ctrl_alt_scifiFeb 11, 2024
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 2.5 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. These gravitational waves were created before the hot gas in the Universe cooled down enough to become transparent to light. So they're 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 2035.

Jan 27, 2024 at 6:22pmWeb
Show threadMarco 🌳 ZoccaJan 27, 2024
@johncarlosbaez wow that's so cool!
Show threadTom Richardson Ph. D.Jan 27, 2024
@johncarlosbaez let me be the second “Wow!”
Show threadJohn Carlos BaezJan 27, 2024

@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

week143

Show threadArchnemysisJan 27, 2024
@johncarlosbaez Numbers on this scale break my brain. Is that last sentence saying, basically, 38 seconds after the creation of the universe?
Show threadJohn Carlos BaezJan 27, 2024

@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

timeline

Show threadgnarfJan 27, 2024

@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.

Show threadJohn Carlos BaezJan 28, 2024

@gnarf - it's a very tough job. But the spacecraft do eventually fly... some of them, at least.

@CascadeTommy

Show threadRevK Jan 29, 2024
@johncarlosbaez @CascadeTommy now I understand, so the gold cube is inside in a vacuum so that it does not get pushed around? And the outside is steered to keep it in the middle. Just hope it does not touch the sides!
Show threadJohn Carlos BaezJan 29, 2024

@revk @CascadeTommy - the satellite is steered around so the 2 gold cubes floating inside it do not touch the walls of the vacuum chamber. The cubes are in free fall. The satellite is *almost* in free fall - it's just very gently pushed by solar wind - so it only needs tiny thrusters to make very gentle course corrections that keep the cubes where they belong. This technology has been tested by LISA Pathfinder, and it worked.

https://spacenews.com/lisa-pathfinders-success-boosts-likelihood-of-future-gravity-wave-observatory/

Lisa Pathfinder's success boosts likelihood of future gravity-wave observatory

European scientists on June 7 said the Lisa Pathfinder technology-demonstrator satellite, launched in December to determine if current technologies were sufficient to justify investment in a full-scale gravitational-wave observatory, has far surpassed expectations and should lead to a larger mission around 2034.

SpaceNews
Show threadJohn ManuelApr 26, 2024
@johncarlosbaez ESA's GOCE mission was also a pathfinder for LISA. It successfully zeroed out the atmospheric drag it felt as it "flew" through the thermosphere. This enabled its gravity gradiometer to make ultrasensitive measurements of the Earth's gravitational field, so sensitive that, in combination with good satellite altimetry data, it was able to map deep ocean currents. https://www.esa.int/esapub/bulletin/bulletin133/bul133c_fehringer.pdf
Show threadJohn Carlos BaezApr 26, 2024
@evanescent - Nice!
Show threadAdlangxJan 27, 2024
@johncarlosbaez Humans are kinda rad.
Show threadJohn Carlos BaezJan 28, 2024
@lightninhopkins - we have a lot of potential.
Show threadabby! you're being melodramatic (ITAR Compliant) 🏳️‍🌈🏳️‍⚧️Jan 27, 2024
@johncarlosbaez let's hope lack of funding and bureaucracy don't kill it 🤞🏻🤞🏻🤞🏻
Show threadNico Jan 27, 2024
@johncarlosbaez If???
Show threadLes capsules du prof LutzJan 27, 2024

@johncarlosbaez «If our civilization collapses, extraterrestrial archaeologists can look at this and be impressed. »

No. They'll get confused: «How a specie with so much technical knowledge could go instinct by killing their own ecosystems? Didn't they know? If only we made contact earlier» - 👽 (Google translated)

Show threadScruffy looking packet herderJan 27, 2024
@johncarlosbaez @lutzray You might be interested in reading A Half Built Garden.
Show threadLes capsules du prof LutzJan 27, 2024
@sng Thx. Funny: I'm reading Ursula K. Le Guin and this link https://us.macmillan.com/books/9781250856104/ahalfbuiltgarden presents Ruthanna Emrys as a literary descendent of her.
A Half-Built Garden

A literary descendent of Ursula K. Le Guin, Ruthanna Emrys crafts a novel of extraterrestrial diplomacy and urgent climate repair bursting with quiet, tenuou...

Macmillan Publishers
Show threadScruffy looking packet herderJan 27, 2024
@lutzray She very much is a spiritual descendant of Le Guin, yes.
Show threadLes capsules du prof LutzJan 30, 2024

@sng C'est particulier, depuis que j'ai commencé à la lire, je la vois partout...🤔

I just donated to the project https://en.goteo.org/project/who-is-afraid-of-degrowth where the drawing comes from.

