Big Bang leads to a ‘multiverse’ of questions

For much of our history, we have conceived the universe as something eternal, in which everything we know of comes and goes. Then, in the first half of the 20th Century Georges Lemaitre, a Roman Catholic priest and a brilliant physicist, proposed the known-to-be expanding universe points back to a time when everything was concentrated in one lump.

He called this the “primaeval atom.” This then started to expand, leading to the universe we have around us today.

Einstein disagreed, although his calculations proved Lemaitre right, and eminent astrophysicist Fred Hoyle, would not accept the idea of a beginning, and came up with the derisive term: “These men with their Big Bang.” The name stuck, although not in the way Hoyle expected. The fading breath of the Big Bang has since been detected, mapped and studied. The universe is expanding, and the young universe was different from what exists today. There was a beginning, and probably will be an end.

An early possible answer to both these questions came from the “Big Crunch Theory.” If everything is gravitationally pulling at everything else in the universe, we would expect the expansion we see to gradually slow, and possibly stop. Then everything would start falling inward again until at some point in the far future there would be a “Big Crunch,” with everything back in one compact lump, a repeat of Lemaitre’s primaeval atom. Then, at some point this would undergo a Big Bang, and the whole universal process would start over again. This provided a very convenient answer to the questions as to what came before, and what comes after: one universe after another.

Unfortunately, this convenient idea was ruled out by our subsequent observation that the expansion of the universe is not slowing towards a new big crunch. The expansion is accelerating. This suggests the universe will expand, becoming more and more rarefied, with all the stars eventually running out of fuel. At some point the particles making up the atoms of our stars, worlds, and us, will decay, and everything will finally fade away. Would a better understanding of the beginning of the universe help us here?

Unfortunately, as yet that part of our universe’s history is unobservable.

Until about 380,000 years after the Big Bang, the universe was an incredibly hot, dense, glowing fog.

At the moment we can only work our way further back towards the beginning through calculation.

However, our knowledge of physics has been derived under the conditions we see around us now, or produce in the laboratory. This does not help us understand the extreme conditions after the Big Bang.

An idea currently enjoying a lot of interest is the existence of an eternal (?) “multiverse,” in which universes form, expand and dissipate, like bubbles in a “cosmic foam.”

Apart from making imaginative calculations, is there something concrete we can do to establish whether this foam exists?

It has been suggested that in foams, bubbles are often in contact with other bubbles. At these contact surfaces, the curvature is different, as we see when taking a bath with lots of bubbles.

We might be able to see the contact faces with other universes by searching the sky for patches of sky that are different.

The most distant region of space we can see is the cosmic microwave background, that point 380,000 years after the beginning when the fog cleared. The search is on for unusual patches in that. Nothing has been found yet.

Of course, invoking a multiverse in which universes like ours form, expand and then dissipate is only pushing the big question back another level.

Did the multiverse have a beginning, or is it eternal? Can we answer that?

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Venus lies extremely low in the dawn glow. Jupiter shines low in the west after sunset. The Moon will reach First Quarter on the 15th.

Ken Tapping is an astronomer with the National Research Council’s Dominion Radio

Astrophysical Observatory in Penticton.