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   John Carlos Baez (johncarlosbaez@mathstodon.xyz)'s status on Sunday, 28-Jan-2024 04:54:19 JST John Carlos Baez

   If our civilization collapses, extraterrestrial archeologists can look at this and be impressed. Three satellites following the Earth in an equilateral triangle, each 25 million kilometers from the other two. Each contains two gold cubes in free-fall. The satellites accelerate just enough so they don't get blown off course by the solar wind. The gold cubes inside feel nothing but gravity.

   Lasers bounce between each cube and its partner in another satellite, measuring the distance between them to an accuracy of 20 picometers: less than the diameter of a helium atom! This lets the satellites detect gravitational waves — ripples in the curvature of spacetime — with very long wavelengths, and correspondingly low frequencies.

   It should see so many binary white dwarfs, neutron stars and black holes in the Milky Way that these will be nothing but foreground noise. More excitingly, it should see mergers of supermassive black holes at the centers of galaxies as far as... the dawn of time, or whenever such black holes were first formed. (The farther you look, the older things you see.)

   It may even be able to see the "gravitational background radiation", the thrumming vibrations in the fabric of spacetime left over from the Big Bang. This radiation was created before the hot gas in the Universe cooled down enough to become transparent to light. So it's older than the microwave background radiation, which is the oldest thing we see now.

   It's called LISA - the Laser Interferometric Satellite Antenna. And we're in luck: ESA has just decided to launch it in 2034.

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     Dorit (doritc@norden.social)'s status on Sunday, 28-Jan-2024 20:01:29 JST Dorit

     in reply to

     @johncarlosbaez For those understanding German, this podcast episode on the wider topic may be of interest: https://raumzeit-podcast.de/2016/02/18/rz061-gravitationswellenastronomie/ (Tim Pritlove and Oliver Jennrich talking for close to 3 Hours, back in 2016, on astronomy using gravitational waves.)

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     John Carlos Baez (johncarlosbaez@mathstodon.xyz)'s status on Monday, 29-Jan-2024 17:00:00 JST John Carlos Baez

     in reply to

     • Kevin Russell
     • steev hise

     @detritus - No, the decline in US carbon dioxide emissions is not due to COVID. If you actually look at the graph you'll see US carbon emissions have been dropping since 2007, with little wiggles. They've dropped 20% since 2007 - and we expect them to keep dropping!

     There was indeed a plunge during COVID, and it bounced back in 2023. But US carbon dioxide emissions in 2023 were 4,778 megatonnes, down 20% from the peak in 2007, namely 6016 megatonnes. Carbon emissions are expected to drop in 2024.

     Too bad this information isn't more widely known! For data up to 2022 go here:

     https://www.statista.com/statistics/183943/us-carbon-dioxide-emissions-from-1999/

     and for more recent data go here:

     https://www.eia.gov/outlooks/steo/report/total.php

     @kevinrns

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     steev hise (detritus@todon.eu)'s status on Monday, 29-Jan-2024 17:00:03 JST steev hise

     in reply to

     • Kevin Russell

     @johncarlosbaez @kevinrns the little dip in your graph even for US alone is due to covid, most likely. Overall there’s no slowdown in our march toward global doom.

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     John Carlos Baez (johncarlosbaez@mathstodon.xyz)'s status on Monday, 29-Jan-2024 17:00:04 JST John Carlos Baez

     in reply to

     • Kevin Russell
     • steev hise

     @detritus - it's true that *more energy* won't save, only *less carbon emitted*. But the revolution in solar power is having some effects. Carbon emissions are dropping in the US and EU, as even this somewhat old chart shows (that trend is continuing). Unfortunately that trend was overshadowed by China's skyrocketing emissions. So I'd say our future depends a lot on what the Chinese and Indians do.

     @kevinrns

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     steev hise (detritus@todon.eu)'s status on Monday, 29-Jan-2024 17:00:05 JST steev hise

     in reply to

     • Kevin Russell

     @johncarlosbaez @kevinrns but that’s not replacing fossil fuels, just adding to them. That wont save us.

