*[This is a transcript of the video embedded below. Some of the explanations may not make sense without the animations in the video.]*

Did the universe come out of a black gap? Will the large bang repeat? Was the universe created from strings? Physicists have numerous concepts about how the universe started, and I’m continuously requested to touch upon them. On this video I wish to clarify why you shouldn’t take these concepts significantly. Why not? That’s what we’ll discuss in the present day.

The primary proof that the universe expands was found by Edwin Hubble who noticed that close by galaxies all transfer away from us. How this might occur was defined by none apart from Albert Einstein. Sure, that man once more. His idea of normal relativity says that house responds to the matter and power in it by increasing.

And so, as time passes, matter and power within the universe change into extra thinly diluted on common. I say “on common” as a result of inside galaxies, matter doesn’t dilute however really clumps and house doesn’t broaden. However on this video we’ll solely have a look at the typical over the whole universe.

So we all know that the universe expands and on common matter in it dilutes. But when the universe expands in the present day, this implies if we glance again in time the matter should have been squeezed collectively, so the density was larger. And a better density of matter means a better temperature. This tells us that within the early universe, matter was dense and scorching. Actually scorching. In some unspecified time in the future, matter should have been so scorching that atoms couldn’t hold electrons round them. And even earlier, there wouldn’t even have been particular person atomic nuclei, only a plasma of elementary particles like quarks and gluons and photons and so forth. It’s just like the alphabet soup of physics.

And earlier than that? We don’t know. We don’t know as a result of we now have by no means examined what matter does at power densities larger than these which the Giant Hadron Collider can produce.

Nevertheless, we are able to simply ignore this problem, and proceed utilizing Einstein’s equations additional again in time, assuming that nothing adjustments. What we discover then is that the power density of matter should as soon as have been infinitely giant. This can be a singularity and it’s the place our extrapolation into the previous breaks down. The second at which this occurs is roughly 13 level seven billion years previously and it’s referred to as the Massive Bang.

The Massive Bang didn’t occur at any explicit place in house, it occurred in all places. I defined this in additional element on this earlier video.

Now, most physicists, me included, suppose that the Massive Bang singularity is a mathematical artifact and never what actually occurred. It most likely simply implies that Einstein’s idea stops working and we ought to be utilizing a greater one. We predict that’s what’s occurring, as a result of when singularities happen in different circumstances in physics, that’s the explanation. For instance, when a drop of water pinches off a faucet, then the floor curvature of the water has a singular level. However this occurs provided that we describe the water as a clean fluid. If we might take note of that it’s really manufactured from atoms, then the singularity would go away.

One thing like that’s most likely additionally why we get the Massive Bang singularity. We ought to be utilizing a greater idea, one that features the quantum properties of house. Sadly, we don’t have the speculation for this calculation. And so, all that we are able to reliably say is: If we extrapolate Einstein’s equations again in time, we get the Massive Bang singularity. We predict that this isn’t bodily right. So we don’t know the way the universe started. And that’s it.

Then how come that you just continuously examine all these different concepts for a way the universe started? Since you have been sitting round at your dentist and had nothing else to do. Okay, however why do physicists put ahead such concepts when the reply is we simply don’t know. Like, you might have lately seen some movies about how our universe was allegedly born from a black gap.

The difficulty is that physicists can’t settle for the scientifically sincere reply: We don’t know, and depart it at that. As an alternative, they alter the extrapolation again in time through the use of a distinct set of equations. After which you are able to do all sort of different issues, actually just about something you need.

However wait, that is science, proper? You don’t simply get to make up equations. Until potential you’re adorning a black board for a TV crew. Although, really, I did this as soon as and later they requested me what these equations have been and I needed to inform them they don’t imply something which was actually embarrassing. So even on this case my recommendation can be, you shouldn’t make up equations. However in cosmology they do it anyway. Right here’s why.

Suppose you’re throwing a stone and also you calculate the place it falls utilizing Newton’s legal guidelines. If I provide the preliminary place and velocity, you’ll be able to calculate the place the stone lands. We name the preliminary place and velocity the “preliminary state”, and the equation by which you calculate what occurs the “evolution regulation”.

