Strange Isotopes in Supernovae, External Gravitational Lenses, Existence of The Present | Q&A 228

Which astronomical events can only be seen with gravitational waves? Is there enough water on the Moon for a permanent colony? Can we use stars other than the Sun as gravitational lenses? Does the present even exist or are we always living in the past? All this and more in this week's Q&A session.
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00:00 Start
00:40 [Tatooine] Which things we can see only with gravitational waves?
10:38 [Coruscant] How can the Universe be larger than 13.8 billion light years?
13:26 [Hoth] Are we all living in the past?
16:04 [Naboo] How's the search for Planet 9 going?
18:57 [Kamino] Are there rare elements on Mars?
20:34 [Bespin] Is there enough water on the Moon for a permanent colony?
22:11 [Mustafar] Can we use other stars as gravitational lenses?
25:01 [Alderaan] Are strange isotopes and rare elements created in supernovae?
27:01 [Dagobah] Worst space-related movie regarding Physics?
28:49 [Yavin] Do gas giants have solid cores?
29:59 [Mandalore] What would I do if I met aliens?
33:29 [Geonosis] What would I do as a NASA Chief?
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[@lucashouse9117]

I think the most depressing thing about having cancer is the thought that I won't live long enough to see all the things we could discover during what my life could have been. Oh well maybe if I do die I'll get to see all the answers. I love your channel. It keeps me going. So thank you for all you do.

[@nandesu]

There are many amazing new cancer therapies coming. From Turkey Mushroom therapies (research Paul Staments) to new MRNA cancer vaccines. Don’t give up. Just try and survive and make it your mission to participate in these new studies. Good luck.

[@frasercain]

Here's hoping the therapies come so quickly that cancer becomes another disease that we manage. Then we'll both watch the end of the Universe in our robot bodies.

[@codyramseur]

It’s always a nice trickle of serotonin that happens whenever I hear “It’s time for the Question Show.” Ever since I discovered Astronomy Cast several years ago and then eventually your work on KZbin, you have easily become my favorite science communicator on the topic of space. Hooray Fraser!

[@BoechaarBiets]

sounds like you dont know anton petrov 😜

[@codyramseur]

@@BoechaarBiets I love Anton! I’d rank him as a very very VERY close second.

[@runningray]

Coruscant! I love that question blowing my mind every time it comes up.

[@marcomattano3705]

I love Culture's ship names! My favorite Culture book is "The Player of Games (1988)", but I highly recommend two non-Culture Banks titles: "The Algebraist (2004)" and the more obscure,, amazingly creative, multiverse spy thriller "Transition (2009)" that would be my first choice for a Banks book movie adaptation.

[@ashnur]

Best name is "Mistake not ..."

[@t0kinicnak]

The Algebraist is amazing, Love those dwellers and their quest for kudos

[@ruspj]

tried the ExForce series? the Jeraptha ship names are great especially those controled by Uhtavio(Sketchy mc sleeze ball)Scorandum of the ECO names like "We Were Never Here" "Will Do Sketchy Things" and "Plausible Deniability"

[@ashnur]

@@ruspj Definitely some banksian influence in those names:)

[@marcomattano3705]

@@ashnur Serious Callers Only

[@MCsCreations]

Yavin! Thanks a bunch for all the answers, Fraser! 😊 Stay safe there with your family! 🖖😊

[@apm9475]

The present exists , until it becomes the past. And when it's becomes the past , it's is either a personal memory or simply history.

[@alphanaut14]

Alderaan- If you expand the reach of the question to minerals instead of just elements, you get tens of thousands of possibilities. The presence of CuIII in a SiCuO mineral can make it's properties completely different the CuIV. Valence electrons count. We are routinely finding minerals in meteorites that have never been discovered on Earth. You don't have to get into the realm of high proton counts to find exotic materials.

[@ashnur]

(Kamino) I think the whole Mars colonization question is a red herring because people don't want to be loud about trying to be the first to bring home some metallic asteroids, but there is no effing way whatsoever that some company on Earth that can keep humans alive for years on the surface of Mars, wouldn't try to first deal with the easier challenge to mine an asteroid, at least as a proof of concept.

[@how2pick4name]

I just realized that we are technically the center of the universe. :D

[@cavetroll666]

Thanks Fraser have a good week 🙃

[@robertmason5676]

excellent explanation . Coruscant

[@Disasterina]

Fraser! Love the show! I vote: Bespin! Also, why do we know more about Trappist-1 planets than Alpha Centauri’s planets?

[@1112viggo]

I like how you describe the sound of the most massive and powerful objects in the known universe colliding as "a chirp" I guess the seize is even more mind-blowing than the energies at work in the universe. God damn.

[@joankx2cw425]

Thank you, again!

[@mikemontgomery8407]

Great show 👊

[@eonuzex]

reminds me that I had this crazy idea/thought experiment that the expansion of the universe is what gives us time or at least the direction of time.

