Ethan Siegel

How many times must you fold a paper to reach the Moon?

A single sheet of paper is incredibly thin: about 0.1 millimeters (0.004 inches) thick.

But fold it, and it doubles in thickness. Fold it again, and it doubles again.

How many folds to the Moon?

How many times must you fold a paper to reach the Moon? Each time you fold a piece of paper, you double the paper's thickness. It doesn't take all that long to even reach the Moon.

Starts With A Bang podcast #101 – Quantum Computing

We have a new podcast out, on the topic of quantum computing.

The science is fascinating, but so much of what you've heard surrounding it is hype, not reality.

Get the real info today!

Starts With A Bang podcast #101 - Quantum Computing Here in the 21st century, quantum computing is quickly going from a dream to a reality. But what's hype, and what's actually true?

What if the Sun were a grain of sand?



To shrink the Sun down to the size of a grain of sand is a reduction in scale of around 2.8 trillion.

At those new sizes, what would the Universe look like?

Ask Ethan: What if the Sun were a grain of sand? The cosmic scales governing the Universe are almost unbelievably large. What if we shrunk the Sun down to be just a grain of sand?

How much energy does the Sun produce?

It took a lot of steps to figure out the answer, and we've known "how much" for less than 200 years.

Here's how we got there, and how you could figure it out for yourself.

How much energy does the Sun produce? Figuring out the answer involved a prism, a pail of water, and a 50 year effort by the most famous father-son astronomer duo ever.

How humanity’s most enduring calendar failed us all

The Julian calendar endured for nearly 1600 years, and was finally replaced for good reason.

But not everywhere, and not at once, and its replacement isn't perfect either.

How humanity's most enduring calendar failed us all With the invention of the leap year, the Julian calendar was used worldwide for over 1500 years. Over time, it led only to catastrophe.

What was it like when the Universe formed the most stars?

More than 10 billion years ago, the Universe's star-formation rate peaked.

Today, it's just ~3% of what it was back in its heyday.

What was it like when the Universe formed the most stars? Today, the star-formation rate across the Universe is a mere trickle: just 3% of what it was at its peak. Here's what it was like back then.

What was it like when life first became possible?

Earth wasn't created until more than 9 billion years after the Big Bang.

In some lucky places, life could have arisen almost right away: perhaps more than 8 billion years before the formation of Earth.

What was it like when life first became possible? Earth wasn't created until more than 9 billion years after the Big Bang. In some lucky places, life could have arisen almost right away.

What was it like when the first galaxies began to form?

Even once the first stars had already formed, it still took a while for the Universe to make its first galaxies.

Here's what that epic transition time was like.

What was it like when the first galaxies began to form? Even after the first stars form, those overdense regions gravitationally attract matter and also merge. Here's how they grow into galaxies.

What was it like when the first “polluted” stars formed?

The first generation of stars were pristine.

All generations thereafter were "polluted" by the ashes of the first stars.

Here's why that makes such a cosmic difference.

What was it like when the first "polluted" stars formed? The first stars in the Universe were made of pristine material: hydrogen and helium alone. Once they die, nothing escapes their pollution.

What was it like when the first stars began to shine?

It took minutes to make elements, a few hundred thousand years to make atoms, but tens or even hundreds of millions of years to make stars.

Here's why the first ones were so special.

What was it like when the first stars began to shine? The Big Bang's hot glow faded away after only a few million years, leaving the Universe dark until the first stars formed. Oh, the changes!

The top 15 JWST images of 2023

It's been an incredible year for astrophysics discoveries, with JWST leading the way.

Here are 15 of its most important images... and the discoveries that came with them.

The top 15 JWST images of 2023 The Universe is an amazing place. Under the incredible, infrared gaze of JWST, it's coming into focus better than ever before.

JWST’s new and improved exam of Uranus shines

In February of 2023, JWST viewed Uranus for the first time.

In September, it viewed Uranus again: in more filters (4 vs. 2) and a little closer to solstice.

Here's what's brand new.

JWST's new and improved exam of Uranus shines As Uranus approaches its solstice, its polar caps, rings, and moons come into their best focus ever under JWST's watchful eye. See it now!

The 10 biggest physics and astronomy lies from 2023

Plenty of untrue stories in physics in astronomy got reported as though they were real.

Here's what's actually true, versus what you might've read.

The 10 biggest physics and astronomy lies from 2023 Misinformation was extremely popular in 2023, as bad science often made global headlines. Make sure you the truth behind these 10 stories.

Do any particles not have antiparticles?



Not every particle is either matter or antimatter, and not every particle has a separate antiparticle.

But at least everyone has something that can annihilate them completely away!

Ask Ethan: Do any particles not have antiparticles? In our Universe, matter is made of particles, while antimatter is made of antiparticles. But sometimes, the physical lines get real blurry.

What was it like when no stars yet existed?

It took less than half a million years to make neutral atoms, but 50-100 million years before even the very first stars formed.

Here's what it was like in those in-between times.

What was it like when no stars yet existed? Atomic nuclei form in minutes, atoms form in hundreds of thousands of years, but the "dark ages" rule thereafter, until stars finally form.

