Ethan Siegel
banner
startswithabang.bsky.social
Ethan Siegel
@startswithabang.bsky.social
Cosmologist, science communicator, author, speaker, and longtime writer of Starts With A Bang.

Not the next Carl Sagan; the first Ethan Siegel.
How the “meter” came to be exactly one meter long

In the search for a universal standard of distance, scientists have defined and redefined the meter over and over again.

After centuries of change, this 1983 definition should last forever.
bigthink.com/starts-with-...
#physics #measure #meter
How the "meter" came to be exactly one meter long
Until the late 20th century, there wasn't a truly universal standard. Under our current definition, everyone agrees on what "one meter" is.
bigthink.com
November 10, 2025 at 4:55 PM
Starts With A Bang podcast #123 – Alien physics

Do aliens speak the same physics that we do?

@danielwhiteson.bsky.social argues, in his new book and in this fascinating episode, that no, they probably don't.

I disagree; listen to the intense interview here!
bigthink.com/starts-with-...
#aliens
Starts With A Bang podcast #123 - Alien physics
Do aliens speak the same physics that we do, with similar laws, observables, and underlying mathematics. Maybe not, argues Daniel Whiteson.
bigthink.com
November 8, 2025 at 4:42 PM
Can Weber bars detect gravitational waves?

#AskEthan

Starting with 2015's first gravitational wave detection, LIGO/Virgo/KAGRA have now seen hundreds of gravitational waves.

Could the original detector design, Weber bars, work today?

bigthink.com/starts-with-...
#space #astro #physics #weber
Ask Ethan: Can Weber bars detect gravitational waves?
We've now detected hundreds of gravitational waves with LIGO, Virgo, and KAGRA. What if we tried Weber's original method in the modern day?
bigthink.com
November 7, 2025 at 4:52 PM
Our first terraforming goal should be the Moon, not Mars

When we speak about terraforming, Mars is usually the prime target.

But the Moon, due to its proximity, Earth-like soil, and much much more, is a far superior first target.
bigthink.com/starts-with-...
#space #moon #astro #terraforming
Our first terraforming goal should be the Moon, not Mars
The first world beyond Earth for human habitability should be the Moon, not Mars. This is why we should terraform our lunar neighbor first.
bigthink.com
November 6, 2025 at 4:47 PM
How to understand Einstein’s relativity without math

Relativity is so much more than just the math of the Lorentz transformations.

It's a profound new way of looking at the world: one that you can learn to intuit for yourself.
bigthink.com/starts-with-...
#space #astro #physics #relativity
How to understand Einstein's relativity without math
Times dilate and lengths contract near the speed of light. Bizarre and confusing? Sure. But under relativity, it can't be any other way.
bigthink.com
November 5, 2025 at 4:25 PM
Astounding stream of stars caught escaping from nearby galaxy

The Vera Rubin Observatory's "First Look" observations weren't meant for science.

And yet, it revealed a surprising new stellar stream, 160,000 light-years long, escaping from a nearby galaxy.
bigthink.com/starts-with-...
#space #astro
Astounding stream of stars caught escaping from nearby galaxy
Stellar streams are faint trails of stars that appear to "stream" out of galaxies. A new one, escaping galaxy M61, may point to many others.
bigthink.com
November 4, 2025 at 4:51 PM
Fascism has 14 early warning signs, as elucidated by fascism scholar Laurence W. Britt.

In May of this year, the US exhibited "only" 12 of them, as we still lacked a censored press and fraudulent elections.

We're up to 13 on the eve of election day.

Because if you tell the truth, this happens.
November 3, 2025 at 10:44 PM
The Red Spider Nebula gets its JWST glow-up

The US Government may still be shut down, preventing NASA from releasing, well, anything.

Good thing the ESA, a #JWST partner, is still functioning, because now we get to see this.
bigthink.com/starts-with-...
#space #astronomy #astro #science #physics
The Red Spider Nebula gets its JWST glow-up
When dying, Sun-like stars have binary companions, spectacular sights arise from the ionization. JWST spots the Red Spider Nebula in action!
bigthink.com
November 3, 2025 at 5:38 PM
Happy Halloween 2025 everyone, from your old pal Zorak!
October 31, 2025 at 5:16 PM
Could evolving dark energy lead to a Big Crunch?

