For each part, say whether the statement is sensible or not. Give a one or two s
ID: 120253 • Letter: F
Question
For each part, say whether the statement is sensible or not. Give a one or two sentence explanation on why or why not.
(a) We see distant galaxies as they were when the Universe was younger and, if there are people living in those galaxies today, they would see the Milky Way as it was when the Universe was younger.
(b) The main reason that the night sky is dark is that stars are generally so far away.
(c) Strange as it may sound, most of both the mass and energy in the universe may take forms that we are unable to detect directly.
Explanation / Answer
(a) Yes. The reason for why we see distant galaxies in the youth full stage of universe is because of huge distance between them and us. It takes millions of light years to travel to these galaxies and when we see these galaxies, in reality we are observing the light that has travelled millions of light years ago thus presenting a younger version of Universe in comparison to the present. Hence when any inhabitant of these galaxies observe us they will find a younger version of earth and universe. Since the distance between them and us is the same and light has to travel the same light years (unless of course, they have advanced way of observation which is faster than the speed of light).
(b) The night sky is dark because due to the earth rotation, for approximately 12 hours’ earth will not be facing the sun, the only star that provides us sufficient light energy. Suppose if you consider the earth is proximate to another star (and facing that star during the other half of the rotation) which would supplement the light during the 12-hour night time, there wouldn’t be any dark night sky. Since all our close star are quite distant, we can observe a beautiful dark night sky.
(c) Scientists has studied the total observed mass and energy of the universe and interestingly their calculations suggested that there may be major amount of mass and energy or so called ‘dark matter’ in the universe, for the mass balance. But unfortunately this mass cannot be detected by the existing astrophysical methods and measurements, since they don’t respond to existing measurement methodologies. They are neither providing any positive or negative readings in our measurement scales. Therefore, indirect methods need to developed to identify and quantify these features. A simple example is the presence of black holes, extremely strong gravitational field that can even swallow the light. Since even the light is absorbed is impossible to estimate the dimensions of the black holes, but are indirectly observed when the illuminating matter is being absorbed in the black hole area. Simply put the majority of the mass and energy in the universe is beyond our direct physical estimation.
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