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     John Carlos Baez (johncarlosbaez@mathstodon.xyz)'s status on Monday, 29-Jan-2024 17:00:06 JST John Carlos Baez

     in reply to

     • Kevin Russell

     @kevinrns - I agree with you. When I talk about the collapse of civilization I'm talking about climate change. But if we could break free from the grip of the super-rich we could tackle that. Already last year we added 50% more renewable energy last year than the year before. China added enough solar to power more than 50 million homes.

     What's that country smaller than Cuba?

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     Kevin Russell (kevinrns@mstdn.social)'s status on Monday, 29-Jan-2024 17:00:08 JST Kevin Russell

     in reply to

     @johncarlosbaez

     Science is exponential, tech and human support is exponential. The growth in economic capacity since WW2 is exponential. 14 people make half a million tons of steel a year. A country smaller than Cuba is the 2nd largest exporter of food. Wealth is available to every human, denying it is an intentional crime. Paying living wages would supercharge the economy.

     Humans are emerging.

     Our only crisis is Billionaires are trying to take the new world from us.

     #Climate #poverty

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     John Carlos Baez (johncarlosbaez@mathstodon.xyz)'s status on Monday, 29-Jan-2024 17:00:12 JST John Carlos Baez

     in reply to

     • Archnemysis

     @Archnemysis - Not 38 seconds, 10⁻³⁸ seconds. As others have said in different ways, that means the gravitational background radiation was released about 0.0000000000000000000000000000000000000001 seconds after the Big Bang! Check out my timeline of the very early history of the Universe to put this in context:

     https://math.ucr.edu/home/baez/timeline.html#bang

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     Archnemysis (archnemysis@mastodon.social)'s status on Monday, 29-Jan-2024 17:00:14 JST Archnemysis

     in reply to

     @johncarlosbaez Numbers on this scale break my brain. Is that last sentence saying, basically, 38 seconds after the creation of the universe?

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     John Carlos Baez (johncarlosbaez@mathstodon.xyz)'s status on Monday, 29-Jan-2024 17:00:15 JST John Carlos Baez

     in reply to

     • Tom Richardson Ph. D.

     @CascadeTommy - I've been amazed by this experiment ever since I heard about it. Back in 1999 I wrote this:

     "The idea is to orbit 3 satellites in an equilateral triangle with sides 5 million kilometers long, and constantly measure the distance between them to an accuracy of a tenth of an angstrom - 10⁻¹¹ meters - using laser interferometry. The big distances would make it possible to detect gravitational waves with frequencies of .0001 to .1 hertz, much lower than the frequencies for which the ground-based detectors are optimized. The plan involves a really cool technical trick to keep the satellites from being pushed around by solar wind and the like: each satellite will have a free-falling metal cube floating inside it, and if the satellite gets pushed to one side relative to this mass, sensors will detect this and thrusters will push the satellite back on course.

     I don't think LISA has been funded yet, but if all goes well, it may fly within 10 years or so. Eventually, a project called LISA 2 might be sensitive enough to detect gravitational waves left over from the early universe - the gravitational analogue of the cosmic microwave background radiation!

     The microwave background radiation tells us about the universe when it was roughly 10⁵ years old, since that's when things cooled down enough for most of the hydrogen to stop being ionized, making it transparent to electromagnetic radiation. In physics jargon, that's when electromagnetic radiation "decoupled". But the gravitational background radiation would tell us about the universe when it was roughly 10⁻³⁸ seconds old, since that's when gravitational radiation decoupled."

     https://math.ucr.edu/home/baez/week143.html

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     Tom Richardson Ph. D. (cascadetommy@c.im)'s status on Monday, 29-Jan-2024 17:00:16 JST Tom Richardson Ph. D.

     in reply to

     @johncarlosbaez let me be the second “Wow!”

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     gnarf (gnarf@hachyderm.io)'s status on Monday, 29-Jan-2024 17:00:24 JST gnarf

     in reply to

     • Tom Richardson Ph. D.