Who Is Afraid of Degrowth?

A Graphic Novel About the Misunderstandings of Degrowth

Goteo.org
Show threadScruffy looking packet herderJan 30, 2024
@lutzray Oh having unlimited access to her books at the library totally radicalized me.
Show threadJohn Carlos BaezJan 28, 2024
@sng @lutzray - what is that book about?
Show threadScruffy looking packet herderJan 28, 2024
@lutzray @johncarlosbaez Aliens show up to try to save us from ourselves and stuff happens. See also “Rejoice, A Knife To The Heart”.
Show threadKevin RussellJan 27, 2024

@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

Show threadJohn Carlos BaezJan 27, 2024

@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?

Show threadKevin RussellJan 27, 2024

@johncarlosbaez

Its also the largest exporter of flowers in the world, it has schools, theatres, railways, universities, ports, warehouses, manufacturing, daycares, shipping, literature, homes, shipbuilding and it uses less electricity than the crypto scam which produces nothing but crime.

It is 25% switched to wind and sun, so far.

Show threadBob JonkmanJan 28, 2024

Mind blown: Cuba is a huge country compared to the Netherlands:

Cuba: 110,860 km²
Netherlands: 41,865 km²

(via Wikipedia)

Where were all the practical geography lessons when I was in school?

@kevinrns @johncarlosbaez

Show threadKevin RussellJan 28, 2024

@bobjonkman @johncarlosbaez

We need a bigger country they said.

Show threadThe Lunatic DreyfusJan 27, 2024
@johncarlosbaez This is very impressive.
Show threadAviva GaryJan 27, 2024
@johncarlosbaez This is so cool
Show threadJon WJan 27, 2024
@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.
Show threadJohn Carlos BaezJan 27, 2024
@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.
Show threadSteve DodgeJan 27, 2024
@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…. 😬
Show threadJohn Carlos BaezJan 27, 2024
@jsdodge - in aome ways it's less absurd to do this in space. LIGO is so sensitive it detects logging in nearby forests.
Show threadSteve DodgeJan 27, 2024

@johncarlosbaez
Absolutely — but I’m a tabletop experimentalist, so the thought of working out all of the details *before launch* is a bit terrifying!

(cf Hubble mirrors, same era)

Show threadj_bertolottiJan 28, 2024
@jsdodge
Yes, my usual approach of "let me put on the table a bunch of optics and fiddle with them until I figure how to change them to make the experiment work" is unlikely to work particularly well here 😉
@johncarlosbaez
Show threadPaul RebmannJan 27, 2024
@johncarlosbaez this is so beyond me, but it sounds really cool!
Show threadBashStKidJan 27, 2024
@johncarlosbaez This is very cool. And it would be interesting to have a sensitive low-energy experimental test of Mach's Principle.
Show threadrebel_without_a_pauseJan 27, 2024
@johncarlosbaez ..."if" will happen the rest is just hoping...
Show threadrebel_without_a_pauseJan 27, 2024
@johncarlosbaez 2034? Trying to look smart is the entire reason we are here at the destruction of our heaven on Earth. We do not even know a minuscule amount our own planet.
Show threadBen ZaninJan 27, 2024

@johncarlosbaez yoooooo @rjay 👀↑↑ ∆🛰️

EQUILATERAL SPACE LASERS
FOR SCIENCE

Show threadKlaus Vink SlottJan 27, 2024
@johncarlosbaez
A friend of mine told me about this project years ago, he was working as an engineer at a company giving a bid on some part of the setup. I was 🤯 about the proportions, the accuracy and what this project will try to achieve.
@liebach
Show threadGreg EganJan 28, 2024

@johncarlosbaez

Typo: it’s 2.5 million km separation, not 25 million km.

It’s kind of sad that the operational lifetime of LISA is only expected to be 4 to 6 years.