[@sakaeagaga4229]

wonderful show

[@ashnur]

Sci-fi is not even about aliens, just look at Asimov's writings :D

[@mihan2d]

Well yeah ever heard of one little known franchise named Dune? Or there are sci-fi settings which are set almost completely on Earth like Horizon series or Cyberpunk

[@nevyngould1744]

Asimov virtually got his chemistry degree on the strength of a paper about a material that doesn't exist, a paper written for a joke that the examing board was never supposed to see. They got hold of it the day before he was to present. I have this in his own words, in an anthology of his short stories.

[@NoX-512]

You are right about that. Science fiction has nothing to do with aliens. It just happens that many Sci-fi authors use aliens in their stories. The Martian is also a good example.

[@btjr583]

Geonosis. What a great answer! Is it possible that there is no singular big bang that occurs (at one time encompassing everything, perhaps re-acurring in a cycle) but multiple big bangs throughout multiple locations and times? For example, throughout each super-cluster. If this is possible, then the Great Attractor or Shapley Attractor could be an evolving singularity forming independent of the greater void? Sorry if the wording is somewhat crude however I hope you get a grasp of the question. Love your work and love your opinions and congratulations on such a fine channel

[@zimmy1958]

Thanks

[@mihan2d]

27:01 It's gotta be Fast and Furious franchise 🤣🤣

[@lgme378]

For black holes or neutron stars fusion, it’s only the few last seconds that emits the waves that are detected. It’s weak because it happened far far away and it faded away.

[@arlisnarusberk]

thank you

[@samson1200]

I love the work you do. It is very good and well researched with knowledgeable guests for current knowledge' I would like to know if there has been research to find the maximum number of organisms that the Earth can sustain? Kamino.

[@datsmay]

Hi Fraser, Love your channel. Keep up the good work. Why is it so hard to orbit the planet Mercury?

[@brianfunaiole1871]

I like this question - it’s answer is an amalgamation of being hard to get that close to the sun, and relativistic effects when you’re that deep in the sun’s gravity well. Would love to hear this as a topic.

[@nicodesmidt4034]

On Coruscant: this postulates that the expansion of the universe was equal across the 13B years. That might not necessarily be true

[@NullHand]

All our observations point to it not being equal. It has been speeding up these latter 4 billion years or so, and by the smoothness of the CMB ( as well as the fact that we see matter that isn't already in a black hole) we can infer that space was expanding at a hella fast pace early in the Universe. Fast enough to effectively cancel gravity everywhere. Sometime in between gravity seemed to be evening the score a bit, but it's lost the game already for most all the stuff we can see. We will probably get to keep the Local Group.

[@pablohsfranco]

I liked the video :) 13:30 Does this mean that if we find a Type 2 Kardashev Scale civilization that is 1 Billion years away in some galaxy, then it could be that they are already Type 3 Kardashev Scale because we are seeing the past? 🤔

[@steve9007]

Give a type 2 a billion years then I would expect a type 4 or beyond.

[@daviddunmore8415]

I've read all the Culture series, when you get there, my favourites are 'Matter' and 'Surface detail' I'd be interested in your thoughts on those two books.

[@Qrul]

Coruscant. Question: When we look at an object and calculate' as correctly as possible, that it is e.g. 15 billion light years away. We know that it is farther than that now because of expansion, but is it considered as that light travels here because the expansion is on going as the light travels, If that is considered, then wasn't the object actually closer to us when that light was sent, due to the 15 billion years of expansion during it's travel? I hope I conveyed my question competently.

[@lenwhatever4187]

Bespin: Any question about water on The Moon should also consider that a well designed habitat will not "use up" water so that it "runs out" because it will be recycled... At least if it is only used as water. (even a less well designed habitat will keep water inside) However, other uses of water's components such as oxygen to breath, Hydrogen as fuel (or even as a by product of making "air") will make it harder to keep it from escaping. Then there is the idea to use water as rocket fuel at which point it becomes a resource that will run out. Water for use as rocket fuel is finite. Water as used for life support may be effectively constant as it seems to be collecting still. So there would be a balance between how much is lost and how much is replenished. When more is used for things like rocket fuel than is naturally collected, commit capture starts to look good.

[@NullHand]

Oxygen to breathe can be had from moon rocks. Probably as a byproduct of reducing FeO2 to iron or Al2O3 to aluminum. About 45% of the rock surface of the moon (and Earth) is oxygen. It's the hydrogen that is really scarce on the moon.

[@extropian314]

13:00 Hey Frasier, I thought of a fresh way of explaining this that might reach some people: If we're watching a basebal player hit the ball and the start running, we see his light instantly. If the speed of light were slower, say 10 mph, then by the time his light reached us, he'd already be on third base. Just like the galaxies moving.

