Because the universe is not infinitely old, the answer is number 3 listed above. We will find out shortly that we can actually estimate the age of our universe. There hasn't been enough time for the light to reach us from the most distant stars.The universe is finite, that is, it ends at some point.The solution to the paradox (why is the night sky dark?) could be due to several different possibilities:
Is there enough dust in the Universe to block our sight lines to some stars or galaxies? Yes, but if the Universe was infinite and with an infinite number of stars and galaxies, the light from those objects would heat up the dust causing it to glow brightly enough to light up the night sky.If every one of your sight lines ended on a galaxy, the night sky would be bright. Does it matter that we considered stars and not galaxies? No, because the same logic holds for galaxies.Even though this is obvious by simply looking at the sky, when you review the image of the Hubble Ultra Deep Field, there is clearly dark sky visible between every galaxy, providing further evidence that every sight line does not end on a luminous object.Ĭredit: Space Telescope Science Instituteīased on what you have learned so far, you may have a few questions. If the universe is infinite and filled with stars, the surface brightness of the night sky should be the same as the Sun's, so the night sky should be as bright as the daytime sky. There is an excellent public domain visualization of this phenomenon in the Wikimedia Commons it shows the sky randomly filling with more distant, and therefore fainter objects, but since the number of faint objects is so large, the picture of the sky eventually fills with a light of uniform brightness. If we picture spherical shells surrounding the Earth, though, the number of stars covering the surface area of one particular shell will increase by exactly the same amount as the brightness of the stars on that shell decreased, so the surface brightness, that is, the brightness per unit area on the sky, will be the same for every shell. You know from many discussions previously that every object appears fainter the more distant it is from Earth, and the brightness of that object drops off as 1/d 2, or an object twice as far away is 1/4th as bright. Let's briefly consider the mathematics of this situation. I made a pretty basic illustration of this, shown below: This means that if the universe is infinite and contains an infinite number of bright objects, the night sky will be bright! Since the night sky is dark, this tells us that one of our assumptions about the universe is incorrect. If this is true, then every sight line from the Earth will eventually intersect a bright object.
The reason that this question is so important is because its answer can tell us about the distribution of stars and galaxies in the universe.Ĭonsider the possibility that the universe is infinite and that it is filled with luminous objects (stars and the galaxies that contain them). Olbers), and it can be stated pretty simply: The question is usually called Olbers' Paradox, (after German astronomer Heinrich W. There is an old, simple question that can help us to understand a fundamental property of the universe.
0 kommentar(er)
