Brian Greene answers 10 mind-bending questions about our Universe

Renowned US theoretical physicist Professor Brian Greene is giving a talk at Auckland's Q Theatre on April 5. Image / Think Inc

What’s outside the Universe? Does dark matter exist? What are the prospects of finding other intelligent life? And can scientists really find a “theory of everything”? Science reporter Jamie Morton put 10 mind-bending questions to New Zealand-bound US theoretical physicist, Professor Brian Greene.

There are scientific efforts like Search for Extraterrestrial Intelligence (SETI) dedicated to finding inhabitants of other planets. Yet, as has been discussed in studies, are advanced civilisations like ours more likely to self-destruct before they can make contact with one another?

Well, I certainly hope not.

But it’s a real concern, because our one example, here on planet Earth, suggests that technological development goes hand-in-hand with the development of advanced weaponry - and an increasingly aggressive attitude toward control over territory.

If that’s a pattern that plays out in other planets, assuming that those planets are home to other advanced civilisations, then that’s a real possibility.

But I’m an optimist, and I’d like to imagine that our brains will catch up with our technology, and we’ll stop doing stupid things, so self-destruction would be one of the possibilities that would hopefully drop away.

With Nasa’s ongoing exploration of exoplanets, we often hear of the possibility of finding “other” Earths. But what’s the probability of actually finding a life-supporting planet with a biome not completely hostile to our own biology?

You know, it’s hard to give an actual number, like 13 per cent or something that that specificity.

But we have one example of a biosphere that supports life, and clearly that biosphere is conducive to our existence.

In fact, it’s why we exist in the first place.

Is it conceivable that there are other biomes out there that align with the chemical make-up of ours? Sure.

There’s nothing particularly unusual about what we have here on planet Earth: it’s just a blend of oxygen and nitrogen and trace amounts of other gases.

On a planet that’s a reasonable distance from a star - allowing for the existence of liquid water – these things are not highly different.

So I think it’s quite likely that, as we search exoplanets, we’re going to find some that we’d imagine would be compatible with our existence.

Another question you’ve no doubt been asked plenty of times: is time travel possible in any form, such as “wormholes” connecting distant parts of the universe?

Time travel to the future is possible, but I don’t mean the silly version of it, where we’re older.

If we do want to see what planet Earth is like, say, one million years from now, Albert Einstein gave us a strategy for how to do it, 100 years ago.

Say you go out into space and travel near the speed of light in a fast-moving rocket.

"Time travel" might be theoretically possible - just not like we see in Hollywood movies like Back to the Future.

It might only take six months to go out and another six months to come back – but depending how close you got to light-speed, once you step out of your ship it might be a million, billion or trillion years into the future.

This is not controversial: it’s how time works, according to special relativity.

I think the question that people are most intrigued by is travelling back in time, and that’s a big unknown.

Wormholes potentially provide a way of doing that, and there are other strategies, but these are very speculative ideas.

We don’t even know if there are wormholes, or if the other ingredients for travelling to the past that people hypothesise actually exist.

So, is time travel to the future possible? Absolutely.

To the past? That’s a big question mark.

We talk of the “observable” Universe. What’s outside it?

We think that outside the observable universe is just more universe – pretty much like the universe that we can observe.

I mean, the observable universe is simply defined by how far out we can see, by virtue of how long light has been in transit since the Big Bang.

We can’t see anything that’s too far away, because the light that is emitted will not have had enough time to traverse the wide separation between us as yet.

But the observable universe gets bigger by one “light day” each day - so every day, you can see one light day further.

And as far as we can tell, it’s not as though the universe, as we see more of it, is substantially different from the universe that we have seen.

So, the anticipation is that it’s more of the same.

We also hear much about the idea of a “multiverse” - or a hypothetical group of multiple universes that supposedly comprise everything that exists. Is it possible we’re living in one of many universes?

It’s certainly possible that we’re living in a multiverse.

This idea comes from many strands of theoretical physics, from quantum mechanics to cosmology.

Michelle Yeoh in the film Everything Everywhere All at Once, which explores the notion of multiple realities.

And we’ve seen a recent uptick in Hollywood’s interest in the multiverse, which, while not scientifically accurate, certainly captures some of the essential ideas.

Could it be that there are other realms, or other realities, that are similar to ours, but not identically the same?

