Saturday, July 31, 2021

Are we made of math? Is math real?

[This is a transcript of the video embedded below.]

There’s a lot of mathematics in physics, as you have undoubtedly noticed. But what’s the difference between the math that we use to describe nature and nature itself? Is there any difference? Or could it be that they’re just the same thing, that everything *is math? That’s what we’ll talk about today.

I noticed in the comments to my earlier video about complex numbers that many people said oh, numbers are not real. But of course numbers are real.

Here’s why. You probably think I am “real”. Why? Because the hypothesis that I am a human being standing in front of a green screen trying to remember that the “h” in “human” isn’t silent explains your observations. And it explains your observations better than any other hypothesis, for example, that I’m computer generated, in which case I’d probably be better looking, or that I’m a hallucination, in which case your sub consciousness speaks German und das macht igendwie keinen Sinn oder?

We use the same notion of “reality” in physics, that something is real because it’s a good explanation for our observations. I am not trying to tell you that this is The Right Way to define reality, it’s just for all I can tell how we use the word. We can’t actually see elementary particles, like the Higgs-boson, with our own eyes. We say they are real because certain mathematical structures that we have come up with describe our observations. Same thing with gravitational waves, or black holes, or the particle spin.

And numbers are just like that. Of course we don’t see numbers as objects walking around, but as attributes of objects, like the spin that is a property of certain particles, not a thing in and by itself. If you see three apples, three describes what you see, therefore it’s real. Again, if that is not a notion of reality you want to use, that’s totally okay, but then I challenge you to come up with a different notion that is consistent and agrees with how most people actually use the word.

Interestingly enough, not all numbers are real. The example I just gave was for integers. But if you look at all numbers with infinitely many digits after the decimal point we don’t actually need all those digits to describe observations, because we cannot measure anything with infinite accuracy. In reality we only ever need a finite number of digits. Now, all these numbers with infinitely many digits are called the real numbers. Which means, odd as it may sound, we don’t know whether the real numbers are, erm, real.

But of course physics is more difficult than just number. For all we currently know, everything in the universe is made of 25 particles, held together by four fundamental forces: gravity, the electromagnetic force, and the strong and weak nuclear force. Those particles and their forces can be mathematically described by Einstein’s Theory of General Relativity and Quantum Field Theory, theories which have been remarkably successful in explaining what we observe.

For what the science is concerned, I’d say that’s it. But people often ask me things like “what is space-time?” “what is a particle?” And I don’t know what to do with questions like this.

Space-time is a mathematical structure that we use in our theories. This mathematical structure is defined by its properties. Space-time is a differentiable manifold with Lorentzian signature, it has a distance measure, it has curvature, and so on. It’s a math thing. We call it “real” because it correctly describes our observations.

It’s a similar story for the particles. A particle is a vector in a Hilbert space that transforms under certain irreducible representations of the Poincare group. That’s the best answer we have to the question what a particle is. Again we call those particles “real” because they correctly describe what we observe.

So when physicists say that space-time is real or the Higgs-boson is real, they mean that a certain mathematical structure correctly describes observations. But many people seem to find this unsatisfactory. Now that may partly be because they’re looking for a simple answer and there just isn’t one. But I think there’s another reason, it’s that they intuitively think there must be something more to space-time and matter, something that distinguishes the math from the physics. Something that makes the math real or, as Stephen Hawking put it “Breathes fire into the equations”.

But those mathematical structures in our theories already describe all our observations. This means just going by the evidence, you don’t need anything more. It’s therefore possible that reality actually is math, that there is no distinction between them. This idea is not in conflict with any observation. The origin of this idea goes all the way back to Plato, which is why it’s often called Platonism, though Plato thought that the ideal mathematical forms are somehow beyond human recognition. The idea has more recently been given a modern formulation by Max Tegmark who called it the Mathematical Universe Hypothesis.

Tegmark’s hypothesis is actually more, shall we say, grandiose. He doesn’t just claim that actually reality is math but that all math is real. Not just the math that we use in the theories that describe our observations, but all of it. The exponential function, Mandelbrot sets, the number 18, they’re all real as you and I. If you believe Tegmark.