#AskEthan

It looks like dark energy *may* be evolving in our Universe, as recent DESI data suggests.

But implying that we're headed for a Big Crunch completely oversells what we know.
bigthink.com/starts-with-...
#space #astro #darkenergy
Ask Ethan: Could evolving dark energy lead to a Big Crunch?
There's some, but not overwhelming, evidence that dark energy is evolving. What would it take for a "Big Crunch" to be our cosmic fate?
bigthink.com
October 31, 2025 at 4:17 PM
Reposted by Ethan Siegel
Why the whole isn't greater than the sum of its parts | Ethan Siegel @startswithabang.bsky.social

If the list of things science can’t explain keeps shrinking…should we stop creating gods to fill the gaps?
October 30, 2025 at 4:05 PM
Groupthink in science isn’t a problem; it’s a myth

Scientists get accused of groupthink all the time, and of being unnecessarily resistant to new ideas.

But that's a myth.

The real problem is just how successful our current theories are.
bigthink.com/starts-with-...
#science #space #physics #myth
Groupthink in science isn't a problem; it's a myth
Scientists are notoriously resistant to new ideas. Are they falling prey to groupthink? Or are our current theories just that successful?
bigthink.com
October 30, 2025 at 3:21 PM
Why aliens might not “speak physics” the same way we do

If an alien species achieved interstellar communication or even interstellar travel, can we assume they've developed the same laws of physics as us?

Maybe not, and here's why.
bigthink.com/starts-with-...
#physics #aliens #space #nature
Why aliens might not "speak physics" the same way we do
Physicist Daniel Whiteson challenges the notion that all intelligent species would eventually uncover the same laws of nature. Do you agree?
bigthink.com
October 29, 2025 at 3:21 PM
Neutrinos are still the most mysterious particle we know of

Everyone overlooks the neutrino as an afterthought in our Universe.

But they're the only Standard Model particle with a shot to solve the dark matter, dark energy, and baryogenesis puzzles.
bigthink.com/starts-with-...
#physics #neutrinos
Neutrinos are still the most mysterious particle we know of
Nearly 100 years after being theorized, the strange behavior of the neutrino still mystifies us. They could be even stranger than we know.
bigthink.com
October 28, 2025 at 4:17 PM
Where does the expanding Universe begin?

The Universe doesn't expand everywhere: the space within our atoms, planet, Solar System, galaxy, and Local Group aren't expanding.

So where does that cosmic expansion begin?
bigthink.com/starts-with-...
#space #astronomy #universe #expansion
Where does the expanding Universe begin?
The planet, the Solar System, and the galaxy aren't expanding. But the whole Universe is. So where does the dividing line begin?
bigthink.com
October 27, 2025 at 3:43 PM
Could the Universe have been expanding forever?

#AskEthan

The Universe is expanding today, and looks like it will do so forever.

But was it expanding eternally into the past as well?

Most physicists think "no," and this theorem explains why.
bigthink.com/starts-with-...
#space #physics #astro
Ask Ethan: Why couldn't the Universe have expanded forever?
For 13.8 billion years, the Universe has been expanding. But that couldn't have been the case for an eternity, and science has proven it.
bigthink.com
October 24, 2025 at 3:31 PM
5 undeniable, truthful facts about dark matter

There are always people promoting their own (shoddy) "alternative" ideas to dark matter.

These five undeniable truths box those alternatives into a corner they can't escape from. (Yes, that one too!)
bigthink.com/starts-with-...
#space #astro #physics
5 undeniable, truthful facts about dark matter
Dark matter has never been directly detected, but the astronomical evidence for its existence is overwhelming. Here's what to know.
bigthink.com
October 23, 2025 at 3:42 PM
We still don’t know how “hot” the hot Big Bang was

The earliest stages of the hot Big Bang were far hotter than any conditions that exist in the Universe today.

