If the universe is only 13.8 billion years old, and nothing can travel faster than the speed of light (1 lightyear per year), how can the observable universe possibly be nearly 100 billion lightyears across? How do we reconcile the sheer size of the universe with the understanding that it all emerged from an infinitely dense point not so long ago?
In: Physics
Nothing can move *through* space faster than the speed of light, but the space *between* sufficiently distant objects can increase rapidly enough that light emitted from them *right now* will never be able to traverse the distance, and the farther apart they are the more rapidly the space will grow. The overall rate of expansion has also been accelerating over the past few billion years, and this is expected to continue forever.
The entire universe also did not emerge from one infinitely dense point. The observable universe was contained with a very tiny volume, but it wasn’t infinitely small, and entire universe was still far larger than this, and may possibly be infinite. At some point shortly after the big bang, the universe entered a brief “inflationary” period where its size increased drastically before returning to normal expansion.
All of these factors lead to the universe being much larger than one would think based on the speed of light alone.
The universe is as large as it ever was or ever will be. When people say the universe is expanding, what that equates to is that it is decreasing in density. The initial singularity before the so called big bang would have been just as infinite, though likely in a different sense/mechanism, as the current universe is apparently infinite now.
Rate of expansion of universe is not bounded by the speed of light.
Another way to put it is nothing can travel faster than the speed of light inside the universe but the space inside the universe can stretch much faster; there doesn’t seem to be a limit on that.
Incase it’s still not clear, let me try another analogy albeit not completely accurate but its easier to understand. Imagine a slightly inflated balloon. Put two points A and B on that balloon and imagine an ant standing on point A. Now imagine the ant is the photon of light and balloon is its universe. Now lets say the ant can only travel at constant maximum speed of 9 meter per hour towards point B i.e nothing on that balloon surface can travel faster than 9m/hr. Now when the ant starts to move towards point B, you start inflating the balloon. In this case the ant has more distance to cover to get to point B. If you keep inflating the balloon faster and faster than eventually the ant will never reach point B as the balloon surface will be increasing faster than Ant’s speed of 9m/hr. Our universe expanded in a similar fashion. And as we chat, the distance between most galaxies are increasing due to mysterious dark energy and eventually we won’t be able to see other galaxies because light from those galaxies will never be able to reach us; also we will be long dead by then (sad face). Hope this makes it clear.
because it is constantly expanding outward. and this has been happening in every direction from the origination of the big bang.
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