You may as well use this equation the opposite method spherical: if you realize the ultimate state, that’s, the place and velocity in the mean time the stone landed, you’ll be able to calculate the place it’s been at any time in between, and the place it got here from. It’s sort of like when my children have chocolate throughout their fingers, I can deduce the place that got here from.

Okay, however you didn’t come right here to listen to me discuss stones, this video was supposedly in regards to the universe. Nicely, in physics all theories we presently have work this fashion, even that for the whole universe. The equations are extra sophisticated, alright, however we nonetheless have an preliminary state and an evolution regulation. We put in some preliminary state, calculate how it will appear like in the present day, and evaluate that with our observations to see if it’s right.

However wait. On this case we are able to solely inform that the preliminary state and the equations *collectively give the right prediction for the ultimate state. How can we inform that the equations alone are right?

Let’s have a look at the stone instance once more. You may throw many stones from totally different locations with totally different preliminary velocities and verify that they all the time land the place the equations say. You may additionally, say, take a video of the flight of the stone and verify that the place at any second agrees with the equations. I do not suppose that video would kill it on TikTok, however you by no means know, individuals watch the weirdest shit.

However in cosmology we are able to’t try this. We have now just one universe, so we are able to’t take a look at the equations by altering the preliminary situations. And we are able to’t take any snapshots in between as a result of we’d have to attend 13 billion years. In cosmology we solely have observations of the ultimate state, that’s, the place the stone lands.

That’s an issue. As a result of then you’ll be able to take no matter equation you need and use it to calculate what occurred earlier. And for every potential equation there will probably be *some earlier state that, when you use the equation within the different path, will agree with the ultimate place and velocity that you just noticed. So it looks as if in cosmology we are able to solely take a look at a mix of preliminary state and equation however not discover out what both is individually. After which we are able to’t say something about how the universe started.

That sounds unhealthy. However the state of affairs isn’t fairly as unhealthy for 2 causes.

First: the equations we use for the whole universe have been confirmed by *different observations wherein we *can use the usual scientific strategies. There are numerous experiments which present that Einstein’s equations of Basic Relativity are right, for instance redshift within the gravitational discipline, or the perihelion precession of Mercury, and so forth. We then take these well-confirmed equations and apply them to the whole universe.

This, nevertheless, doesn’t totally resolve the issue. That’s as a result of in cosmology we use additional assumptions in addition to Einstein’s equations. For instance, we use the cosmological precept about which I talked in an earlier video, or we assume that the universe accommodates darkish matter and darkish power and so forth. So, saying that we belief the equations as a result of they work in different circumstances doesn’t justify the present cosmological mannequin.

However we now have a second motive which *does justify it. It’s that Einstein’s equations along with their preliminary values within the early universe present a easy *rationalization for the observations we make in the present day. Once I say easy I imply easy in a quantitative method: you want few numbers to specify it. For those who used a distinct equation, then the preliminary state can be tougher. You’d must put in additional numbers. And the speculation wouldn’t clarify as a lot.

Simply consider the equations as a sort of machine. You set in some assumptions about how the universe started, do the maths, and also you get out a prediction for the way it appears like in the present day. This can be a good rationalization if the prediction agrees with observations *and the preliminary state was easy. The easier the higher. And for this you solely want the observations from in the present day, you don’t want to attend some billion years. Until after all you wish to. You already know what? Let’s simply wait collectively.

Okay. How about you wait, and we discuss once more in 10 billion years.

When you wait, the cosmologists who aren’t affected person sufficient justify utilizing one explicit equation and one explicit preliminary state by exhibiting that this *mixture is an easy rationalization within the sense that we are able to calculate numerous knowledge from it. The best rationalization that we now have discovered is the usual mannequin for cosmology, which can also be referred to as LamdaCMD, and it’s based mostly on Einstein’s equations.

This mannequin explains for instance how our observations of the cosmic microwave background matches along with our observations of galactic filaments. They got here out of the identical preliminary distribution of matter, the alphabet soup of the early universe. If we used a distinct equation, there’d nonetheless be some preliminary state, nevertheless it wouldn’t be easy any extra.

