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Since the dawn of humanity around 100 billion people have lived. How many will live in the future of our species? We might hope for a trillion times that if we colonize the galaxy. But a simple statistical argument tells us that the doom of our species is much, much closer.

Hosted by Matt O’Dowd
Written by Matt O’Dowd
Graphics by Leonardo Scholzer & Adriano Leal
Directed by: Andrew Kornhaber
Executive Producers: Eric Brown & Andrew Kornhaber

End Credits Music by J.R.S. Schattenberg: https://www.youtube.com/channel/UCRl6-nb4iOnsij-vnpAjp0Q

In some recent episodes we’ve explored the anthropic principle and seen how it can be used to explain the fact that both our planet and our universe seem very finely tuned to allow the development of life. Our planet and/or universe can be rare and unlikely as long as there are enough other planets and/or universes to stack the odds in favour of our existence. We touched on both the potential power and potential misuse of this principle. Today we’re going to push our luck, and see how this controversial idea can be used to predict the physics of our universe, and also to predict the imminent demise of the human race.

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The universe is big, really, really big. Although according to a new paper, it may literally be infinitely smaller than we previously thought.

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Hosted by Matt O’Dowd
Written by Matt O’Dowd
Graphics by Leonardo Scholzer & Adriano Leal
Directed by: Andrew Kornhaber
Executive Producers: Eric Brown & Andrew Kornhaber

End Credits Music by J.R.S. Schattenberg: https://www.youtube.com/channel/UCRl6-nb4iOnsij-vnpAjp0Q

Every time you walk out the door, light from the Big Bang strikes your face, enters your eyes. This is the cosmic microwave background radiation – the left-over heat-glow from the very early universe. We can’t see this microwave light with our eyes, but we can catch it with even a simple radio antenna. As soon as we became aware of its existence we’ve been feverishly building better and better devices to collect it. Why? Because it encodes so many secrets. And within this light, a group of scientists have just found evidence of the limits of space. A clue that our universe may be actually be finite in size. Today on Space Time Journal Club we’ll delve into the Nature Astronomy paper that just reported this: Planck evidence for a closed Universe and a possible crisis for cosmology by Eleonora Di Valentino, Alessandro Melchiorri, and Joe Silk.

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The moment you started observing reality, you hopelessly polluted any conclusions you might make about it. The anthropic principle guarantees that you are NOT seeing the universe in most typical state. But used correctly, this highly controversial idea can be extremely powerful. So, how do you correctly use the anthropic principle?

Hosted by Matt O’Dowd
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Special Thanks to Dr. Flournoy!!! Check out his lectures Below:
Particle Physics: https://www.youtube.com/playlist?list=PLDlWMHnDwylijo0yfs3xUN9ad6-YZjPLT
General Relativity: https://www.youtube.com/playlist?list=PLDlWMHnDwyliMevB36wgRbjXhJkoN_RUQ

According to the original definitions by Brandon Carter, the weak anthropic principle states that we must live in a place and time in the universe capable of supporting observers – in our case, a habitable biosphere, and the strong anthropic principle, which states that the universe itself must have the conditions necessary for producing environments that, in turn, produce observers. That means the fundamental constants and initial conditions of the universe must be just right to allow nice habitable planets to one day form. Let’s just call it the anthropic principle: we necessarily observe from an environment capable of producing observers; be that environment a planet within a universe or a universe within a multiverse.

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Life exists in our universe. There we go – one hopefully uncontroversial statement. Therefore our universe is capable of producing and supporting life. How am I going? Two for two? Let’s try for three: therefore there are countless universes. Hmmm. Did I break my streak?

Hosted by Matt O’Dowd
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Our universe seems to operate according to a set of fundamental rules that we try to understand and model with the equations of our laws of physics. Those equations always include one or more fundamental constants – simple numbers that set the scale for the equation. We can’t determine the values of these constants from pure theory – we have to measure them in the real universe. These are things like the speed of light, the Planck constant, the masses of the elementary particles, and the constants defining the relative strengths of the fundamental forces – the so-called coupling constants.

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Why does it appear, that humanity is the lone intelligence in the universe? The answer might be that planet Earth is more unique than we’ve previously assumed. The rare earth hypothesis posits exactly this – that a range of factors made Earth exceptionally unusual and uniquely able to produce intelligent life.

In upcoming episodes we’ll be exploring the anthropic principle and its two main versions – the strong and the weak anthropic principles. The strong anthropic principle tells us that the observed universe must be able to produce observers – including the contentious idea that this predicts the existence of universes beyond our own. But in today’s episode we’re going to focus on the weak anthropic principle. It says that we must find ourselves in a part of the universe capable of supporting us. For example, in a planetary biosphere rather than floating in the void between the galaxies. This may seems tautological, but accounting for this observer selection bias is important to understanding why the universe looks the way it does from our perspective. And the weak anthropic principle is much more useful than that. When combined with the apparent absence of alien civilizations, it may tell us why intelligent life is incredibly rare in our universe.

