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Comment by laureny | Hacker News Reader

I don't see why the idea that "the universe might have been around forever" is so surprising since as far as I know, the prevalent theory is that time started at the big bang, which means that saying "before the big bang" makes as much sense as "going north while standing at the north pole".

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In this case forever doesn't refer to "all of time" but to "an unbounded past".

But that still isn't the same thing as "forever." Time does not go back infinitely — according to current theory, the universe definitely has a beginning in time.

The whole dimension-tautology has always irked me. Time, as a unit, is simply the "time" it takes for light to travel a certain distance. Distance, OTOH, is the "distance" it takes for light to travel under a certain amount of time. AFAIK one of the authors of this theory is a proponent of a variable speed of light. So if at some point in time light didn't move, then time didn't move, then that would mean that our universe existed since forever...? Not a physicist, but sometimes I feel weird when I am reminded of the fact that the Big Bang had a definite starting point 13.8B years ago (as you have done so), and then think about how time is really... a function of length and length is just a function of time.

> Time, as a unit, is simply the "time" it takes for light to travel a certain distance.

Without time there is no interaction between two atoms. There is no movement. It's not only about light traveling.

> The only reason for time is so that everything doesn't happen at once. -Albert Einstein

The Einstein quote is great. I would add: The only reason for time is so that everything can't be understood at once. 'Stretching' and 'scaling' as the foundational principle of distances and time makes the idea of a starting point needless. I wrote about it here: http://hashsign.co.uk/contemporary/by/thoughts/pop-pop-bang-...

>Time, as a unit, is simply the "time" it takes for light to travel a certain distance.

I believe that time is currently defined in terms of the period of a Cesium isotope.

No, time is defined in terms of atomic properties. It is not a function of length. (Length is, however, a function of time). A second is defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom.

A meter is defined in terms of the speed of light and the definition of a second. A meter is exactly the length of the path traveled by light in a vacuum during a time interval of 1/299,792,458 seconds.

Ah, thanks for that. I look pretty stupid now...I have actually heard of that definition but somehow I was thinking of time being ultimately defined by Planck units (time required for light to travel a Planck length).

People find comfort in knowing when something starts, and when something ends. It stems from controlling, wanting control over your environment. You can let that go though, and then the universe being infinite is beautiful.

If you posit that our universe is embedded in some higher space, it might still make sense to ask what's above the "north pole."

I think our best guess is that our universe is connected to other universes, perhaps through a larger bubble / body, and perhaps through that connecting through to perhaps infinite other universes.

> the prevalent [in the general public, and therefore in the scientific community] theory

The reason it's prevalent is because it is the most easily understood and acceptable by most people/religions/cultures - not because it is the most accurate or plausible explanation.

I don't think that's actually how the scientific community as a whole evaluates theories.

I'm not talking about the scientific community. I'm talking about people in the world. Christianity for example has accepted the Big Bang Theory as plausible and has not accepted others. This fact alone will help 70% of the world make a theory more prevalent.

Before the Big Bang theory, most Christian thinkers accepted the universe as eternal.

Citation, please. (Contra: Genesis 1:1.)

This is an anecdotal reposnse mostly based on having grown up in a strongly charismatic Christian background, but the folks I knew probably would have said that god existed forever and the universe started when he made it.

Obviously that's going to depend on who you ask in the denomination and what denomination you ask. My experience is that you're not generally going to get a very nuanced view of space and time but occasionally you'll be a little surprised.

Again. Anecdotal. Ymmv

Genesis 1:1 does not reflect the thought of any Christian thinkers.

Christianity is a rather broad grouping that encompasses a hundred churches with different beliefs. I don't think you can make meaningful statements about what Christians believe, except that they believe in Christ (hence the name). There's no central planning committee that decides what to believe.

For practical purposes, you may as well just use the word religion, as in "Religion for example has accepted the Big Bang Theory", which is more obviously too general.

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