I've given this a lot of thought the last couple days. I look at the Hubble equation [itex]v=H_0 d[/itex], and I don't see how this necessitates everything existing in a single point at some time in the past. Certainly, everything was really close together 13.7 billion years ago, but not in an infinitely small volume.(adsbygoogle = window.adsbygoogle || []).push({});

[itex]1/H_0[/itex] (Hubble constant is in km/s/Mpc) does not give you the age of the universe (assuming the Hubble constant is constant through time). It gives you the amount of time it takes to travel a Megaparsec going at [itex]H_0[/itex] km/s. If you calculate the amount of time it takes to travel a Megaparsec going 71 km/s, it is indeed around 13.78 billion years. However, any object currently a Megaparsec from the Earth was not always receding at 71 km/s relative to the Earth, as you can see from the Hubble equation. As you go back in time and the object gets closer to the Earth, the velocity decreases. The way I see it, d=0 acts like an asymptote. The object approaches Earth the further back in time you go, but the distance is always non-zero, no matter how far back you go.

Another way to look at it is to see what happens when you apply the case of everything existing in a single point to the Hubble equation. The distance between any object is 0, so the velocity is also 0. If the velocity is 0, nothing moves, and the distance remains 0 for all time. Nothing ever expands! Something magical must have happened for these objects to separate before the expanding could begin.

It seems more logical to conclude that the universe has been expanding for an infinite amount of time. It's just that before 13.7 billion years ago, everything was so condensed that matter could not exist as we know it exists now.

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# Why are we so sure the universe existed in a point 13.7 billion years ago?

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