The Inexplicable Cosmic Coincidence That Suggests the Universe Was Designed | Part 1

Was our universe designed to be hospitable to  life? In a recent Astrum video, we saw that there is more dark energy in the universe than  the energy from every single atom and particle of ordinary matter combined. Yet, everything we know  about particles, fields, and quantum mechanics seems to suggest that this apparently large amount  of dark energy could have been—and statistically should have been—much, much larger.

Decades before  astronomers even had any observational evidence for the existence of dark energy, physicists were  shocked to see that the most successful theories of the twentieth century predicted a level of dark  energy so high that stars and galaxies could never have come to exist… let alone life and humanity.  So, how did our universe avoid this fate, and how are we alive today to even ask these questions? I’m Alex McColgan, and you’re watching Astrum.

Join me today as we continue to learn  about the effects of dark energy on the cosmos and explore the maths that claims  we really shouldn’t have existed at all. One of the first things you might learn in a  physics class is that gravity is an attractive force between two objects, whose strength is  proportional to each of their masses. Gravity keeps planets locked in orbit around the Sun, it  keeps stars grouped together in the Milky Way, and it even attracts galaxies together to form  galaxy clusters and superclusters.

But if we zoom out further, this gravitational attraction  begins to act in reverse, causing galaxy clusters to accelerate away from each other rather than  drawing each other in. So, what’s going on here? Einstein’s theory of General Relativity gives us a  lens through which we can understand this strange behavior.

In General Relativity, space isn’t  just some background in which other things can move around; instead, space itself can stretch and  warp and evolve over time. Einstein showed that in this framework, gravity is no longer a force, but  rather a distortion of an object’s inertial path in a dynamical spacetime. For example, when  a planet orbits around the Sun, in Einstein’s description, it’s merely following a straight-line  path in a curved space.

By the same token, what we observe as a repulsive force between galaxy  clusters should really be thought of as an accelerated stretching of the space between them. But what could possibly cause the expansion of space to accelerate like this on the largest  scales of the universe? To begin to answer this question, we need to know what causes spacetime  to stretch and warp to begin with.

In Newton’s theory of gravity, all objects with mass exerted  a gravitational pull, and in General Relativity, all objects with mass curve the spacetime  around them. But Einstein showed that in addition to mass, any form of energy or pressure  will also influence the dynamics of spacetime. Energy density is how much energy is found  within a given volume - how much pop, heat, zap and motion exists within a given space -  and in our universe has always been found to be positive.

Pressure is how much force over an  area the contents of that space sends pushing into the rest of the universe around it – think  interstellar dust pushing on each other whenever they bump into each other in the void. As  you can imagine for objects so far apart, this pressure value hovers a little over 0 on a  cosmic scale. When these values are cumulatively positive, as in the following formula [Show on  screen: Acceleration ∝ -(ρ+3P)] their influence on the space around them causes the space  around them to contract in – essentially, they create gravity by decelerating the  stretching of space.

However, conceivably, if you were somehow to set the values of  this equation so that pressure was negative, and greater than the positive energy density, that  minus sign would cause the whole thing to flip, and you would accelerate the stretching of space.  In effect, you would end up with a volume of space filled with a kind of anti-gravity. A Dark Energy.

It's a little nebulous, as it’s tricky to visualise anything with a truly negative pressure  – how can you have less than 0 atoms in a patch of space, after all? But atoms are not the only  things that exerts pressure. After all, pressure is simply a force applied across an area.

Fields  can also apply forces - think a magnetic field, dragging a piece of iron in towards a bar magnet,  or two magnets pushing each other away. If dark energy were some kind of field that pushed away  not just other magnets, but everything, then this would match what we see the universe doing;  vacuum itself having dark energy, and enough of it to slowly, very gently push the universe apart. Scientists have thought a lot about dark energy over the years, and have even figured out what its  combined energy density and pressure needed to be, to create the rate of spatial expansion that  we witness.