The scientific hazards of being Santa Claus

Santa Claus might seem like he has the best job in the world.

But when it comes to workplace health and safety issues, there's a lot more protection that's sorely needed.

The scientific hazards of being Santa Claus With any occupation comes a risk of health and safety hazards. When it comes to being Santa Claus, the challenges are unique.

The act of ice skating is a miracle of physics

There's some incredible physics involved with ice skating, including this fact: below a certain temperature, it's actually too cold to ice skate!

The act of ice skating is a miracle of physics While ice itself is slick, slippery, and difficult to navigate across under most circumstances, skaters easily glide across the ice.

10 fun facts as Halley’s Comet makes its big comeback

After reaching aphelion on December 9, 2023, Halley's comet now heads back towards the inner Solar System for its 2061 appearance.

How many of these fun facts did you know?

10 fun facts as Halley's Comet makes its big comeback On December 9, 2023, Halley's Comet reached aphelion: its farthest point from the Sun. As it returns, here are 10 facts you should know.

Starts With A Bang podcast #100 – Galaxies in the JWST era

It's my 100th podcast!

Featuring Dr. Jeyhan Kartaltepe of the CEERS collaboration, who's been observing the early Universe with JWST.

What we found is amazing, and no, "cosmology isn't broken."

Starts With A Bang podcast #100 - Galaxies in the JWST era Since JWST first glimpsed the Universe, we've entered a new era in understanding the earliest objects in the Universe. What have we learned?

Is it possible that gravity isn’t quantum?



Is there even a quantum theory of gravity for nature to obey?

Here's why we should give the new "postquantum theory of classical gravity" a fighting chance.

Ask Ethan: Is it possible that gravity isn't quantum? For generations, physicists have been searching for a quantum theory of gravity. But what if gravity isn't actually quantum at all?

What was it like when the first atoms formed?

It took just minutes to make the first atomic nuclei, but hundreds of thousands of years to make atoms.

Here's the incredible story of how the Universe does it, complete with an incredible quantum twist.

What was it like when the first atoms formed? The first elements in the Universe formed just minutes after the Big Bang, but it took hundreds of thousands of years before atoms formed.

Will 2023’s Geminids be the best of all-time?

The Geminids are coming.

Every three years, they're better than ever, and 2023's is not only on that "third" year, but there's a new Moon to help you out.

Will this year's be the best show ever?

Will 2023's Geminids be the best of all-time? Each December, the Geminid meteor shower puts on a show for skywatchers across Earth. With a new Moon at 2023's peak, it'll be outstanding!

“Singularities don’t exist,” claims black hole pioneer Roy Kerr

In 1963, Roy Kerr discovered the spacetime solution for a rotating black hole: with mass and spin.

60 years later, he's demolished the so-called proof that they have singularities inside them.

"Singularities don't exist," claims black hole pioneer Roy Kerr The brilliant mind who discovered the spacetime solution for rotating black holes claims singularities don't physically exist. Is he right?

Pulsars murder their companion stars, X-rays reveal

If you're a star in a tight orbit around a pulsar, I've got bad news.

That pulsar's going to steal your material, spin up, and then use your stolen material to kill you.

For real.

Pulsars murder their companion stars, X-rays reveal Nearly half of all stars are born in binary systems, with the most massive ones dying the fastest. It's not pretty for the "second" star.

Why is there no antigravity?



In our Universe, gravity is always attractive, never repulsive.

But things didn't have to be that way, and under the right conditions, they might not always be.

Ask Ethan: Why is there no antigravity? In General Relativity, the matter and energy curve spacetime, which we experience as gravity. Why can't there be an "antigravity" force?

What was it like when the first elements formed?

Most of the heavy elements, today, were made in stars.

But the light ones weren't.

Instead, they were made in the early Universe... but not as early as you might think!

What was it like when the first elements formed? Early on during the hot Big Bang, there were only free protons and neutrons: no atomic nuclei. How did the first elements form from them?

What was it like when the last antimatter disappeared?

Today, our Universe is practically all composed of matter, with only a slight amount of antimatter produced by high-energy processes.

But for the first three seconds, antimatter was everywhere.

What was it like when the last antimatter disappeared? In the early stages of the hot Big Bang, matter and antimatter were (almost) balanced. After a brief while, matter won out. Here's how.

The simplest explanation for ultra-high-energy cosmic rays

A cosmic ray particle struck Earth in 2021 with extreme energy: about 5 times as great as should be allowed.

There's no deep, puzzling mystery.

But there is an extremely simple explanation.

The simplest explanation for ultra-high-energy cosmic rays The highest-energy particles could be a sign of new, unexpected physics. But the simplest, most mundane explanation is particularly iron-ic.

JWST now owns the top 8 spots for most distant objects

In 2022, the most distant object ever known was GN-z11, found by Hubble in 2015/6.

Today, that's only the 9th most distant object, with all top 8 spots being objects discovered by JWST.

JWST now owns the top 8 spots for most distant objects In 2022, Hubble owned the record for most distant galaxy. Today, that galaxy is down to the 9th most distant object. Thanks, JWST.