[@paulwilson6511]

Let's think about gravitational waves being responsible for the expansion rate of the universe / dark energy. Space-time is certainly expanding then shrinking through the waves. But maybe they leave a permanent impact on space-time. There was a recent paper that tied the expansion rate(s) over time to the growth of supermassive black holes over time. And supermassive black hole mergers would be the source of the biggest gravitational waves. Whatever happens, at least we know there really is something / a fabric of space-time that can be stretched and shrunk by gravitational waves. Faster than light travel possibilities for example but maybe it takes way too much energy to expand/shrink space-time.

[@user-bs1lr8nx1h]

Can Ligos arm be even longer ? or are Earth curvature to big for that ?

[@ejrupp9555]

So space between point a and b expands as a function that is slower than the speed of light function? But only in certain spots in the universe where there is more dark matter?

[@EdisonDiBlasi]

(Dagobah) Totally agree! It needs to be a good story. I was watching the Mandalorian with friends and we got to the spaceship scene with baby yoda pushing buttons. Someone yelled, "Awww, he's a single dad!!!"

[@billmilosz]

Can you do dark matter astronomy with gravitational waves?

[@KarelGut-rs8mq]

No. You can only use gravitational waves to tell you about whatever caused the gravtational waves in the first place.

[@MrPeter35813]

are gravitational waves redshifted like light from the expansion of the universe? if so, is there a shrinking horizon for the gravitational wave observable universe? Tattoine

[@stuartreed37]

I like that you keep coming back to some fundamentals because it is quite confusing to me and probably most people. For example I get the light travel distance vs actual distance thing. But how does light coming from ancient times reach us when we were there too at the time? Light is faster than matter travelling through space so how do we get here first and then the ancient light gets here? Wouldnt it be far past us? Anyway thanks for helping me slowly build my understanding one piece at a time 😂

[@KempPlays]

It depends where the light is coming from and where "there" is but there's probably a few different factors contributing. Some key ones are probably that 1) we weren't actually there exactly (how close to each other is "there"?) and 2) the distant universe is expanding away from us at faster than the speed of light. Note: objects are not moving through space faster than light, space itself is effectively expanding faster than light... a thing that only exists within the space. It's complicated.

[@RochelleHasTooManyHobbies]

You are correct in saying we were also there with them! But we have ALSO moved! Imagine for a moment that instead of eyes, your vision required a camera with a 10 second delay. And now, walk backwards while someone next to you walks forward. As you are walking, you will see them as they were 10 seconds ago, yes. But also where YOU were 10 seconds ago! So at each viewing point, by the time you get the information the distance between you and your partner has increased 2-fold, once for their distance walked and once for your distance walked backward. Now imagine that instead of starting next to eachother, you and your walking buddy started 2 lightyears apart. Now your camera seems like it has a delay of 2 lightyears and 10 seconds. But your walking buddy has kept walking in that time, and so have you, so the delay keeps getting longer and longer and longer. You are now permanently seeing them in a distant past, and the longer this goes on, the more true that is. Does that make sense? The ancient light was closer to where we were a million years ago, but we've been running away from it at the speed of the expansion of the universe.

[@charleslivingston2256]

We weren't at the same point as them when the light left. The density was very high at the time of the Big Bang. The whole universe was a hot plasma, like one giant, hot star. It expanded quite rapidly; the current observable universe expanded from something close to a point to over a light year in diameter in less than a second. As it expanded, it cooled down. It took about 380,000 years of expansion before it cooled down enough for the electrons and protons to combine to form neutral atoms (about the temperature of a red dwarf star). It's radius was about 2.7 B lightyears It was at this time that it became transparent to light. The cosmic microwave background that we see has been traveling for about 13.4 Byr. At the time that it was emitted, it was about 2.7 B light-years away from us.

[@DrDeuteron]

The Island of Stability is a relative thing. It means a sort of long 1/2 life vs a nuclear resonance, which decays in 10^-20 seconds.

[@NullHand]

Glad someone else hunts down the numbers to that crazy name for hypothetical periodic table expansion. Gives me the hives whenever someone floats that as an explanation for promethium in Przybylski's star.

[@PestOnYT]

[Tatooine] Q: Due to spacetime being curved we know that on earth time is ticking slower than in orbit (GPS time correction etc). However, I was wondering if there's any place (far away from any mass) that we could use as reference point (time dilation factor 1.0) and from there figure out our factor on earth (lower due to earth, solar system, galaxy, local group, etc.)? Furthermore, we are moving at 650 km/s (depending on who you ask) through space relative to CMBR. That also slows down our clocks compared to a reference point. So all measurements made on earth need to take that into account. As the crisis in cosmology is based on two different ways of measurement, I wonder if the difference is cause by that time dilation factor...

[@stanharrison8046]

I don't understand how arival times of light, and gravity waves (both travelling at the speed of light) help measure the size of the universe. Please explain.

[@hexicola]

You mentioned the island of stability which hasn't been reached by supernovas. It got me thinking are there generations of supernovas in the same way stars are referred to. Would a later population supernova be more likely to have stable heavy elements?