     @johncarlosbaez @CascadeTommy

     "..may fly within 10 years"

     Sigh, that hurts a bit. I recently spoke with some frustrated mission planners at ESA. It appears that juggling budgets, 22 member states and the scientific community seems to be quite the thankless job.

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     John Carlos Baez (johncarlosbaez@mathstodon.xyz)'s status on Monday, 29-Jan-2024 21:07:51 JST John Carlos Baez

     in reply to

     • Jon W

     @jw4ke - I used to work on quantum gravity and particle physics. Now I'm trying to work on epidemiology and carbon emissions, since I don't feel I have luxury to whatever I enjoy.

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     Jon W (jw4ke@mstdn.social)'s status on Monday, 29-Jan-2024 21:08:00 JST Jon W

     in reply to

     @johncarlosbaez This kind of stuff used to really excite me before our recent leaders decided that human civilization should end in 7 generations or so. So what’s the point of acquiring more knowledge now? Let’s just spend our time and money mitigating the suffering that is coming.

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     Steve Dodge (jsdodge@fediscience.org)'s status on Monday, 29-Jan-2024 21:08:04 JST Steve Dodge

     in reply to

     @johncarlosbaez
     I remember the laser physicist Bob Beyer talking about this project in the 90s, when LIGO was still under development (some of it in a lab that I shared with a mechanical engineer who was designing vibration isolation for the LIGO mirror supports). Even LIGO seemed a bit crazy to me at the time, and LISA seemed completely absurd. It’s exciting to see it gain traction! Fingers crossed our civilization doesn’t collapse before it launches…. 😬

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     John Carlos Baez (johncarlosbaez@mathstodon.xyz)'s status on Monday, 29-Jan-2024 21:08:08 JST John Carlos Baez

     in reply to

     • Steve Dodge

     @jsdodge - in aome ways it's less absurd to do this in space. LIGO is so sensitive it detects logging in nearby forests.

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     John Carlos Baez (johncarlosbaez@mathstodon.xyz)'s status on Monday, 29-Jan-2024 21:08:10 JST John Carlos Baez

     in reply to

     • Dom

     @dom - we don't laugh at Neolithic stone circles like Stonehenge. At least I don't. I find them impressive.

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     Dom (dom@mstdn.ca)'s status on Monday, 29-Jan-2024 21:08:11 JST Dom

     in reply to

     @johncarlosbaez Sorry but WE should be proud of our own technological and scientific development. An alien civilization arriving here after travelling light-years would laugh at our low understanding of the universe.

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     clacke (clacke@libranet.de)'s status on Monday, 29-Jan-2024 21:08:14 JST clacke

     in reply to

     • Dom
     @dom @johncarlosbaez As a human, if we'd advance to interstellar flight in a couple of centuries and we'd go visit some previously inhabited planet, when we'd see the stuff they built before they perished, I don't we'd laugh. I think we'd recognize ourselves in part of it, marvel at the stuff we didn't recognize from our own history, and be sad that they're gone so we can't talk to them and compare notes.
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     Dom (dom@mstdn.ca)'s status on Monday, 29-Jan-2024 21:08:15 JST Dom

     in reply to

     @johncarlosbaez I don't think you guys are actually reading my comments.

     HUMANS can marvel at our own past and how we developed over time (acknowledging both our past amd present endeavours) but ALIENS (if they were able to come here, hence able to overcome light-years of distance) would not find us special at all because we're a very self-destructive species.

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     phiofx (phiofx@hachyderm.io)'s status on Tuesday, 30-Jan-2024 05:06:31 JST phiofx

     in reply to

     @johncarlosbaez so far gravitational wave detection and black hole astrophysics do not seem to change our (broad brush) views on gravity and cosmology. Is there a chance that LISA will actually shake things up a bit (or a lot)?

     Aka, our civilization collapsed, but for a brief moment our silly putty brains reflected the true nature of the Universe...

