![]() ![]() Now if we imagine the light bulb moving quickly away from us, it’s giving out the same light but it’s doing it over a larger distance in the same amount of time. Now, if you could slow down time and watch how the wave of light being emitted from the stationary light bulb forms, you would see a steady chain of waves forming with all the individual waves the same length as each other and steadily moving away from the object. So we have a light bulb sat there giving out one wave of light per second. This light is forming continuously so we can also say that it takes one second for the wave to be completely formed. Let’s imagine an object, a light bulb perhaps, and this light bulb gives out an imaginary amount of light per second- for ease, let’s say one wave of light per second. For the benefit of any of you reading that are interested, here’s a quick explanation of Doppler shifting- alternatively, jump past the italic paragraphs! It is widely accepted that space, and indeed everything within it, is moving away from us and it’s doing that really quite quickly! When an object is giving off light it causes this light to become ‘red shifted’ according to the Doppler effect. Red shifted to the invisible – The principle behind this explanation lies in the expansion of space. As stars are born and die, the points of light change but the brightness of the sky stays constant. Therefore, there shouldn’t actually be an infinite number of stars in the sky. When we look at the night sky, we aren’t seeing everything, we’re seeing a snapshot in time. The infinite versus the finite – A major argument being made about this paradox is the finite nature of a star’s life cycle. The next two explanations are the truly controversial explanations- both have arguments for and against: The main problem with this suggestion is, the light falling on the dust would eventually heat it up and that too would start glowing- so we can’t really accept that as our explanation! The dusty darkness – One explanation that has been proposed is that light is absorbed by the massive amounts of dust that lie between us and those far off stars. Here are a few that have stood up to questioning better than others: Throughout the 190 years since it was first posed, there have been many attempts to answer the paradox. So why don’t we see these stars? Surely if there was a star at every point in the night sky, the sky would be as bright as day? This star is likely to have roughly the same brightness as our own star. The paradox begins by asserting we see stars all around us, current theory suggests that space is infinite and as such you can (sort of) say that if you look out in any direction far enough, you will eventually see a star. So, what is it that makes this such a controversial and hard to answer question? A quick search will reveal the idea of a paradox, first set out by a German physicist- Heinrich Wilhelm Olbers in 1823. Image credit: Kmarinas86 via the Wikimedia Commons If all lines of sight end in a star, should the sky not look like this all the time? (If the animation isn’t working, try clicking on the image!) ![]()
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