[@KarelGut-rs8mq]

No. The more massive a star is when going supernova the more violent the "explosion" will be and the more neutrons will be emitted and it's the neutrons that make new elements. Stars early in the universe were much, much more massive than they are today and can ever be in the future due to the level of metallicity i.e. the amount of "pollution" they contain. The first generation of stars contained only hydrogen and helium because that's all there was back then and therefore needed much, much more of the stuff before they could contract and become stars. Our sun contains roughly 1.5% of heavy elements and therefore could contract much easier and become a star much faster and thus smaller. Stars forming today contain roughly 2% of heavier elements and will therefore be even smaller than stars that were formed when our star was formed. The universe is progressing towards smaller and smaller stars and therefore to weaker and weaker supernovas and much fewer of them.

[@notmyname327]

I recently found this channel and I'm loving all the videos. I have a question about water in the solar system. I've heard that most (all?) water on Earth came from comets or asteroids, but I thought the asteroids and comets came from the same protoplanetary disk that Earth did. Why do we think water comes from those bodies and wasn't already on Earth when it formed?

[@frasercain]

Earth is too close to the Sun, so any water on its surface would have evaporated into space. We needed a way to replenish Earth's water after its protective atmosphere formed. That's why some astronomers think it was comets or asteroids that delivered it later. But another idea is that Earth didn't lose all its water, and plate tectonics churned it out to the surface.

[@gavinwince]

Serious question - since when did SR or GR allow for faster-than-light neutrinos and gravitational waves?

[@frasercain]

Neutrinos go slower than the speed of light and gravitational waves go the speed of light.

[@gavinwince]

@@frasercain In your video, you state that neutrinos and gravitational waves arrive in detectors prior to light. Further, there is data showing GWs arriving prior to EMF, as observed with GW170817 and GW190425. Also, neutrinos on average travel light speed, so again, how are these not in conflict with SR and GR?

[@frasercain]

I feel like I explain it in the video. The gravitational waves aren't blocked by the stellar material so they escape immediately and arrive first. The neutrinos also escape immediately, but travel a little slower than the speed of light so they arrive next. The light has to make a random walk through the infalling stellar material, so there's a delay to when it can escape into space. It's similar to how photons are created at the core of the Sun but take 100,000 years to random walk into space.

[@gavinwince]

@@frasercain Thank you 🙂

[@moondog6004]

Hi Fraser With regards to the gravitational waves that are released by supernovae or black holes colliding. How does the gravitational waves interact with us. Do we feel a micro pull towards the black holes or does it just pass through us ?

[@frasercain]

It distorts your body, squeezing you and then stretching you. But the amount is imperceptible. But if you were too close to a black hole collision, you'd actually get torn apart.

[@moondog6004]

Is this the way the gravitational waves detector detect gravitational waves

[@frasercain]

Yes, the length of the arms of the detector grow and shrink in a detectable way as the waves sweep over.

[@TheyCallMeNewb]

Mandalore. One might wish that these and other slightly more abstract ideas could make their way into becoming staples of science fiction.

[@Andre-qo5ek]

Wayfarers series by Becky Chambers ... The Long Way to a Small, Angry Planet A Closed and Common Orbit Record of a Spaceborn Few To Be Taught, If Fortunate (i am on book 3 right now myself)

[@ioresult]

Excession is also my favorite. It may very well be my favorite story period. An all powerful civilization scared shitless? Yowza.

[@33DavePaton33]

Tatooine Hey Fraser! I've got an interesting question I think you might like. As you know, low mass stars leave behind a white dwarf which can then go on to produce a type-1a supernova. However, this requires the low mass star to first "die" in a binary system. The thing is, lower mass stars tend to have much longer life spans than high mass stars. So the question is, what is the shortest lifespan of a star capable of producing a white dwarf. Seeing as we use type-1a supernova to measure the expansion of the universe. There must have been a time in the early universe when this type of star explosion didn't yet exist.

[@KarelGut-rs8mq]

Correct. Our sun has a lifetime of roughly 10 billion years and the smallest star to produce the kind of white dwarf that is suitable for producing a type 1a needs to be roughly twice as big as our sun in mass. A star twice the mass of our sun would have a lifespan of maybe around one or two billion years. Type 1a supernovas would not have existed before that time.

[@peteranderson2687]

Question My feeling is that time is only relative to the participant, or observer within that particular reference. We all have different time references depending on what we are doing, where there is no past or future, only the present. Unfortunately, we also need to have a standard time reference that can be shared by everyone to synchronise events appointments, measurements, etc. So, a standard time reference model was invented that allowed us to synchronise ourselves with others. While this model has been successful in a lot of ways, I feel that our understanding of time has been severely limited, and to be honest , I really don't know what time is all about. 9:41

[@Jamelith]

Are gravitational waves effected by the gravity it's moving through?

