For getting the feel of the milky way, I think there's nothing that is better able to simulate it than a video game, ala Elite Dangerous. I loved to navigate its galaxy map. The size of the Milky Way, the numbers of stars and distances between them are of scale in there if I recall correctly.
I recently saw a video that really put in to perspective for me just how impossibly large the Universe is. The idea is finding your way back to Earth from 1 billion light-years away. Not just thr Milky Way, but also how much more there is outside of it.
One particular "feel" that people often get wrong: on a scale of up to around 1000 light years in each dimension (on the order of a million stars, or a hundred thousand sun-like stars - I haven't done the integrals over the density), the placement of star systems is largely homogenous. Most galaxy-scale structure (such as the spiral arms, or core vs rim) only starts becoming significant when you get bigger than that.
Now there are 2 caveats to this - first, there is a measurable density difference as you get closer to the galactic plane. And second, globular clusters do do their own thing.
What this means for fiction is that you must commit to either:
* The overwhelming majority of systems must be irrelevant; relevant systems are hundreds of lightyears apart (it is trivial to disappear into uncharted systems assuming you can maintain your spacecraft), and galactic structure does matter. Or,
* If even a modest percentage of systems are to be relevant, then you can't care about galaxy-scale structure at all. And you need to have something stopping people from gratuitously flying out of bounds (this might be as simple as "no compatible languages and no compatible fuel pumps").
That's interesting, so fiction would be more realistic if they always have distances of hundreds of lightyears apart?
But that means that galaxy-scale structure actually does matter, right? A hundred thousand sun-like stars isn't all that much, I'm guessing only a small percentage-points of those would have a planet in the correct orbit for terraforming, and you'd need to go outside your proposed 1000 LY volume?
Unsurprisingly with ~400 billion star systems, less than 0.01% have been explored.
If there were galactic empires like you see in science fiction, the amount of administration required to deal with that many systems would be mind boggling, the volumes of data would be staggering.
I recently contemplated about a thing: on a galaxy scale, the speed of gravity (or gravity change) should have a somewhat noticeable effect. There's a slight pull towards a star on the other side which is not there anymore for 50000 years! Of course there's some other star in that place, but I wonder how minuscule that effect is. Would it speed up or slow down rotation of outer regions of galaxy?
Gravity works the same as light - if you see it somewhere, it pulls you in that direction. The fact that it’s somewhere else now is irrelevant, because the now is tightly coupled to the where thanks to relativity.
I am not familiar, so I don't know, but do they assume something like 31,536,000x speed of light to make the galaxy even remotely navigable, e.g., the ability to navigate from Earth to Alpha Centauri within 4.34 seconds?
There's FTL travel of course, but you can navigate at 'normal' speeds as well. The normal speeds really show how there's no way to get to any other object even at full throttle (without FTL). It's just for asteroid belts, space stations and so on. the way they did it gives a really nice intuition of the enormous size of space. It's a fantastic game!
This was already present in Frontier: Elite II released in 1993. You could travel at sub-light speeds as far as you wanted, visiting gas giants within the same star system and scooping fuel. But to get anywhere else, hyperspace was the only practical option.
The crazy part is that this 3D game was programmed in 68k assembly, ran smoothly on Amiga and Atari ST home computers, and fit on a single 1.44MB floppy. The massive universe with realistic solar systems was almost entirely procedural.
Jupiter is between 4 and 6 AU from Earth. So at the speed of light it would still take over half an hour to get there. It’d be a dull game flying anywhere at sub-light speeds.
It’s been over thirty years since I played Frontier, but I think you could accelerate the in-game time. So you didn’t have to sit still for hours to get to Jupiter. For your character, that time did pass.
Agree. I've mentioned to a few friends how that feeling of emptiness and scale is quite awe inspiring and was a first for me. Theory can't replicate how small and isolated you physically feel when you are between systems. At least not for me.
You certainly could simulate time dilation, I'd be surprised if that isn't already an element of some game out there.
If you go close enough to the speed of light, what you actually see is that space appears to shrink (in the direction of travel) and the trip seems to take less time than light would, because you've apparently covered less distance. Of course what those on the planets would see is that time has been moving oh so slowly on your otherwise speedy ship. There are equations you incorporate into a simulation that would account for this. If the game mechanics were such that you could could see what day/month/year it is in local time, vs your ships time, it would quickly become apparent that bashing through the void is no way to get anywhere.
Sure you could. Each local area (such as a planet) is a single timezone, and everyone there experiences time at the same rate. Someone leaving that timezone would experience time dilation... But in game it would just appear as a communications lag, just as it is for people on different planets. Then, once you've arrived at your destination, there's no longer any lag with your new timezone, and your lag with the original time zone is now fully synched with everyone else on your new planet.