But things weren't arbitrarily hot; here's what we do (and don't) know today.

bigthink.com/starts-with-...
#space #astro #physics
We still don't know how "hot" the hot Big Bang was
We've long known we can't go back to infinite temperatures and densities. But the hottest part of the hot Big Bang remains a cosmic mystery.
bigthink.com
October 22, 2025 at 4:27 PM
Red dwarfs aren’t uninhabitable; we’re just impatient

No life, as far as we know, could survive on the conditions found on exoplanets around red dwarf stars.

But after many billions of years pass by, perhaps all that will change?
bigthink.com/starts-with-...
#space #astro #life #reddwarf
Red dwarfs aren't uninhabitable; we're just impatient
Red dwarfs are the Universe's most common star type. Their flaring now makes potentially Earth-like worlds uninhabitable, but just you wait.
bigthink.com
October 21, 2025 at 4:00 PM
Is our first “galaxy-quasar hybrid” also a Little Red Dot?

JWST has famously discovered hundreds of "Little Red Dot" objects in the early Universe.

But the first one predates JWST, and was correctly determined to be a galaxy-quasar hybrid
bigthink.com/starts-with-...
#space #astro #jwst #hubble
Is our first "galaxy-quasar hybrid" also a Little Red Dot?
Found by Hubble before JWST's launch, GNz7q looked like a mix of a galaxy and a quasar. Was it actually our first known "Little Red Dot"?
bigthink.com
October 20, 2025 at 4:55 PM
Is the Hubble tension the same thing as dark energy?

#AskEthan

The Hubble tension is a big cosmic puzzle.

Dark energy might be evolving, and still remains mysterious.

But these two problems aren't the same.

Here's what makes them distinct.
bigthink.com/starts-with-...
#space #astro #cosmology
Ask Ethan: Is the Hubble tension the same thing as dark energy?
Observations with the Hubble space telescope helped cement dark energy and reveal the Hubble tension. How are these two things so different?
bigthink.com
October 17, 2025 at 4:30 PM
Reposted by Ethan Siegel
Ethan's piece on Reflect Orbital is today's required reading — he covers ✨every single reason🪩 giant mirrors in space is a bad idea!
The true cost of “solar power at night” with Reflect Orbital

If you played SimCity 2000, you might've loved the idea of "beaming power from space" down to Earth.

Reflect Orbital took that idea, tech-bro'd it, and now could end "night" as we know it.
bigthink.com/starts-with-...
#space #astro
The true cost of "solar power at night" with Reflect Orbital
Solar power has the disadvantage that there's no Sun at night. Satellite startup Reflect Orbital wants to change that, but at what cost?
bigthink.com
October 16, 2025 at 5:47 PM
Reposted by Ethan Siegel
I haven't even read this article yet and I like it!

And I'm not surprised that Ethan is the one to write it.
Yes, reductionism can explain everything in the whole Universe

If we strip reality down to the fundamental particles and their interactions, and add in boundary conditions and initial conditions, can we explain the whole Universe?

Reductionism says yes
bigthink.com/starts-with-...
#space #physics
Yes, reductionism can explain everything in the whole Universe
The whole isn't greater than the sum of its parts; that's a flaw in our thinking. Non-reductionism requires magic, not merely science.
bigthink.com
October 16, 2025 at 4:41 PM
Must there be a single, unified theory of everything?

Daniel Whiteson and Kelly Weinersmith interview me about the topic, and things get a little intense!

Have a listen and see which side of the problem sounds more compelling to you.
www.iheart.com/podcast/105-...
#physics
Must there be a single unified theory of physics? - Daniel and Kelly’s Extraordinary Universe | iHeart
<p>Daniel and Kelly talk to Ethan Siegal about whether we should expect physics to be explained by a single unified theory.</p><p>See <a href='https://omnystudio.com/listener'>omnystudio.com/listener<...
www.iheart.com
October 16, 2025 at 4:39 PM
Yes, reductionism can explain everything in the whole Universe

If we strip reality down to the fundamental particles and their interactions, and add in boundary conditions and initial conditions, can we explain the whole Universe?

Reductionism says yes
bigthink.com/starts-with-...
#space #physics
Yes, reductionism can explain everything in the whole Universe
The whole isn't greater than the sum of its parts; that's a flaw in our thinking. Non-reductionism requires magic, not merely science.
bigthink.com
October 16, 2025 at 4:15 PM