But should you believe Tegmark? Well, as we have seen earlier, the justification we have for calling some mathematical structures real is that they describe what we observe. This means we have no rationale for talking about the reality of mathematics that does not describe what we observe, therefore the mathematical universe hypothesis isn’t scientific. This is generally the case for all types of the multiverse. The physicists who believe in this argue that unobservable universes are real because they are in their math. But just because you have math for something doesn’t mean it’s real. You can just assume it’s real, but this is unnecessary to describe what we observe and therefore unscientific.

Let me be clear that this doesn’t mean it’s wrong. It isn’t wrong to say the exponential function exists, or there are infinitely many other universes that we can’t see. It’s just that this is a belief-based statement, not supported by evidence. What’s wrong is to claim that science says so.

Then what about the question whether we are made of math? Well, you can’t falsify this hypothesis. Suppose you had an observation that you can’t describe by math, it could always be that you just haven’t found the right math. So the idea that we’re made of math is also not wrong but unscientific. You can believe it if you want. There’s no evidence for or against it.

I want to finish by saying I am not doing these videos to convince you to share my opinion. I just want to introduce you to some topics that I think are thought-stimulating, and give you a starting point, in the hope it will give you something interesting to think about.

Saturday, July 24, 2021

Can Physics Be Too Speculative?

Imagination and creativity are the heart of science. But look at the headlines in the popular science media and you can’t shake off the feeling that some physicists have gotten ahead of themselves. Multiverses, dark matter, string theory, fifth forces, and that asteroid which was supposedly alien technology. These ideas make headlines, but are then either never heard of again – like hundreds of hypothetical particles that were never detected, and tests of string theory that were impossible in the first place – or later turn out to be wrong – all reports of fifth forces disappeared, and that asteroid was probably a big chunk of nitrogen. Have physicists gone too far in their speculations?

The question how much speculation is healthy differs from the question where to draw the line between science and pseudoscience. That’s because physicists usually justify their speculations as work in progress, so they don’t have to live up to the standard we expect for fully-fledged scientific theories. It’s then not as easy as pointing out that string theory is for all practical purposes untestable, because its supporters will argue that maybe one day they’ll figure out how to test it. The same argument can be made about the hypothetical particles that make up dark matter or those fifth forces. Maybe one day they’ll find a way to test them.

The question we are facing, thus, is similar to the one that the philosopher Imre Lakatos posed: Which research programs make progress, and which have become degenerative? When speculation stimulates progress it benefits science, but when speculation leads to no insights for the description of nature, it eats up time and resources, and gets in the way of progress. Which research program is on which side must be assessed on a case-by-case basis.

Dark matter is an example of a research program that used to be progressive but has become degenerative. In its original form, dark matter was a simple parameterization that fit a lot of observations – a paradigmatic example of a good scientific hypothesis. However, as David Merritt elucidates in his recent book “A philosophical approach to MOND”, dark matter has trouble with more recent observations, and physicists in the area have taken on to accommodating data, rather than making successful predictions.

Moreover, the abundance of specific particle models for dark matter that physicists have put forward are unnecessary to explain any existing observations. These models produce publications but they do not further progress. This isn’t so surprising because guessing a specific particle from rather unspecific observations of its gravitational pull has an infinitesimal chance of working.

Theories for the early universe or fifth forces suffer from a similar problem. They do not explain any existing observations. Instead, they make the existing – very well working – theories more complicated without solving any problem.

String theory is a different case. That’s because string theory is supposed to remove an inconsistency in the foundations of physics: The missing quantization of gravity. If successful, that would be progress in and by itself, even if it doesn’t result in testable predictions. But string theorists have pretty much given up on their original goal and never satisfactorily showed the theory solves the problem to begin with.

Much of what goes as “string theory” today has nothing to do with the original idea of unifying all the forces. Instead, string theorists apply certain limits of their theory in an attempt to describe condensed matter systems. Now, in my opinion, string theorists vastly overstate the success of this method. But the research program is progressing and working towards empirical predictions.

Multiverse research concerns itself with postulating the existence of entities that are unobservable in principle. This isn’t scientific and should have no place in physics. The origin of the problem seems to be that many physicists are Platonists – they believe that their math is real, rather than just a description of reality. But Platonism is a philosophy and shouldn’t be mistaken for science.

What about Avi Loeb’s claim that the interstellar object `Oumuamua was alien technology? Loeb has justified his speculation by pointing towards scientists who ponder multiverses and extra dimensions. He seems to think his argument is similar. But Loeb’s argument isn’t degenerative science. It's just bad science. He jumped to conclusions from incomplete data.
It isn’t hard to guess that many physicists will object to my assessments. That is fine – my intention here is not so much to argue this particular assessment is correct, but that this assessment must be done regularly, in collaboration between physicists and philosophers.

