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How Big Is The Universe?

The Universe 590 million years after the Big Bang. Credit: Alvaro Orsi, Institute for Computational Cosmology, Durham University.

The Universe 590 million years after the Big Bang. Credit: Alvaro Orsi, Institute for Computational Cosmology, Durham University.

Recent measurements reveal that the Universe is at least 150 billion light-years in diameter. For comparison, its age is estimated to be about 13.7 billion years. Doesn’t make sense does it?

Since some of you may be wondering what kind of disparity we’re talking about, let me elaborate. You see, to arrive at that age, scientists had to measure light (or electromagnetic radiation) coming from the outermost borders of the Universe. This radiation, specifically known as the cosmic microwave background radiation is a throwback to the youngest years of the Universe. So if it had to take 13.7 billion years for light coming from the outermost regions to reach us, then we should be expecting a diameter within that order of magnitude. Simply put, around twice that value or 27.4 billion light-years. But lo and behold, we’re seeing a number much much larger than that.

This value, however, only makes sense if our Universe’s size were constant. Studies have shown that that isn’t the case. In fact, separate observations have shown that the Universe is actually expanding. To top it all, it is confirmed that it does so at an accelerated rate.

Lets make a very simplified analogy, just to give us a rough idea regarding the source of discrepancy. Imagine yourself having a friend standing on a planet at the outermost galaxy. Lets also assume you both have superhuman strength and are able to play catch with indestructible balls (whose constant speed you both know) that takes a straight path, and that no obstruction exists along the said path.

If he throws a ball, you’d be able to determine either the time of flight or the distance traveled if you knew the other physical quantity. Thus, if the time of flight is 13.7 billion years and the ball was traveling at the speed of light, neglecting relativistic effects, the distance should be 13.7 billion light-years.

But what if your friend is moving towards or away from you? We would have to make certain adjustments. You would still be able to measure the said physical quantities if he were made to throw a good number of balls at regular intervals and if you made some adjustments to your equation, taking into consideration the relative velocities involved.

After the first throw, if your friend is moving away, the distance between you and him would be greater than 13.7 billion years. Even greater distances can be achieved if he were moving away at increasing velocities.

Here are two related articles from Universe Today:

NASA also has some:

Tired eyes? Let your ears help you learn for a change. Here are some episodes from Astronomy Cast that just might suit your taste:

Sources: NASA WMAP, NASA Ask an Astrophysicist

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