Player A remains on planet A. Player B remains on planet B. Player C commutes between planets A and B, accelerating hard enough for measurable time dilation.
When I try to explain to someone just how big and massive our universe is I usually fall back to the Voyager 1 satellite which was launched almost 50 years ago. I like to tell people that it is traveling at an amazing 17km per second! Even at such an amazing speed it has still only just traveled approx 1 light day. At such a speed it will travel about 1 light year every 18,000 years.
Then I like to say the nearest next start is roughly 4 light years away. So even at 17km per second, or about 10.5 miles per second, it will still take approx 72,000 years for it to reach the nearest star.
That star is 4 light years away and our galaxy is about 100,000 light years across. The next galaxy is about 2.5 million light years away!!! So at the incredible speeds of one of our fastest man made objects it would take something like 45 billion years to just get to the next galaxy!
Seeing how the known universe is estimated at over 46 billion light years in size and looking back on the other numbers I wrote it quickly becomes apparent that to travel across the galaxies one would need to be able to reach unbelievably unimaginable speeds. Even the speed of light as you mention would not be even close to fast enough to get anywhere significant.
On a side tangent I was always a trekie back in the day. I know their warp drive was faster then light but now I almost want to go back and look at the math of how fast they must have been going to be going the distances they were going.
That is assuming the objects will be at the same place relative to us, which is not true. Like reaching Andromeda. Voyager I will reach oyr neighbouring galaxy in roughly 4.5 billion years, not 45, that's because Androneda is moving in our direction. Reaching Proxima Centaury would take longer than your estimation because of it's orbit around Alpha Centauri A/B.
Estimating time-to-arrival when your destination is also moving at ludicrous speeds is incredibly difficult.
> I almost want to go back and look at the math of how fast they must have been going
While there's a rough polynomial (v =~ c * w^3, I think) for post-TOS Star Trek warp factors, the only consistent rule: a starship travels at a velocity that helps tell a good story.
It's fun to try mapping Star Trek stories, anyway; it helps you ponder how much time they must have spent in transit. They have to find things to occupy their time.
Yes I think you are spot on, they move at the speed of how fast the plot needs them to move. After posting my comment and looking online at some suggested speeds for the various warps speeds it is very inconsistent and far from realistic given the size of the universe. One would need to be able to travel at something like 100,000 times the speed of light to realistically travel just around our galaxy. Probably would need to travel at about 1,000,000 times the speed of light wanting to make it to the next galaxy in a realistic time. Even at 1,000,000 times the speed of light it is going to take years to just reach the next galaxy so it is no where near fast enough to get around like they did in star trek.
But I absolutely loved the show growing up so not here to knock them. I am sure in hindsight they may have come up with a better definition of how warp speed works and how they can travel great distances. I won't think about it too much.
It’s not that light speed is too slow, it’s that our lives are too short. If you can solve mortality, you just hop on board your 17km/s ship, turn YouTube on (all of it), and spend a relaxing 72,000 years getting to Alpha Centauri.
If you accelerate at 1g half way there, then decelerate equally fast for the second half, you can reach almost any point in the galaxy in a single human lifespan - thanks to time dilation.
I'm not sure if the CMB itself will decay fast enough with the expansion of the universe to avoid 1g eventually getting you hull eroded by positron-electron pair production from photons blueshifted above 1022 keV, but that's in the set of things you need to think about.
I found a neat little artist page where they have the local star map, the milky way, the local super cluster and a bunch of other neat laser crystal stuff: https://www.bathsheba.com/crystal/#astro
I'd get one, or for that shipping cost make a better one and send them the data, but current shipping in and out of the US is ... interesting.
A quick google on openscad shows how someone build a model of the solar system: https://www.chrisfinke.com/2016/03/08/animating-the-solar-sy... if anyone else wants to have a go this would be a good place to start generating a model to send to the artist.
When the Fermi Paradox was first posited, scientists and engineers seemed to believe that interstellar travel was soon to be technologically achievable, a few decades, maybe centuries for the less optimistic. Progress around space propulsion has kind of stalled since then and we should maybe question the possibility of interstellar travel as this would give an easy but unpleasant answer to the famous paradox.
Right- “where are all the aliens?” is answered by either “they don’t exist” or “they do but physics of the universe prevent them from moving between solar systems.”
Or: we're the first (or among the first). The history that led to space travel (modern human technology) has passed through an insane amount of unlikely scenarios.
A few of these:
* Astronomical: the sun is unusually calm for a star. Jupiter blocks comets. Saturn blocked Jupiter from destroying the Earth.