[@MacAisling]

Mandalore because I created a photo of myself with one of those little plastic aliens (@30:43) in response to a tabloid photo of a 3 legged figure skater.

[@abekip]

Long time listener first time question asker… Q: is it possible that the Earth or other planets might be changing in size? Or have expanded/contracted in size in the past as they cool?

[@NullHand]

Seems Mercury has. It has reverse stretch marks. Shrinkage scarps all over. I think the planetologists put it at about 7km in radius since the crust formed.

[@dannybell926]

I would think that's possible, however the change in mass is so low that's its for all counts nonexistent, unless a huge asteroid hits us. Then we would gain mass while then losing mass from all of the ejectate that reaches escape °V

[@jamesrangi1988]

Would, those wave, catch up, with the bang?

[@AlbertNeu]

Do gravitational get weaker when they pass through matter?

[@NullHand]

In theory, if they deposit any energy, then yes. And they have to deposit some small amount for our detectors to see... But their wavelengths are long, so I bet it takes really big things to couple effectively to. I doubt it would be noticable over the inverse square decay. I think a more productive question is would large chunks of mass/energy cause them to Refract? And could we use that?

[@dsewtz3139]

Mandalore! Because I was still thinking about MIB, thanks to Dagobah: Offer the alien a tissue! A DNA sample should hold up against the skeptics, right? 😂

[@t0kinicnak]

Read Embassytown by China Miéville - A really interesting and originally weird bit of self contained scifi

[@ioresult]

If the Vera Rubin observatory is in the southern hemisphere, are there any plans to build its equivalent in the north?

[@frasercain]

Nope.

[@ioresult]

@@frasercain 😭

[@farrier2708]

There is a term for the mental attitude required when watching Science Fiction. It's called "Suspension of Disbelief". If you can do that, you can ignore the alternative physics and enjoy the imagination of the story.

[@Edward-om8mz]

Why they changed the size of the universe?

[@Jacob-Vivimord]

If there were a COLOSSAL black hole collision, such that the gravitational waves emanated were immense, what effect would that have as it passed through our planet? Or passed through our bodies? (And Tatooine, obviously!)

[@mknochel]

Miguel from Salt Lake asking: Could gravitational waves be gravitationally lensed like light is?

[@frasercain]

Yes.

[@JohnKpl]

Coruscant [Q] Hi Fraser. Our solar system was formed about 4.6 billion years ago from a cloud of gas and dust. It also contained heavy elements that we now find on Earth. And here comes my question. The sun has the greatest gravity. Does this mean that it also attracted these heavy elements? How does this affect its operation?

[@Cyborg_Simon]

hoth. does time actually exist? or is it only a human concept of measure?

[@DrNappers]

Instead of heating the water ice on the moon with heating elements, would it be sufficient to mount parabolic mirrors on the rim of the craters and just use light from the sun to do the heating, essentially for free (other than the crushing the regolith part)?

[@brianbrandt25]

Yes, but if not in a sealed container, it would boil off almost immediately after melting. At very low pressure, the boiling point is the same as the melting point. Look up triple point of water..

[@doncarlodivargas5497]

Gravitational waves move trough the universe, and so do we, would it be possible to measure different speeds of the wave depending on the direction? and in that way calculate the direction of our travel trough space?

[@frasercain]

You could measure the red shift and so determine the direction the source (or you) are traveling in.

[@michaelpatchett6982]

Gravitational waves don’t have mass so they would travel at the speed of light so there wouldn’t be a disparity in the speed of waves. But to ask a question related to don Carlo’s. Would gravitational waves always travel at c, regardless of the observers motion . As in if I could ‘travel at light speed’ relativistic to a gravitational wave would that wave stand still or would the wave carry on travelling at light speed? I assume relativistic rules still apply and on space time diagram the wave would be pointing straight up just like photons But I can’t find any answers online

[@frasercain]

You can measure the change in their wavelength, not a change in their speed.

[@kevinICdesigner1]

THANKS for the lead to acollierastro! She is AWESOME and fearless.

[@frasercain]

Enjoy her channel, she's terrific.

[@stephenwitteveen3542]

There's an analogy conflating the expanding universe with an expanding balloon; at that point, it makes sense. Then the physicist refers to the universe as represented only by the 2D exterior skin of the balloon, not the 3D interior, thus we cannot point to the "centre" of the universe, and my frustration increases just a little bit. If all the galaxies are moving away from each other (I know, its more like the space between them expanding), which is the primary evidence behind BBT, I fail to comprehend why we can't point to the spot in the universe where galaxies would converge. Surely we could draw lines in the 3D directions that each galaxy is travelling, where would the lines converge? Thanks!

[@n-steam]

I think we need to start describing gravity as being caused by energy density, and matter being just another form of energy, to be able to explain dark matter, which might not be matter at all.