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     Richard Hendricks (hendric@astronomy.city)'s status on Tuesday, 30-Jan-2024 12:10:42 JST Richard Hendricks

     in reply to

     • clacke
     • Dom

     @clacke @johncarlosbaez @dom https://www.baen.com/Chapters/0743498747/0743498747___1.htm

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     clacke (clacke@libranet.de)'s status on Tuesday, 30-Jan-2024 12:11:47 JST clacke

     in reply to

     • Dom
     • Richard Hendricks
     @hendric @dom @johncarlosbaez What a wonderful read! I got through 25% of it last night and will continue tonight.
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     Richard Hendricks (hendric@astronomy.city)'s status on Tuesday, 30-Jan-2024 23:43:22 JST Richard Hendricks

     in reply to

     • clacke
     • Dom

     @clacke @johncarlosbaez @dom Just remember, this is the old magics, it isn't derivative, everything else is a derivative of it.

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     John Carlos Baez (johncarlosbaez@mathstodon.xyz)'s status on Thursday, 01-Feb-2024 12:10:03 JST John Carlos Baez

     in reply to

     • Daniela B 🇵🇸 🌏🌱💦

     @dbattistella - we're similarly impressed by the stone heads of Easter Island: they died out after they cut down all the trees on the island.

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     Daniela B 🇵🇸 🌏🌱💦 (dbattistella@mstdn.ca)'s status on Thursday, 01-Feb-2024 12:10:04 JST Daniela B 🇵🇸 🌏🌱💦

     in reply to

     @johncarlosbaez “They scorched their planet and genocided themselves out of existence, but look how smart they were!”

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     John Carlos Baez (johncarlosbaez@mathstodon.xyz)'s status on Thursday, 01-Feb-2024 12:10:09 JST John Carlos Baez

     in reply to

     • phiofx

     @phiofx - LIGO changed our views on astrophysics: it turns out there are lots of black holes 30-60 times the mass of our Sun, and we still don't where they came from. But not our views on gravity or cosmology. LISA, on the other hand, may measure the gravitational background radiation, which was produced about 10⁻³⁸ seconds after the Big Bang! This probes a realm we've never accessed before, and it could shed new light on quantum gravity.

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     John Carlos Baez (johncarlosbaez@mathstodon.xyz)'s status on Thursday, 01-Feb-2024 12:10:12 JST John Carlos Baez

     in reply to

     • Peter Jakobs ⛵

     @pjakobs - I agree: humanity has enormous potential, we're our own worst enemy but we need to keep in mind how great we can be.

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     Peter Jakobs ⛵ (pjakobs@mastodon.green)'s status on Thursday, 01-Feb-2024 12:10:14 JST Peter Jakobs ⛵

     in reply to

     @johncarlosbaez we need these projects, they make us see how we are capable of doing our best in times when there's not a huge amount of that going on.

     Thank god it's science! ;-)

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     John Carlos Baez (johncarlosbaez@mathstodon.xyz)'s status on Thursday, 01-Feb-2024 12:10:16 JST John Carlos Baez

     in reply to

     • Roger Lancefield

     @roger - or maybe they'll have survived an era where they, too, needed to change to take responsibility for their ecosystem.

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     Roger Lancefield (roger@social.ralnode.net)'s status on Thursday, 01-Feb-2024 12:10:26 JST Roger Lancefield

     in reply to

     @johncarlosbaez It is indeed as awesome as awesome gets. One suspects that those extraterrestrial, future archaeologists will be utterly baffled as to how such a civilisation was able to create such technology, but yet was incapable of maintaining the conditions required for life on their own planet.

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     Brahn (brahn@hachyderm.io)'s status on Tuesday, 20-Feb-2024 16:36:14 JST Brahn

     in reply to

     @johncarlosbaez gold cubes with friggin lazers

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     clacke (clacke@libranet.de)'s status on Tuesday, 20-Feb-2024 16:36:17 JST clacke

     in reply to
     @johncarlosbaez "We believe the ancients used this fine-tuned apparatus to monitor celestial events. It is far more advanced than anything else we've found preserved and goes against what we have assumed so far about their level of sophistication. Some say they could not have built it themselves and must have had help from visitors from another star system."