* Earth is 4.5 billion years old. In the next 0.5-1 billion years Earth will become unhabitable because the sun's luminosity is increasing. We're in the twilight years of the (life-supporting) planet.
* Above point + think about all the species that came before us. Life appeared 3.5-3.8 billion years ago. It took that long to get to humans.
* Dinosaurs got wiped out. Would humans have even evolved if a cosmic event hadn't cleared the board?
* We think that human ancestors dropped down to about 1000-100,000 individuals about 900k years ago.
There's also the question of how many sun-like stars in terms of metallicity there are that preceded the sun. Our sun inherited a lot of heavier elements from a previous generation of star(s).
Add all of these together and we might be early to the party.
I believe this argument is fallacious. There could be infinite other ways a species could have evolved to acquire space technology. A smart dinosaur that evolved to use arms and tail could perhaps have built an industrial civilization. They would’ve been now 100 million years old! Imagine the progress. Them being wiped out probably just delayed civilization by millions of years.
Well, dinosaurs learned to fly instead. And perhaps they ended in a local maximum that made them survive and thrive but did not allow development of larger brains.
Not that humans with their troublesome egos are necessarily anywhere near global maximum.
I can’t vouch for its scientific plausibility, but one of my favorite bullets to add to this list comes from Frank Robinson’s novel-length scifi exploration of the plausibility of extraterrestrial life:
“The next step is crucial. The simple organic molecules have to be shielded from the ultraviolet radiation of the primary. That requires a large body of water—an ocean—to protect them. No protection and the molecules break up as soon as they're formed. And oceans of water are … extremely rare.”
…
“But something else is rarer still. The next step in the creation of life is when the amino acids form into long chains.
Left in the ocean, they drift apart as easily as they join together. There has to be a means of concentrating them. Once a certain level of concentration is reached, they'll form long chains, more complex molecules, automatically. Heating isolated bodies of water would help, say tidal pools warmed by hot lava and occasionally replenished by the sea.”
…
“Do you understand, Sparrow? Tidal pools implies tides and that means a moon large enough to raise them—though not too frequently, because you might dilute the pool too much. A combination of the primary and the moon would raise larger tides less often, and that would be a happy medium. What's required, then, is a planet that has land surfaces, oceans, and a large enough satellite to raise suitable tides. The action would concentrate the simple amino acids and they could combine into the longer chains.”
The novel is The Dark Beyond the Stars, and I recommend it highly.
I first read that same argument when I was twelve or so way back in the day in The Tragedy of the Moon (1973), a collection of nonfiction science essays by Isaac Asimov.
Or by "none exist right now nearby". If there are technological aliens 3 bly away and 3 bya, we won't likely discover their signals. If there are technological aliens 10 ly and 10 ya then we're extremely likely to pick up their signals (if they emit any), but they're not likely to come here -- not anymore than we are to go there. The Fermi paradox is most easily understood as "the probability of two concurrent technological species in different but nearby star systems is vanishingly small".
For all we know there have been thousands of technological species in our galaxy, but never two at roughly the same time and roughly close together, and never will be.
I dislike either/or answers in such open-ended scenarios. It points to our lack of humility in the vast unknown.
eg: maybe they exist(ed) but once a civilization gets advanced enough to build FTL-like travel, they invent AI and use it for warfare and then soon cease to exist. This would mean there are potentially many civilizations (and AI?) that are budding and could travel through the universe.
eg: We aren't in an interesting enough place to bother visiting.
eg: they exist and know about us but have "prime directive" (Ala: Star Trek) laws that state they can't make contact until we reach a stable enough civilization to invent warp drive (or some other advancement.)
eg: There is some exotic reason that our pocket of the Milky Way is un-navigable.
We know enough physics to rule out any ftl travel. Assuming that is correct which seems very likely they can't get here, even radio signals is question able - even if radio signals can get here either they have already passed and their civialization (sun) is dead or ours will be dead by the time they arrive.
Cherenkov radiation is a proof, that FTL is possible. We just cannot accelerate enough. However, «burps» from blackholes are proof that blackholes can do that. To achieve singularity, outer layer of blackhole core must spin at a FTL speed anyway.
Cherenkov radiation shows that FTL is possible in a medium where light is slowed down below a the maximum possible speed allowed by special relativity. It does not show that FTL as usually understood is possible.
This feels very defeatist to me. Technology continues to advance, exponentially. And there are hypothetical ultra fast space travel technologies that we haven’t yet been able to fabricate but could theoretically in the future. e.g. Alcubierre warp drive.