Yes, Imagination and creativity are the heart of science. They are also the heart of science fiction. And we shouldn’t conflate science with fiction.

Saturday, July 17, 2021

What’s the Fifth Force?

[This is a transcript of the video embedded below.]

Physicists may have found a fifth force. Uh, that sounds exciting. And since it sounds so exciting, you see it in headlines frequently, so frequently you probably wonder how many of these fifth forces there are. And what’s a fifth force anyway? Could it really exist? If it exists, is it good for anything? That’s what we’ll talk about today.

Before we can talk about the fifth force, we have to briefly talk about the first four forces. To our best current knowledge, all matter in the universe is made of 25 particles. Physicists collect them in the “standard model” that’s kind of like the periodic table for subatomic particles. These 25 particles are held together by four forces. That’s 1) gravity, apples falling down and all that, 2) the electromagnetic force, that’s a combination of the electric and magnetic force which really belong together, 3) the strong nuclear force that holds together atomic nuclei against the electromagnetic force, and 4) the weak nuclear force that’s responsible for nuclear decay.

All other forces that we know, for example the van-der Waals force that keeps atoms together in molecules, friction forces, muscle forces, these are all emergent forces. That they are emergent means that they derive from those four fundamental forces. And that those forces are fundamental means they are not emergent – they cannot be derived from anything else. Or at least we don’t presently know anything simpler that they could be derived from.

Now, if you say that gravity is a force in the wrong company, someone might point out that Einstein taught us gravity is not a force. Yes, that guy again. According to Einstein, gravity is the effect of a curved space-time. Looks like a force, but isn’t one. Indeed, that’s the reason why physicists, if they want to be very precise, will not speak of four fundamental *forces, but of four fundamental interactions. But in reality, I hear them talk about the gravitational force all the time, so I would say if you want to call gravity a force, please go ahead, we all know what you mean.

As you can tell already from that, what physicists call a force doesn’t have a very precise definition. For example, the three forces besides gravity – the electromagnetic and the strong and weak nuclear force – are similar in that we know they are mediated by exchange particles. So that means if there is a force between two particles, like, say, a positively charged proton and a negatively charged electron, then you can understand that force as the exchange of another particle between them. For the case of electromagnetism, that exchange particle is the photon, the quantum of light. For the strong and weak nuclear force, we also have exchange particles. For the strong nuclear force, those are called “gluons” because they “glue” quarks together, and for the weak nuclear force, these are called the Z and W bosons.

Gravity, again, is the odd one out. We believe it has an exchange particle – that particle is called the “graviton” – but we don’t know whether that particle actually exists, it’s never been measured. And on the other hand, we have an exchange particle to which we don’t associate a force, and that’s the Higgs-boson. The Higgs-boson is the particle that gives masses to the other particles. It does that by interacting with those particles, and it acts pretty much like a force carrier. Indeed, some physicists *do* call the Higgs-exchange a force. But most of them don’t.

The reason is that the exchange particles of electromagnetism, the strong and weak nuclear force, and even gravity, hypothetically, all come out of symmetry requirements. The Higgs-boson doesn’t. That may not be a particularly good reason to not call it a force carrier, but that’s the common terminology. Four fundamental forces, among them is gravity, which isn’t a force, but not the Higgs-exchange, which is a force. Yes, it’s confusing.

So what’s with that fifth force? The fifth force is a hypothetical, new, fundamental force for which we don’t yet have evidence. It we found it, it would be the biggest physics news in 100 years. That’s why it frequently makes headlines. There isn’t one particular fifth force, but there’s a large number of “fifth” forces that physicists have invented and that they’re now looking for.

We know that if a fifth force exists it’s difficult to observe, because otherwise we’d already have noticed it. This means, this force either only becomes noticeable at very long distances – so you’d see it in cosmology or astrophysics – or it become noticeable at very short distances, and it’s hidden somewhere in the realm of particle physics.

For example, the anomaly in the muon g-2, could be a sign for a new force carrier, so it could be a fifth force. Or maybe not. There is also a supposed anomaly in some nuclear transitions, which could be mediated by a new particle, called X17, which would carry a fifth force. Or maybe not. Neither of these anomalies are very compelling evidence, the most likely explanation in both cases is some difficult nuclear physics.