[@DJChesley]

Using other stars as a gravitational lens seems like it could still totally work! In fact every star has a continuously shifting focal point that would always be viewable, just shifting. (Scope)-----(star)-----(focal point) with 100 billion stars just in our galaxy, it seems like that's 100 billion focal points continuously moving wildly all around, waiting to have a high speed, hi sensitivity telescope that can snap a photo. Most of the time it will be nothing but statistically speaking every once in a while with that many focal points you might get some high megapixel images of distant objects. With further research it might be possible to even make statistical predictions or view many lenses at a time.

[@DJChesley]

Please respond to this comment directly!

[@stanharrison8046]

What do you think of the recent asertion that a black hole made from all the mass/energy in the universe would have an event horizon the same size as the universe?

[@frasercain]

It's a coincidence.

[@NavarroRefugee]

It's actually not clear that supernova or kilonova could produce elements within the theoretical island of stability. The primary method of nucleosynthesis here is the r-process, and it runs into difficulty with neutron availability as the number on the periodic table goes up. Add to this the fact that the island is generally not predicted to be truly stable, only more stable than the elements around it on the table, and it could be the case that stellar processes can't produce these elements in quantities we can detect, and that what little does get produced decays before it can accumulate to a detectable quantity.

[@Etopirynka]

Lately I've been wondering about the Fermi Paradox. Do you think that it could be possible we found no advanced civilizations (or we haven't been found) because of the speed of light? I mean we've only been sending radio signals for ~150yrs. Detecting - even less. Maybe it's just because they're further away that 150ly? Or do you think they did to their planets what we're doing now and they all died?

[@KarelGut-rs8mq]

It's even worse than that. Ordinary commercial radio doesn't really make it through the atmosphere, it's television on the UHF-band that is the really good signal for transmitting to the universe. That means that the first really good transmissions started in the 1940's and ended when television was digitised a decade or so ago. There is around 70 years of us transmitting our thoughts to the universe in total.

[@Etopirynka]

@@KarelGut-rs8mq I dread to think what kind of content was sent out 😅 racism, sexism, anger, violence... no wonder nobody wants to talk to us 😅

[@onebylandtwoifbysearunifby5475]

@@Etopirynka The first such T.V. broadcast was the opening ceremonies of the Olympics in Germany by guess who... Also, the answer to the Fermi Paradox is that there is no paradox. Simply that information has been withheld from you. Pay attention to a certain U.S. House Oversight Committee field hearing taking place in Florida in about a month. Fermi paradox solution is very simple.

[@mjmeans7983]

So I see that there is a cosmic event horizon which is the largest comoving distance from which light emitted now can ever reach the observer in the future. But is there a name for a distance at which light cannot possibly make a round-trip between the two objects due to universe expansion? i.e. Two-way information travel is not possible.

[@KarelGut-rs8mq]

Wouldn't that just be half that distance?

[@Maelthras]

1/20th of a second is the limit of reaction time, maybe physically right? When I watch a timer ticking down I can see it moving.

[@NullHand]

You "see" an image processed by your brain, which has conveniently accounted for the average 300 milliseconds it takes your optic nerves and occipital lobe to update new visual field data. We hallucinate moving objects 1/3 seconds into the future to account for this. Which is why we can catch a fly ball or frisbee. This also explains many optical illusions, and those interesting "trails" we sometimes see when injesting the wrong mushroom metabolites....

[@KempPlays]

​@NullHand Another interesting effect is that when you change where you're looking rapidly it takes a moment for the sensory input start making sense again. Your brain fills in fake memory of what it thinks you would have seen in that moment. This is why sometimes when you look over at an analogue clock with a seconds hand it seems like it takes ages before it does the next tick. It ticked in that moment but you didn't catch it and then your brain extrapolated a fake memory of you looking at the clock for that moment longer but with the hand in its current position. Then you have to wait almost a full second for the next tick plus the second or so of fake memory. Once you start to learn about senses and memory you find out it's all a web of lies 😂

[@robertpendzick9250]

@@KempPlays So we only sense the past. But how long is the present not with regard to our perception? (those chemical life signals of eyesight, brain activity and nerve activity take time) Our responses are due to past events, so how long does the past last? (seems it lasts a long time(?), but how far ahead from our perception does the future actually exist?

[@Maelthras]

@@NullHand 3/10 of a second, thats bs.

[@NullHand]

@@Maelthras Do this little experiment. Next time you are stopped at a red light several cars back, count the cars. When the light turns green, start a stop watch timer (app is fine). When the car in front of you gets off the brakes, stop the timer. Betcha the number of seconds is damn close to 1/3rd the number of cars. Humans can beat the 300msec response time with intense focus and training. But the population average when just going about your day always shows up in traffic.

[@saiprem]

Question: if a photon can be captured by the gravity of a black hole thus causing it to go into orbit around it, is it possible that a photon can get a gravitational slingshot effect speeding it up to faster than the speed it approached the black hole, which was the speed of light?

