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I am sure this is a silly question, but I was reading something that described the pre big-bang universe as having "nearly infinite mass."

How can something be "nearly" infinite? The term seems to make no sense.

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    $\begingroup$ Anything before the big bang is highly speculative, and talking about the total mass of the universe is pretty nonsensical, but usually, when you say something is "nearly infinite", what you mean is that the quantity is so much larger than all of the relevant physical parameters, its finite value can be ignored, and we need only consider the "small" masses--for instance, we don't factor the recoil of the Earth when we solve simple projectile motion problems. We pretend that the Earth's mass is "nearly infinity". $\endgroup$
    – Zo the Relativist
    Commented Jun 22, 2012 at 3:37
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    $\begingroup$ @Jerry: I like your interpretation. i.e. "nearly infinite" means "finite but big enough to ignore" or, alternatively, "negligibly large". $\endgroup$
    – Warrick
    Commented Jun 22, 2012 at 8:44

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Any natural number, no matter how large, is "infinitely far away" from infinity, i.e., there are an infinity of numbers larger. So, your intuition is correct. "Nearly infinite" seems very odd indeed.

Of course, "pre big-bang universe" sounds suspicious too as does the notion that whatever that was has the property of mass.

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It sounds like the article is not credible. They could have easily used "Had a mass approaching infinity". Which would mean a non-static ever increasing mass. I suggest seeking reading material that is properly referenced and supported with mathematically rigorous explanations.

Anyone can post opinionated "ideas", but without proper references all it is is wild conjecture.

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The universe seems to be well described by a solution to Einsteins equation called the FLRW metric. If you extrapolate this backwards towards the Big Bang the density of matter increases, and at the Big Bang itself the density becomes infinite.

A quick side note: the universe may well be of infinite size, so it's mass is necessarily infinite. It only makes sense to talk about the density i.e. the amount of matter in some chosen volume.

Anyhow, few believe that the density actually becomes infinite. It's widely believed that quantum gravity, or something like it, intervenes as we approach the moment of the Big Bang. I'd guess that the article you've read means that the density becomes extraordinarily large as we approach the Big Bang, but never becomes infinite. Hence the description "nearly infinite". However I agree with the other answers that the phrase "nearly infinite" is meaningless outside of a metaphor.

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  • $\begingroup$ I think the phrase "infinite size", like the presence of an infinity in any physics equation, is a flag to "check your premises". In this case, I think it means to closely examine the notion of "size" as applied to the concept of "universe". The same check should be applied to the notion of mass. Mass is not a property of the universe; mass is a property of entities in the universe. $\endgroup$
    – Alfred Centauri
    Commented Jun 22, 2012 at 12:32

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