Science fiction has come up with countless ideas for weird forms of life not based on boring old DNA, or even on matter as we know it.

There’s Stanislaw Lem’s sentient ocean in Solaris, or the neutron star civilization made of nuclear matter in Robert L Forward’s Dragon’s Egg.

Oh, and here’s an extra crazy one - life composed of cosmic strings and magnetic monopoles, evolving in the hearts of stars.

Oh, wait a minute - that last one is an actual scientific proposal.

Scientists can sometimes be a little carbon-chauvanistic when we imagine other possible life forms.

Which is understandable - carbon-based chemistry enables the most complex structures that we know of in this universe.

But could some other mechanism exist that could allow the incredible chemical diversity needed to power life?

Well, not that we know of.

But that hasn’t stopped some scientists from looking.

One of the most bizarre proposals for life not as we know it doesn’t even use atoms.

It proposes that fundamental kinks and defects in the fabric of the universe - cosmic strings beaded with magnetic monopoles - may evolve into complex structures, and even life, within stars.

This idea was just published in Letters High Energy Physics Letters by physicists Luis Anchordoqui and Eugene Chudnovsky, and today on Space Time Journal Club we’re going to see how legit this idea actually is.

But first we need to go through some of the basics.

What exactly are cosmic strings and magnetic monopoles?

Both of these are fascinating subjects well overdue for their own episodes, so I’ll keep in brief here.

Cosmic strings and magnetic monopoles are what we call topological defects.

The best way to describe topological defects is with some examples.

Imagine a fur rug in which you can brush the fur to lie in whatever direction you like.

If the fur is pushed to the left at one end and the right at the other end, then somewhere in between there must be a transition between the two states.

There’s no way for that transition to be smooth, so you have this line.

You can move the line around by brushing the rug left or right, but you can’t get rid of it without brushing the entire rug in one direction.

You could also get a topological defect if you tried to brush the rug into a spiral.

The transition between all points would be smooth, with the grain changing angle only slightly.

But at the eye of the spiral you’d have a non-smooth transition.

And that’s the common feature of a topological defect - a sudden change in the “grain” of some space that can’t easily be disentangled.

You can have exactly the same thing in magnetic materials, where the direction of the poles of the little magnetic particles changes across the substance.

Topological defects are also found in crystals.

They form during the phase transition from liquid to solid.

That crystallization can begin in different places in the liquid.

And these lattice regions spread and join until you have a single crystal, but if those initial regions didn’t all line up in the same way then you have defects where the regions meet each other.

Quantum fields should also be able to develop topological defects.

These may have been formed soon after the Big Bang when massive phase transitions swept across the universe.

These transitions were analogous to the phase transitions between states of matter - for example, water freezing into ice.

But here, the quantum fields themselves changed state due to the rapidly dropping temperature.

The technical term is “spontaneous symmetry breaking” - the same events that led to the appearance of the separate forces from an initial unified force.

We’ll be discussing that more in the future, but for now the important thing is that these phase transitions could have resulted in different types of topological defects, just like when crystals form.

Let’s go through the possibilities: a 0-dimensional topological defect is a magnetic monopole - like the north or south pole of a bar magnet that somehow lost its counterpart.

A 1-D topological defect is a cosmic string - an extremely thin filament.

2-D defects are called domain walls - they’re the boundaries between regions of the universe with different properties - for example, different vacuum energies.

We’re interested in the strings and monopoles for now.

In certain theoretical scenarios, a monopole can be connected to the end of a string - or two strings, actually.

Such monopoles are called beads.

And you can have a chain of beads - a necklace.. Anchordoqui and Chudnovsky imagine a type of nuclear life, in which these chains form complex structures that can have a sort of chemistry - possibly even evolving into what we might call life.

The goal of their study was to figure out under what circumstances this might happen.

The authors lay out three conditions for life that they investigate.

Let’s go through them.

Condition 1) The ability to encode information.

Fair enough - our DNA encodes all the instructions our cells need to build the molecular machinery of life.

It’s hard to imagine a life form that didn’t have a way to store information.

Condition 2) The ability of information carriers to replicate faster than they disintegrate.