It’s around 10^-9 in SI units, which is a very small number – which is why  we don’t usually notice it here on Earth, and only spot it on the grand cosmological scale  of the universe. This is actually good news, because it turns out that if the number was  much higher or lower than this, things would get very bad for our chance of existing. Let me show you what I mean, with a quick sketch of the history of the universe.

Here  is the full history of the universe, from the moment just after the Big Bang to the present. This is the dark energy density as measured by astronomers. Scientists believe its  negative pressure has kept this density roughly constant for billions of years.

This is the density of ordinary matter in the universe, which has little to no pressure.  The density decreases over time because the expansion of space dilutes the matter within it. Finally, this is the density of radiation in the universe, including photons and other  extremely light particles.

The positive pressure of radiation makes it dilute away  even more quickly than ordinary matter. Towards the beginning of time, for a very short  period, there were no atoms. Very quickly though, protons and neutrons fused together to create the  first atomic nuclei in the very early universe.

Shortly after matter took over as the dominant  form of energy, beating out radiation. The universe cooled down enough for nuclei to attract  and hold onto electrons, forming the first atoms of hydrogen and helium. These atoms were the  building blocks for the very first stars, and these stars were pulled together by  gravity to form the very first galaxies and clusters.

Only later did dark energy take over,  triggering the accelerated expansion of space and preventing the formation of larger structures. But what would have happened if the energy density  were larger? Consider what would have happened if  the pushing force of dark energy were stronger.

It could have been enough to halt the formation of  those early galaxies – pushing apart stars more powerfully than their own gravity could pull  them together. A bit larger than that, and it would have been much more difficult for any stars  to form, either. And if the dark energy density were large enough, we would hardly have had any  atoms or even nuclei produced in the universe.

So, that’s what it could have been. What should  it have been? Using some clever maths and the principles of quantum field theory, scientists  attempted to predict how much the energy density of dark energy ought to have been.

Their result  was… larger than the result we see in nature. How much larger? Their value came in at an astounding  1045 Joules/m3.

Where does the predicted energy density of 10^45 Joules per cubic meter fall  on this graph? It’s (quite literally) off the charts. If that prediction were correct,  the universe today would have no structure, no features, no life—it would be a giant  void filled with nothing but dark energy.

And if the dark energy density were instead a  negative 10^45 Joules per cubic meter, the fate of the universe would be no more promising,  as it would be forced to rapidly collapse in on itself in what’s known as a Big Crunch,  fractions of a second after the universe began. Scientists have attempted to account for their  number being so far off by hypothesising that there exist particles with positive energy  and negative pressure (as yet undiscovered) that even out the maths and bring the answer for  dark energy density back down towards 0. Perhaps there is some massive negative potential  energy source that evens the maths out, a cosmic stretched spring that somehow reigns  in all that rampant energy.

Either that, or quantum field theory is fundamentally wrong.  But as there’s actually quite a lot of evidence supporting quantum field theory, it seems  imprudent to completely throw the idea out. Instead, we are left contemplating the marvellous  nature of this cosmic coincidence.

What were the odds that the energy density of dark energy would  be so low, when it was predicted to be so much higher? That this great universal balancing act  occurred, and in such a way that we weren’t torn apart or crushed into a singularity? Without it  being so low in magnitude, we wouldn’t exist – our very atoms would never have come together, torn  apart by surging, expanding space.

According to our predictions, we have got very lucky. This coincidence happened in just such a way that the universe was able to  produce life. So… Was it a coincidence?

The answer to that question strays from what  we know for sure into what we simply theorise, however. It wanders into the realms of multiverse  theory, and mankind’s quest to understand if we are not here by chance, but by design. There’s  a lot to cover - too much - to cram into the end of this video, and so to do it justice  I’ve split this one in two.

I’ll cover the rest when I have the time to do it full justice. In the meantime, what do you think? Our existence so far appears to be excessively fortunate.

How  do you think it happened? Leave your answer in the comments below, and see if other people’s ideas  match or contrast with your own. It’s always good to hear other viewpoints, particularly for  a subject where there aren’t clear-cut answers.

You never know what you might find out. Our existence is surprising. Perhaps that means the Universe has more surprises in store  for us, if we can only find the answers.