The most plausible case for a fifth force, I think, comes from the observations we usually attribute to dark matter. Astrophysicists introduce dark matter because they do see a force that’s acting on normal matter. The currently most widely accepted hypothesis for this observation is that this force is just gravity, so an old force, if you wish, but that instead there is some new type of matter. That doesn’t fit very well with all observations, so it could be instead that it’s actually not just gravity, but indeed a new force, and that would be a fifth force. Dark energy, too, is sometimes attributed to a fifth force. But this isn’t really necessary to explain observations, at least not at the moment.

If we found evidence for such a new force, could we do anything with it? Almost certainly not, at least not in the foreseeable future. The reason is, if such forces exist, their effects must be very very small otherwise we’d have noticed them earlier. So, you most definitely can’t use it for Yogic flying, or to pin your enemies to the wall. However, who knows, if we do find a new force, maybe one day we’ll figure out something to do with it. It’s definitely worth looking for.

So, if you read headlines about a fifth force, that just means there’s some anomalous observation which can be explained by a new fundamental interaction, most often a new particle. It’s a catchy phrase, but really quite vague and not very informative.

Saturday, July 10, 2021

How Dangerous are Solar Storms?

[This is a transcript of the video embedded below.]

On May twenty-third nineteen sixty-seven, the US Air Force almost started a war. It was during the most intense part of the Cold War. On that day, the American Missile Warning System, designed to detect threats coming from the Soviet Union, suddenly stopped working. Radar stations at all sites in the Northern Hemisphere seemed to be jammed. Officials of the U.S. Air Force thought that the Soviet Union had attacked their radar and began to prepare for war. Then they realized it wasn’t the Soviets. It was a solar storm.

What are solar storms, how dangerous are they, and what can we do about them? That’s what we will talk about today.

First things first, what is a solar storm? The sun is so hot that in it, electrons are not bound to atomic nuclei, but can move around freely. Physicists call this state a “plasma”. If electric charges move around in the plasma, that builds up magnetic fields. And the magnetic fields move more electric charges around, which increases the magnetic fields and so on. That way, the sun can build up enormous magnetic fields, powered by nuclear fusion.

Sometimes these magnetic fields form arcs above the surface of the sun, often in an area of sunspots. These arcs can rip and blast off and then two things can happen: First, a lot of radiation is released suddenly, that’s visible light but also ultraviolet light and up into the X-ray range. This is called a solar flare. The radiation is usually accompanied by some fast moving particles, called solar particles. And second, in some case the flare comes with a shock wave that blasts some of the plasma into space. This is called a “coronal mass ejection,” and it can be billions of tons of hot plasma. The solar flare together with the coronal mass ejection is called a “solar storm”.

A solar storm can last from minutes to hours and can release more energy than the entire power we have spent in human history. The activity of the sun has an 11-year cycle, and the worst solar storms often come in the years after the solar maximum. We’re currently just starting a new cycle and the next maximum of solar activity will be around twenty twenty-five. The statistically most dangerous years of the solar cycle will come after that.

Well, actually. The solar cycle is really 22 years, because after 11 years the magnetic field flips, and the cycle isn’t complete until it flips back. It’s just that for what the solar activity is concerned, 11 years is the relevant cycle.

How do these solar storms affect us? Space is big and most of these solar storms don’t go into our direction. If they do, the solar flare moves at the speed of light and takes about eight minutes to reach us. The radiation exposure that comes with it is a health risk for astronauts and pilots, and it can affect satellites in orbit. For example, during a solar storm in 2003 the Japanese weather satellite Madori 2 was permanently damaged, and many other satellites automatically shut down because their navigation systems were not working. This solar storm became known as the 2003 Halloween storm because it happened in October.

Down here on earth we are mostly shielded from the flare. But not so with the coronal mass ejection. It comes after the flare with a delay of twelve hours to three days, depending on the initial velocity, and it carries its own magnetic field. When it reaches earth, that magnetic field connects with that of Earth. One effect of this is that the aurora becomes stronger, can be seen closer to the equator and can even change color to become red. During the Halloween storm, it could be seen as far south as the Mediterranean and also in Texas and Florida.

The aurora is pretty and mostly harmless, but the magnetic field causes a big problem. Because it changes so rapidly, it induces electric currents. The crust of Earth is not very conductive but our electric grids are, by design, very conductive. This means that the magnetic field from the solar storm moves around a lot of currents in the electric grid, which can damage power plants and transformers, and cause power outages.