Hosted by Matt O’Dowd
Written by Matt O’Dowd
Graphics by Leonardo Scholzer & Adriano Leal
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Invitation to Time Travelers: https://www.youtube.com/post/UgzeIA0O00-bVioxU4t4AaABCQ

Time travel stories are cool because both the past and future are somehow more interesting that the present and because everyone wants a redo. But so far it appears we’re doomed to live consumed by regret in the eternal, boring present. Time marches on, inexorably and only forward. Or so we thought until Einstein came along. His special and general theories of relativity changed the way we think about time forever, and believe it or not, their raw equations permit time travel. They even tell us how to do it. So let’s review the possibilities, and decide how possible they really are.

Hosted by Matt O’Dowd
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Directed by: Andrew Kornhaber
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It’s time we talked about loop quantum gravity. What exactly is it? What are the loops? And can it really defeat string theory in our quest for a Theory of Everything?

Hosted by Matt O’Dowd
Written by Graeme Gossel & Matt O’Dowd
Graphics by Leonardo Scholzer
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End Credits Music by J.R.S. Schattenberg: https://www.youtube.com/channel/UCRl6-nb4iOnsij-vnpAjp0Q

The holy grail of physics is to connect our understanding of the tiny scales of atoms and subatomic particles with that of the vast scales of planets, galaxies, and the entire universe. To connect quantum physics with Einstein’s general theory of relativity. Our search for a theory of quantum gravity is a century old, and we’ve talked quite a bit about it already, including what’s probably the lead contender – string theory. But string theory isn’t the only game in town – or so some physicists believe. There may be another way to reconcile the physics of the tiny and the gigantic – another way to a theory of quantum gravity that avoids a lot of conceptual baggage like tiny wiggling strings made of coiled up extra dimensions. That other way would be loop quantum gravity, and today we’re going to learn exactly what it is.

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Black holes are crazy enough on their own – but crash two together and you end up with a roiling blob of inescapable space that vibrates like a beaten drum. And the rich harmonics of those vibrations, seen through gravitational waves, could hold the secrets to the nature of the fabric of spacetime itself. Today on space time journal club we’ll explore the papers that claim to have detected black hole harmonics. We’ll also give you the latest updates on the most recent – in some cases quite bizarre – LIGO detections.

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Hosted by Matt O’Dowd
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Graphics by Murilo Lopes
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End Credits Music by J.R.S. Schattenberg: https://www.youtube.com/channel/UCRl6-nb4iOnsij-vnpAjp0Q

When physicists talk about black holes they’re usually referring to highly theoretical objects – static, unchanging black holes viewed from “infinitely” far away. This makes everything clean and simple enough to attempt the already notoriously complex calculations of black hole physics. But real black holes are created in the violent deaths of massive stars, and there’s nothing clean about that. And we now know that black holes merge – and in the process produce gravitational radiation that we’ve only just managed to detect with the miraculous work of the LIGO and VIRGO gravitational wave observatories. In the instant after its merger, the new, joined black hole looks nothing like the idealized theoretical black hole.

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The universe is big, but it’s peanuts compared to the eternally inflating multiverse. But just how many universes are there? What are they like? And most importantly, what can they tell us about … aliens?

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End Credits Music by J.R.S. Schattenberg: https://www.youtube.com/channel/UCRl6-nb4iOnsij-vnpAjp0Q

Imagine it: the observable part of our universe is 93 billion light years across, and that’s just a small fraction of the stuff created in our Big Bang. But in the eternal inflation picture, ours is just one among uncountable bubble universes. Bubbles that are continuously appearing and growing within a vastly larger spacetime that itself expands at an exponentially accelerating rate. A greater inflationary spacetime whose expansion never ends. We looked at the bizarre idea of eternal inflation in recent episodes – but we stopped short of exploring the full implications of this proposition. Those implications are, frankly, completely nuts. Some may also be true.

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You know what a planet is, right? A big round thing that orbits a star. Uh, not so fast. The surprisingly vicious debate over the planetary status of Pluto has given us a fascinating glimpse into what a scientific definition really is. And perhaps the word planet is too vague to be used as a scientific definition at all.

Hosted by Matt O’Dowd
Written by Drew Rosen and Matt O’Dowd
Graphics by Leonardo Scholzer
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We love to classify things. Labels help us keep stuff organized in our heads. In science, categorization provides a fast and easy way to know the properties of a member of the group just by knowing what group it belongs to. Chemists group elements on the periodic table, those groups exhibit similar chemical behavior that reflect outer-shell electron number. Biologists group organisms by similar physical characteristics, and this taxonomy reflects genetic relationships. Astronomers are all about space taxonomy. We classify galaxies based on their shape, black holes based on how they feed, stars based on their colour and brightness, and planets by… well, by a set of criteria that has caused more tension and heartbreak than any made-up grouping scheme really should. Because a change in that scheme demoted Pluto from planet to not-planet. Today we’re going to settle whether this was reasonable, and whether we should keep the word “planet” at all.

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