The requirement that a proof is straightforward is tremendous vital. And it’s not simply because in any other case individuals go to sleep earlier than your achieved explaining. It’s as a result of with out it we are able to’t do science in any respect. Take the concept the Earth was created 6000 years in the past with all dinosaur bones in place as a result of god made it so. This isn’t unsuitable. Nevertheless it isn’t easy, so it’s not a scientific rationalization. Evolution and geology in distinction are easy explanations for a way these dinosaur bones ended up the place they’re. I defined this in additional element in my new e-book Existential Physics which has simply appeared.

That stated, allow us to then have a look at what physicists do once they discuss totally different concepts for a way the universe started. For this, they alter the equations as we return in time. Sometimes, the equations are similar to Einstein’s equations at the moment, however they differ early within the universe. After which in addition they want a distinct preliminary state, so that you would possibly now not discover a Massive Bang. As I stated earlier, you’ll be able to all the time do that, as a result of for any evolution regulation there will probably be some preliminary state that offers you the fitting prediction for in the present day.

The issue is that this makes a easy rationalization extra sophisticated, so these theories are usually not scientifically justifiable. They don’t enhance the explanatory energy of the usual cosmological mannequin. One other strategy to put it’s that every one these sophisticated concepts for a way the universe started are pointless to elucidate what we observe.

It’s really worse. Since you would possibly suppose we simply have to attend for higher observations after which possibly we’ll see that the present cosmological mannequin is now not the only rationalization. But when there was an earlier section of the universe that was certainly extra sophisticated than the easy preliminary state that we use in the present day, we couldn’t use the scientific technique to resolve whether or not it’s right or not. The scientific technique as we all know it simply doesn’t cowl this case. Science fails!

Certain, making higher observations will help us enhance the present fashions a little bit extra. However ultimately we’ll run into this drawback that extra sophisticated explanations are all the time potential, and by no means scientifically justified.

So what’s with all these concepts in regards to the early universe. Right here’s one which’s been sort of fashionable lately, an concept that was put ahead by Nikodem Poplawski. For this, you alter normal relativity by including new phrases to the equations referred to as torsion. This removes the large bang singularity, and replaces it with a bounce. Our universe then got here out of a bottleneck that’s fairly much like a black gap, simply with out the singularity. Are you able to do that? You’ll be able to actually do that within the sense that there’s maths for it. However on that depend you are able to do many different issues. Like broccoli. There’s maths for broccoli. So why not make the universe out of broccoli?

I do know this sounds loopy, however there are numerous examples for this, like Penrose’s cyclic cosmology that we talked about some months in the past. Or the ekpyrotic universe which begins with a collision of upper dimensional membranes. Or the concept we got here out of a 5-dimensional black gap which made headlines just a few years in the past. Or the concept the universe started with a gasoline of strings which appears to by no means have been notably fashionable. Or the no-boundary proposal which has it that the universe started with solely house and no time, an concept put ahead by Jim Hartle and Stephen Hawking. Or geometrogenesis, which is the concept the universe started as a extremely related community that then misplaced most of its connections and condensed into one thing that’s indistinguishable from the house we inhabit. And so forth.

The physicists who work on this all the time give you some predictions for observables. However since these hypotheses are already unnecessarily sophisticated anyway, you can also make them match to any potential commentary. And even when you’d rule out a few of them, there are infinitely many others you could possibly make up.

This doesn’t imply that these concepts are unsuitable. It simply implies that we are able to’t inform in the event that they’re proper or unsuitable. My buddy Tim Palmer instructed to name them ascientific. Relating to the query how the universe started, we face the bounds of science itself. It’s a query I believe we’ll by no means have the ability to reply. Identical to we’ll by no means have the ability to reply the query of why girls pluck off their eyebrows after which paint them again on. Some questions defy solutions.

So when you learn yet one more headline about some physicist who thinks our universe may have begun this fashion or that method, you must actually learn this as a creation fable written within the language of arithmetic. It’s not unsuitable, nevertheless it isn’t scientific both. The Massive Bang is the only rationalization we all know, and that’s most likely unsuitable, and that’s it. That’s all that science can inform us.