How big can solar storms get? The strength of solar storms is measured by the energy output in the solar flare. The smallest ones are called A-class and are near background levels, followed by B, C, M and X-class. This is a logarithmic scale, so each letter represents a 10-fold increase in energy output. There’s no more letters after X, instead one adds numbers after the X, X10, for example is another 10 fold increase after X.

What’s the biggest solar storm on record? It might have been the one from September 2nd, 1859. The solar flare on that day was observed coincidentally by the English astronomer Richard Carrington, which is why it’s known today as the “Carrington event”.

The coronal mass ejection after the flare travelled directly into direction Earth. At the time there weren’t many power grids that could have been damaged because electric lights wouldn’t become common in cities for another two decades or so. But they did have a telegraph system.

A telegrapher in Philadelphia received a severe electric shock when he was testing his equipment, and most of the devices stopped working because they couldn’t cope with the current. But some telegraphers figured out that they could continue using their device if they unplugged it, using just the current induced by the solar storm. The following exchange took place during the Carrington event between Portland and Boston:
    "Please cut off your battery entirely from the line for fifteen minutes."
    "Will do so. It is now disconnected."
    "Mine is disconnected, and we are working with the auroral current. How do you receive my writing?"
    "Better than with our batteries on. – Current comes and goes gradually."
    "My current is very strong at times, and we can work better without the batteries, as the Aurora seems to neutralize and augment our batteries alternately, making current too strong at times for our relay magnets. Suppose we work without batteries while we are affected by this trouble."

How strong was the Carrington event? We don’t know really. At the time two measurement stations in England were keeping track of the magnetic field on earth. But those devices worked by pushing an inked pen around on paper, and during the peak of the storm, that pen just ran off the page. It’s been estimated by Karen Harvey to have had a total energy up to 10³² erg which puts it roughly into the category X45. You can read more about the Carrington event in Stuart Clark’s book “The Sun Kings”.

In twenty thirteen the insurance market Lloyd’s estimated that if a solar storm similar to the Carrington event took place today it would cause damage to the electric grid between zero point six and two point six trillion US dollars – for the United States alone. That’s about twenty times the damage of hurricane Katrina. Power outages could last from a couple of weeks to up to two years because so many transformers would have to be replaced.

The most powerful flare measured with modern methods was the 2003 Halloween Storm. Again it was so powerful that it overloaded the detectors. The sensors cut out at X 17. It was later estimated to have been X 35 +/- five, so somewhat below the Carrington event.

How bad can solar storms get? The magnetic field of our planet shields us from particles that come from the sun constantly, the so-called solar wind. It also prevents those solar particles from ripping the atmosphere off our planet. Mars, for example, once had an atmosphere, but since Mars has a weak magnetic field, its atmosphere was wiped away by solar wind. A solar storm that overwhelms the protection we have from our magnetic field could leave us exposed to the plasma raining down and could in the worst case strip apart some or all of our atmosphere. Can such strong solar storms happen?

Well, I hope you are sitting, because for all I can tell the answer is not obviously “no”. The more energy a solar storm has, the less likely it is. But occasionally astrophysicists observe stars very similar to our Sun that have a solar flare so large they might put life in the habitable zone at risk. They don’t presently know whether such an event is possible for our sun, or how likely it is.

I didn’t know that when I began working on this video. Sorry for the bad news.

What can we do about it? Satellites in orbit can be shielded to some extent. Airplanes can be redirected to lower latitudes or altitudes to limit radiation exposure of pilots and passengers. We can interrupt part of the electric grid to prevent currents from moving around too easily. But besides that, the best we can do is prepare for what’s to come, maybe stock up on toilet paper. How well these preparations work depends crucially on how far ahead we know a solar storm is headed in our direction. That’s why scientists are currently working on solar weather forecasts that might give us a warning already before the flare.

And about those mega-storms. We don’t currently have the technology to do anything about them. So I think the best we can do is to invest in science research and development so that one day we’ll able to protect ourselves.

Thanks for watching, don’t forget to subscribe, see you next week.

Saturday, July 03, 2021

Can we make a new universe?

[This is a transcript of the video embedded below.]

Some people dream of making babies, some dream of making baby universes. Seriously? Yes, seriously. How is that supposed to work? What does it take to make a new universe? And if we make one, what do we do with it? That’s what we’ll talk about today.

