOW would be a little over 40,000 million light-years in co-moving distance (used in cosmology).

  • Clem
    Lv 4
    2 months ago

    The known universe is light that we can see, i believe there is alot more universe on the other side of the know universe......... It would be dark with no sun or no neclear fusion...... So i dont believe light bends at all

  • Dixon
    Lv 7
    2 months ago

    If the universe is finite and geometrically curved like that (which it may not be), the main reason light wouldn't return to the same place is the expansion of space and the finite speed of light.

      

    Given the size of the current observable universe, it already contains locations on the path of a straight line that are receding from each other faster than the speed of light. Thus a light ray will never finish the  journey round the universe. Note that these locations are not traveling apart through spacetime faster than light. They are just so far apart that the new space that keeps turning up between things (ie expansion) makes them just *be* further apart. 

    This is difficult to visualise correctly because we have to impose a preferred reference frame to show what is happening, but space has no preferred reference frame.

    Also, Re Adam's answer and flatness. The description of "flat" is a specialist mathematical usage of the word, meaning that even over very large distances the three spatial x, y, z, coordinates behave exactly how you would naively expect. This is called a flat geometry. It doesn't actually mean flat like how everyone else uses the word :-)

  • 2 months ago

    "Some people and scientists" ? I doubt it. 

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