[@jemhoare2105]

I think that the word "captured" and "orbit" specifically means the object isn't on a slingshot trajectory.

[@Smo1k]

Effects that would increase the kinetic energy of a photon, such as moving with the gravitational field down to, say, Earth, blueshifts the light, it doesn't change its velocity.

[@peters616]

Why can't we just :) ... use the moon as a secondary lens to a solar scope since it seems to line up almost perfectly in size with the sun when looking from the Earth, as we know from solar eclipses? Wouldn't this dramatically reduce the distance we need to position the solar scope collector? I know it isn't the classical two lens telescope configuration but can't we account for the double refraction of photons using a powerful computer?

[@vicvicious5328]

Please anyone know where to get/download these sci-fi books for free 😩

[@frasercain]

Go to your local library. Put in requests for all the books you want. Over time they just start showing up and you read them. If you don't get to the book, return it and request it again.

[@dannybell926]

Coruscant because i still dont comprehend this phenomenon

[@diegobarna]

Why do light arrives later than the gravitational waves? Shouldn't arrive at the same time?

[@frasercain]

The photons have to do a random walk through the stellar material until they reach the surface. Have you ever heard that photons generated inside the Sun take 50,000 years to reach the surface? It's like that...but quicker.

[@diegobarna]

@@frasercain Right, that makes sense. Thank you very much!

[@gpaul8062]

As per last week, how do we know betelgeuse didn't nova all ready it being 600 MLYs away?

[@gpaul8062]

Correction 600 Lys away

[@deltalima6703]

Because the only clock you have is here on earth, and according to that clock, it has not happened yet.

[@hoefty232]

What if the universe is not expanding, but there is a property of light that we don't understand, in which it's energy inherently decreases over time?

[@frasercain]

This is a theory known as "tired light", but it makes predictions that fail to be observed, while the expansion of the Universe passes the tests. Here's more info: en.wikipedia.org/wiki/Tired_light

[@masi416]

I can ignore wrong physics in movies mostly. Magic like technologies is fine for me. But the simple stuff, like falling from a building and landing flat on concret, but it's fine beacuse you are surrounded by a metal capsul/suit. A rotating space ship/sation losing energy and also its spin gravity.

[@stephenkiely9244]

Hey Fraser, is the ever a scenario where light doesnt move at the speed of light?

[@petevenuti7355]

I'm not Fraser but, anytime light isn't in a vacuum, the denser the medium it has to pass through the slower it goes..

[@jemhoare2105]

If the universe expands more quickly above than below me, do I move downwards?

[@NullHand]

From the perspective of someone in a galaxy 10 billion light years over your head... You DO. But from the perspective of someone in a galaxy on the other side of the Earth 10 billion light years below your feet.... You are doing the Superman thing straight up and hauling the whole planet with you!

[@bozo5632]

Hoth

[@emmettobrian1874]

Question, if a black hole had a binary star like Cygnus X-1, and that star collapsed in a supernova, would the black hole be pushed away by the matter traveling towards it? Or would the black hole move towards the supernova because gravity pulled on the advancing wave of matter?

[@NullHand]

It would fly away from the companion it was formerly gravitationally bound in orbit with. Just like if you and an ice skating partner you were spinning fast in circles with by holding onto two ends of a scarf. Now imagine she either lets go of her end... Or just explodes.

[@agentdarkboote]

I don't exactly agree with NullHand, the matter is still mostly concentrated in the same place so the force of gravity is still there. It is true that as more of the mass gets to a radius from the star that exceeds the orbital distance of the star from the black hole these shells of matter would no longer be contributing to the net attraction, causing the orbit to expand. But I do think the expanding cloud would push the black hole for two OTHER reasons: one, the infalling matter has momentum and this would be conserved. Two, an accretion disk would form, the cloud would push against that, and that would also pull the black hole further away.

[@dgEari]

Question: If we could se a Galaxy exiting the observable universe, what would we see? Something like the (wrong) example of a person falling in a Black hole and slowly disappear? Also, since the center of the observable univervse is pretty much where we are, can we be far apart from some other Observer that can see a bit more of whats outside our bubble, and if we communicate with this observer, would we be getting information of places casually disconnected from us? Does It brake space police laws? Say hi to Pam

[@frasercain]

That's kind of like asking what would happen if you walked to the very edge of what you can see in a fog. You'd see that spot clearly and now a cloud of fog around you.

[@jcoghill2]

The problem with gravity waves is that we have no way to interact with gravity other than to observe it. We figure that part out and the world will change real fast.

[@frasercain]

We can make gravity waves by moving mass, but they're not very strong compared to colliding black holes.

[@anthonylester2128]

Quantum entangled particles can 'communicate' with each other instantaneously across any distance. Doe that mean we could use them to communicate instantaneously across space e.g. use a quantum computer to have real time chats with Mars colonists?