At first sight, it seems impossible to make a new universe, because where would you take all that stuff from, if not from the old universe? But it turns out you don’t need a lot of stuff to make a new universe. And we know that from Albert Einstein. Yes, that guy again.

First, Albert Einstein famously taught us that mass is really just a type of energy, E equals m c square and all that. But more importantly, Einstein also taught us that space is dynamic. It can bend and curve, and it can expand. It changes with time. And if space changes with time, then energy is not conserved. I explained this in more detail an earlier video, but here’s a brief summary.

The simplest example of energy non-conservation is the cosmological constant. The cosmological constant is the reason that the expansion of our universe gets faster. It has units of an energy-density – so that’s energy per volume – and as the name says, it’s constant. But if the energy per volume is constant, and the volume increases, then the total energy increases with the volume. This means in an expanding universe, you can get a lot of energy from nothing – if you just manage to expand space rapidly enough. I know that this sounds completely crazy, but this is really how it works in Einstein’s theory of General Relativity. Energy is just not conserved.

So, okay, we don’t need a lot of matter, but how do we make a baby universe that expands? Well, you try to generate conditions similar to those that created our own universe.

There’s a little problem with that, which is that no one really knows how our universe was created in the first place. There are many different theories for it, but none of them has observational support. However, one of those theories has become very popular among astrophysicists, it’s called “eternal inflation” – and while we don’t know it’s right, it could be right.

In eternal inflation, our universe is created from the decay of a false vacuum. To understand what a false vacuum is, let’s first talk about what a true vacuum is. A true vacuum is in a state of minimal energy. You can’t get energy out of it, it’s stable. It just sits there. Because it already has minimal energy, it can’t do anything and you can’t do anything with it.

A false vacuum is one that looks like a true vacuum temporarily, but eventually it decays into a true vacuum because it has energy left to spare, and that extra energy goes into something else. For example, if you throw jelly at a wall, it’ll stick there for a moment, but then fall down. That moment when it sticks to the wall is kind of like a false vacuum state. It’s unstable and it will eventually decay into the true vacuum, which is when the jelly drops to the ground and the extra energy splatters it all over the place.

What does this have to do with the creation of our universe? Well, consider you have a lot of false vacuum. In that false vacuum, there’s a patch that decays into a true vacuum. The true vacuum has a lower energy, but it can have higher pressure. If it has higher pressure, it’ll expand. That’s is how our universe could have started. And in principle you can recreate this situation in the laboratory. You “just” have to create this false vacuum state. Then part of it will decay into a true vacuum. And if the conditions are right, that true vacuum will expand rapidly. While it expands it creates its own space. It does not grow into our universe, it makes a bubble.

This universe creation only works if you have enough energy, or mass, in the original blob of false vacuum. How much do you need? Depends on some parameters of the model which physicists don’t know for sure, but in the most optimistic case it’s about 10 kilograms. That’s what it takes to make a new universe. 10 kilograms.

But how do you create 10 kilograms of false vacuum? No one has any idea. Also, 10 kilograms might not sound much if you’re a rocket scientist, but for particle physicists that’s a terrible lot. The mass equivalent that even the presently biggest particle collider, the large hadron collider, works with is 10 to the minus twenty grams. Now if you collide big atomic nuclei instead of protons, you can bring this up by some orders of magnitude, but 10 kilograms is not something that high energy physicists will work with in my lifetime. No one will create a new universe any time soon.

But, well, in principle, theoretically, we could do it. If you believe this story with the false vacuum and so on. Let us just suppose for a moment that this is correct, what would we do with these universes? Would we potty train them and send them to cosmic kindergarten?

Well, no, because sadly, these little baby-universes don’t stay connected to their mother-universe for long. Their connection is like a wormhole throat, it becomes unstable and pinches off within a fraction of a second. So you’d be giving birth to these universes, kick start their growth, but then, blip, they’re gone. From the outside they would look pretty much like small black holes.

By the way, this could be happening all the time without particle physicists doing anything. Because we don’t really understand the quantum properties of space. So, some people think that space really makes a lot of quantum fluctuations. These fluctuations happen at distances so short we can’t see them, but it could be that sometimes they create one of these baby universes.

If you want to know more about this topic, Zeeya Merali has written a very nice book about baby universes called “A Big Bang in a Little Room”.