Show threadJohn Carlos BaezJan 28, 2024

@gregeganSF - I wonder what will spell the end of LISA. The satellites do need propellant to stay on course. The proof-of-concept mission LISA Pathfinder used "micronewton thrusters" that shot out cold gas.

https://scholar.archive.org/work/5r3qrbxxwrb7ldvwipahnws7cu/access/wayback/https://www.zora.uzh.ch/id/eprint/175976/1/PhysRevD.99.122003.pdf

Show threadLeo C. SteinJan 28, 2024
@johncarlosbaez @gregeganSF Spacecraft engineers have a tendency to do such a good job that their consumables often get stretched by factors of 2 or more!
Show threadgermanioJan 28, 2024

@johncarlosbaez wow!

ok ok, you won the first price as the best description someone could do of anything.

now I can't wait for LISA to be up and running!

Show threadDoritJan 28, 2024
@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.)
RZ061 Gravitationswellenastronomie

Über die Entdeckung und Zukunft der Gravitationswellenastronomie Lange Zeit waren Gravitationswellen nicht viel mehr als eine Voraussage der Allgemeinen Relativitätstheorie von Albert Einstein. Doch wie so viele andere Details dieses Meilensteins der Wissenschaft konnten nun auch diese speziellen Eigenschaften des Universums experimentell nachgewiesen werden. Eine seit Jahrzehnten engagiert und global arbeitenden Community von Wissenschaftlern hat hartnäckig an Meßmethoden gearbeitet und diese ein ums andere Mal verbessert und dabei Meßgenauigkeiten erreicht, die einem schon absurd vorkommen können. Doch nun wurden nicht nur die Wellen entdeckt: zugleich wurde das energetischste Ereignis gefunden, dass je von einem Menschen im Universum beobachtet wurde. Und nur diese Methode hatte überhaupt die Chance, zwei Schwarzen Löchern beim Aufeinandertreffen zuzuschauen. Damit öffnet die gelungene Messung nicht weniger als das Tor zu einer komplett neuen Form der Weltraumbeobachtung: der Gravitationswellenastronomie.

Raumzeit
Show threadJohn Carlos BaezJan 28, 2024
@doritc - thanks!
Show threadaevaJan 28, 2024
@johncarlosbaez it looks like earth is flying a little kite :D
Show threadhalcy​ Jan 28, 2024
@johncarlosbaez yeah no kidding. We‘re actually entering the „system you come across in a space video game and it gives you a little Wow, Ancient Powerful Civilization type event popup“ stage of building large things
Show threadClive ThompsonJan 28, 2024

@johncarlosbaez

This reminds me of Gravity Probe B, which was (for its time) a similarly awe-inspiring piece of engineering — they had to craft two spheres that were, back then, the smoothest objects humanity had ever produced, then start them spinning eternally to become precise gyroscopic measurements of “frame dragging”, or, the relativistic propensity of the earth to slightly drag and deform the shape of spacetime around it as it rotates

Love projects like this so much

Show threadClive ThompsonJan 28, 2024

@johncarlosbaez

(I strongly suspect you know more about Gravity Probe B than I do 😅)

Show threadFrosch BJan 28, 2024

@johncarlosbaez oh ich freue mich schon so drauf!

Andererseits fürchte ich aber auch, dass in den 30ern die Klimakatastrophen-induzierten Konflikte in großer Zahl aufkommen und in die heiße Phase übergehen werden, also sehr unklar ist ob dann noch Zeit und Ressourcen für so etwas aufgebracht werden

Show threadFelix B. OhmannJan 28, 2024

@johncarlosbaez

a: yeah, wow, can't wait to "see" this in action.

b: I imagine the extraterrestrial archeologists will have this technology in their "mobile computers"/"phones" and be like: ah yeah, THAT phase of development with all the carbon-based rockets and the deadly debris shield in orbit... ;)

Show threaddojoeJan 28, 2024
@johncarlosbaez This is the stuff of SciFi stories where explorers discover technology of a lost civilization and are utterly befuddled, never finding out what it means and feeling lost, alone and insignificant as a result.
Show threaddojoeJan 28, 2024
@johncarlosbaez (I am thinking of Limiting Factor by Clifford D. Simak, a story that deeply impressed me in my youth.)
Show threadTitoJan 28, 2024
@johncarlosbaez the problem would came when they put feet on earth and get a conclusion of mankind collapse.
Show threadun_pogazJan 28, 2024

@johncarlosbaez At what point are we able to have precise trajectories orbite?

^ this shit.

Show threadanlomedadJan 28, 2024
@johncarlosbaez
Awesome toot!
When you said, lasers were bouncing between the gold cubes, I thought: there, that's those flashes, those stellar thunderstorms that can sometimes be seen in deep space, eons away. Other civilisations were/are detecting gravitational waves!
🙋‍♀️