[@ashnur]

This is not the best way to describe what is happening. It better to speak of correlation than communication. It might look like it's communicating, because we build a narrative of superpositions and multiverses. Collapsing the state only means communication if you don't get the point in Schrödinger's thought experiment. But then I would posit, if that's true, then platonism is also true, and the law of attraction, and every god and every idea, must exist somewhere.

[@matthewbaker6177]

The player of games....awesome book. Actually any by Iain banks are simply amazing. He is missed.

[@mytube001]

That's his best, out of his Culture novels. He's trying too hard in some, making it weird, like Use of Weapons. The Player of Games is very straight-forward and well told.

[@NullHand]

I really liked his last, the Hydrogen Sonata. Complicated plot for sure, but I like that now. He seemed to grow the concepts of his Multiverse into a place so complex and vast that even the hyperdimensional swashbuckling ship-minds are left scratching their bridges about how to proceed. And I feel for the antagonistic undecalute player. Just six strings are more than enough to see out my three score and change....

[@bradmiller3557]

If there was a single “big bang” then wouldn’t it result in a sphere shaped explosion. If so, where is it’s epicenter?

[@dustinpoissant]

Is it possible that dark energy is something that red shifts light as it passes through it without actually expanding space.

[@NullHand]

That's a really good question. And it was tossed about a lot after the initial study that showed accelerating expansion. As I recall, nobody could come up with a reddening agent (like dust) that would affect all wavelengths equally. Also there is Olber's paradox. Without space continually redshifting the light (and apparently pulling galaxies away from us at > than c) then our nice black night sky should be slowly brightening as the light from more and more stars and galaxies enter our light cone.

[@dustinpoissant]

@@NullHand assume its not expanding, that doesnt mean it is collapsing. If the universe is uniform it all matter would be pulled in all directions, aka not moving at the largest scales, just galaxies rotating and loc clusters merging

[@NullHand]

@@dustinpoissant Yes, that is what was believed at the turn of the last century. Einstein even modified his field equations to add a cosmological constant to kinda/sorta make it work. He knew that such an arangement would be unworkably unstable without an "antigravity" term. When Edwin Hubble found evidence for recession he basically said "lol, my bad, erase that cosmological constant thingy". Turns out it is back because the recession of distant objects is accelerating, not decelerating, but we re-named it Dark Energy. We still don't know if it is a Constant. Incidentally Einstein reputedly called his addition of the cosmological constant "my greatest blunder". He should have cut himself some slack. Observation killed it. And further observation brought it back.

[@ramphy1]

Mustafar!

[@charleslivingston2256]

Mandalore

[@deltalima6703]

I have a fun question for fraser. Does time run at the same rate at the center of the earth as it does in deep space, since there is no net gravitational force there? Or does time run at a slower rate than it does on the surface of the earth, since there is lots of mass around warping spacetime? Is anyone curious about this question?

[@frasercain]

Time runs at a different rate on the surface of the Earth than deep space because of the gravity. You can think of the extreme version in the movie Interstellar where a few hours turned into 30 years because they were close to a black hole.

[@deltalima6703]

@frasercain yes, obviously, but thats not the question. Question is about the center of the earth.

[@frasercain]

Ah, so you're asking if having the forces of gravity balance out at the center would make the time dilation go away? My instincts say you're still in a gravity well, even if you're not feeling a force. When you're in orbit, you're not feeling any forces, but you'll still experience time dilation based on your proximity to the gravity well.

[@deltalima6703]

@frasercain Yes, exactly. 😀👍 I suspect you are probably right. When it comes to science though, I am wrong sometimes, even about things that really seem reasonable.

[@deltalima6703]

Orbit would have that centripetal force in newtonian mechanics, whereas inside a shell has no newtonian forces. It seems like a dumb question, but the galaxy acts like a large diffuse mass, and the question matters in this context.

[@JayCross]

The great attractor is hidden by dust in the Milky Way. It is cosmically fairly nearby. Is it big enough that we should be seeing an excess of Gravitational Wave events from the objects in its galaxies? Can that tell us something new about this massive cluster?

[@frasercain]

From what I could find, BH mergers are in the 1.4 billion ly range and above. So nothing has been seen as close as the Great Attractor which is 10% of that distance - 147 million ly. en.wikipedia.org/wiki/List_of_gravitational_wave_observations

[@JayCross]

@@frasercain Though the NS-NS mergers are in the right range.

[@frasercain]

I wonder how many you'd need to generate some kind of statistical correlation.

[@JayCross]

@@frasercain I was also wondering that.

[@farmergiles1065]

Does the present really exist? I couldn't say at this time.

[@JanKanis]

I remember that the clustering of distant dwarf planets, which gave rise to the recent planet 9 hype, has been explained by observational biases that the original analysis did not take into account. So nothing to see there, there's no evidence for a planet 9 left.

[@lawrenceiverson1924]

Fisherman on the inland sea ---Ursula K LeGuin Plus everything else she wrote ,of course