Again, straight forward - any given chain of molecules holds information, but it isn’t much good if it falls apart before it reproduces itself.

And 3) a source of free energy.

This is something we know is essential for any life, including nuclear life.

Let’s go through each of these conditions in detail.

Can these string-monopole necklaces store information?

Well, in DNA there are 4 different base pairs and the ordering of those base pairs is a language - it dictates the order of amino acids transcribed into proteins.

With simple magnetic monopoles, the only possible necklace is an alternating series of north and south poles - or poles and anti-poles.

There’s only one possible configuration, and so there’s no way to store information that way.

But if you add slightly more exotic physics you can form different types of monopole.

For example, there’s this scenario in this early universe symmetry-breaking stuff where, after the monopoles form, they split in two - into so-called semi-poles.

There are four types of seminole - two for each of the original monopole type.

Four coding “letters” - sounds a bit like DNA.

Semipoles have an added bonus: whereas monopoles and anti-monopoles will always attract each other and annihilate if they come together.

With semipoles, it’s possible to form string segments capped by NON-annihilating semipole pairs that actually repel each other.

In this way, it may be possible to develop complex string structures, analogous to chemistry.

And maybe you can even build something like DNA.

OK, moving on to life condition number 2: can these information carriers replicate faster than they can disintegrate?

These necklaces are probably not too stable - but that’s OK as long you can replicate them faster than they fall apart.

And this is where stars come in.

Others have speculated that cosmic strings may get trapped inside stars in the process of star formation.

Those stellar interiors might then provide the mechanism for necklaces to rapidly change and even replicate.

Depending on the stellar type and region, the insides of stars can be very turbulent places.

Flowing plasma and magnetic fields may stretch and break necklaces, which could reconfigure them over and over until they find a state that is stable in the environment, combined with developing the ability to replicate faster than they are torn apart.

As for how that replication happens - well the study doesn’t go into detail, except to say that it might be catalyzed by interactions with atomic nuclei in the star.

Perhaps nuclei somehow help necklaces build a parallel chain of beads, that then peels off as an identical necklace, similar to how RNA reproduces.

And finally, life condition number 3: do we have a source of free energy?

By free energy, I don’t mean energy that you don’t have to pay for.

I mean energy that is available for use, in a thermodynamic sense.

Energy can only be used to do work if there exists differences in the amount of energy in different possible states.

If energy is concentrated in certain places we would call that an ordered, low entropy situation.

Energy likes to spread itself out as evenly as possible, moving towards disordered, high-entropy states.

It’s possible to use energy as it flows between different states in this process, like putting a water wheel in a flowing river.

For example, life uses the energy flowing from the high energy-density of the Sun to the lower energy density of the Earth.

In fact we talked about all of that in our episode on the physics of life.

We saw that these temporary increases in order, represented by life, actually speed up the process of smoothing out all of the energy.

Little low-entropy blips like life ultimately accelerate the increase in entropy of the universe.

OK, so inside a star there’s definitely free energy.

Energy flows from the fusion engine in the core to the surface.

It’s conceivable that a lifeform could harness that flow.

Well what would that look like?

Well, it would have to hasten the spreading out of energy.

Energy could be spread more evenly across the electromagnetic spectrum, which would look like cooling - the star might appear cooler than it should.

Or perhaps the nuclear reactions in the core proceed faster, hastening the dissipation of the star’s energy through space.

At any rate, the star should behave differently to what our stellar physics models predict.

There are a few stars in our modern surveys that don’t quite act as they should, however there are many other possible explanations and it might be a little premature to claim discovery of a new lifeform.

We’re going to have to get a much better understanding of cosmic strings and monopoles - and, you know, actually verify that they exist in the first place - before we can decide whether they can interact with the complexity needed to evolve into life.

And the authors of this paper are not pretending that any of this is likely - their point is more to show that other possible bases for life might exist, beyond the familiar carbon chemistry.

So are the stars filled with thriving ecosystems of critters built from fractured quantum fields?

Not likely, but not yet impossible.

And who knows what other bizarre life forms may be waiting to be discovered, in distant, stranger parts of space time.