According to fundamental physics, it’s worth thinking about: but we should also emphasise that there’s no evidence for it as yet, whatsoever.

Here’s one that I know you’re fairly rehearsed in answering: what came “before” the Universe?

It’s hard to say what came before the Universe, in the sense of, what was before the Big Bang.

It could be that the idea of “before” the Big Bang is actually meaningless, because time itself may have come into existence with the Big Bang.

The observable universe is defined by how far out we can see, by virtue of how long light has been in transit since the Big Bang. Photo / NZME

So, the notion of “before” may be a word that seems to make sense, but just doesn’t apply.

Another possibility, though, is the Big Bang is not the beginning of time, and that a long stretch of time may have existed well before it... maybe infinitely far back.

If that’s the case, the Big Bang would simply be an interesting event that created our little realm of reality, but sits within a much larger expanse that pre-dated our existence.

The logical follow-up to that question: how and when does our Universe end?

It seems most likely that the universe will end when all of its complex structures - stars, galaxies, people, black holes - all disintegrate into their constituent particles, that then just waft through an ever larger, ever colder, cosmos.

And we anticipate that will happen in the future, probably about 10 to the 100 years from now.

That’s an enormous duration of time, given we’re currently 10 to the 10 years since the Big Bang, so it’s not something to worry about in any sense.

But for a long stretch of time, we human beings didn’t exist.

And for a long stretch of time, after the Earth and the Sun and all of us are gone, the universe will persist, again in a quiescent dark state.

We’re just a brief blip on the cosmological timeline.

It’s thought to account for approximately 85 per cent of the matter in the universe, but how sure can we be that dark matter really exists?

We don’t know if dark matter exists.

Since the 1930s, there’s been circumstantial evidence pointing toward dark matter.

Our observations of the motions of stars and galaxies suggests that the movement we observe couldn’t happen unless there is more stuff out there that we don’t see.

And that’s what the dark matter is, it’s matter that we believe is out there, but doesn’t give off light and isn’t visible.

But the more we’ve searched for dark matter, and tried to capture it directly, the more frustrated we’ve become, because we’ve yet to actually capture and have direct evidence of it.

That’s led some people to suggest other explanations for the observations of stars and galaxies, which don’t use dark matter.

I still believe that yes, dark matter does exist: but until we find it, capture it and measure it, I won’t be convinced and nor should anybody else.

One intriguing notion, as we heard from Professor Stephen Hawking shortly before he died in 2018, is that black holes have “soft hair”. Under the “no-hair theorem”, black holes supposedly lack any observable features beyond their total mass, spin and charge - or have “no hair”. Hawking and colleagues have instead suggested that black holes, rather, have “soft hair” - or low-energy quantum excitations that release information when they evaporate. That might go some way to addressing the “information paradox” of black holes supposedly fading away to nothing, versus quantum mechanics asserting that information can never be lost. What’s your view on this?

Yes, black holes probably do have “soft hair”.

The work that we’ve been doing in string theory, which puts together gravity and quantum physics, suggests strongly that there are subtle attributes of black holes that were not captured by the most early theoretical investigations.

Astronomers at the Event Horizon Telescope revealed this image of supermassive black hole Sagittarius A last year. Photo / National Science Foundation

These only focused upon the mass of a black hole, the electric charge of a black hole, or the spin or rotational speed of a black hole.

But we’ve been long puzzled, and recent work is suggesting that there are more subtle features that emerge from a careful application of quantum ideas to black holes.

One final question: will scientists ever find an all-encompassing “Theory of Everything”?

If that “everything” is the fundamental ingredients to particles and all fundamental mathematical laws, then yes, I do think that one day we’ll have an all-encompassing theory.

But some people want to go further: by “everything”, they mean life or consciousness, and all of these questions.

Certainly, these are beyond what we talk about when we discuss a unifying Theory of Everything.

Will we ever understand those other things one day? I think we will.

But every time we understand something more, it just opens up more questions.

Professor Brian Greene will be appearing at Auckland’s Q Rangatira Theatre on Wednesday, April 5, where he’ll answer some of the most challenging and existential questions of our time, and share insights from his latest book, Until the End of Time: Mind, Matter, and Our Search for Meaning in an Evolving Universe. Tickets can be booked online at www.thinkinc.org.au/greene.