Why should we believe it will continue to advance exponentially? And even if it does, we many find none of the hypotheticals pans out - perhaps we advance exponentially and there is nothing feasible to reach even 0.01c
Yeah it's always quite naïve to say technology will be always exponential. We only had like a few thousand years - if it's logarithmic we wouldn't know it for the next 10000 years.
Especially if we are actually on the cusp of ASI from self-improving AGI systems. That seems like the most likely scenario where technology emerges that we cannot currently fathom.
The fabric of spacetime itself sets the ultimate speed limit. Nothing can locally move through it faster than light. For example, gravitational waves ripple across the universe at light speed.
Anything that exists within spacetime is bound by this rule. The only odd exception people point to is quantum entanglement, but while the correlations appear instantaneous, they can’t be used to send information faster than light. Sending matter is distant second.
So, if we ever hope to travel faster than light, we wouldn’t do it by "outrunning" gravity. Instead, we’d need to find a way to manipulate spacetime itself, like bending, warping, or reshaping it ... since that, in the first place itself, is what is defining the limits of motion.
I think our recent forays to microscopic and sub-microscopic things like computers have really distorted our views. Just look at something like EV. Give say 10x efficiency(very high) increase and we are actually still faraway from even interplanetary travel.
Physical world is big and getting from one point to other takes lot of energy and involves lot of mass.
More like technology evolves in spurts. Huge gains within a specific area for 2-3 decades and then only small incremental advancements for the next 2-3 decades.
If the Alcubierre drive were possible, some civilization would have already discovered it, and we would see evidence of its use. This is certain to be the case with any kind of FTL travel, if such a thing is even possible.
But when we observe the universe we see nothing. Therefore either no advanced life exists in the universe besides ourselves, which seems unlikely, or none have spread to space in any significant degree and FTL is either impossible or so difficult no one bothers. There doesn't seem to be a secret third thing that both satisfies our observations and obeys known physics.
We do know how to build interstellar-capable propulsion. It'd still be a generational ship but we know how we could do it within the span of a few human lifetimes. Building them is a matter of organizing the resources to actually make it happen, and we haven't had the collective will for anything like that yet.
We do not know how to build one. We could build something of that size maybe, but we couldn't make it last long enough to get anywhere. Some astroroid will randomly hit it in the worst spot and break it.
It'd have to be pretty darned big, to sustain a population large enough to remain viable for a couple of centuries. You'd then have to figure out how to get enough delta-v on it to escape the solar system, but then you'd also need a way to get yet more delta-v at the other end, to slow enough to get captured in a useful orbit, or else fly right on out the other side. Assuming there's a planet you're aiming for, you'd want to establish an orbit of that. So this has to be a small asteroid scale ship, with propulsion that works, after centuries of micro meteorites and radiation, and possibly substandard maintenance.
I’d be pretty pissed at my parents if I was born on a Starship and condemned to die on it too. Imagine living your entire life in a Winnebago and you can’t even go outside.
... which begs the question of who would really arrive at the destination. Our own civilization starts to rebel at things that were heralded by the previous generation because the current generation doesn't remember the problems that were solved. In two generations, the humans that remain might not leave the ship at all despite having a whole planet (or multiple) to inhabit.
I doubt that number would be sufficient. Such ship would have to be very stable society. So getting enough people to harshness of unsettled planet is very tall ask.
I believe historically it was either for profit, which there is unlikely to be much in medium term. Or because the new place was expected to be better. Mostly due to resource constraints. But generation ship should be quite optimal. And well outside magic level tech there is not much to do on empty planet.
I follow what you're saying, but many folks on this planet have far less opportunities than such a trip might provide. Guaranteed food, housing, access to cutting edge healthcare, a likely united community. I'm assuming these ships would be fairly big. It would definitely be different but-- would it be as bad as we think?
Unfortunately, I suspect that any starship that could bring with it all of those services would also bring with it the economic and political strife of Earth. The are lots of examples of democratic states turning into oligarchies or worse in recent history so that can't work in it's current form at least.
The closest analogue in the real world to the ideal that you describe is, I think, Cuba. It does guarantee food and housing, and it does have a remarkably advanced healthcare system plus what is reportedly a united community. Perhaps most interesting of all, it's politically isolated like a starship would have to be by its nature. Even then, one would have to be either pretty brave or desperate to go along on the journey, as modern Cuba has only been around for half a century and that's at the absolute minimum of an intergalactic starship's practical mission duration.
It would be better than living your entire life in a literal cage on earth. But I think it would be worse than even being a slave on earth. A slave can touch grass and hope to run away. A person born on a generational ship would be effectively enslaved (to perform necessary ship duties). You mention 'cutting edge healthcare', but on earth that requires the substantial and diverse resources of an industrial civilization. The research of millions of people and the infrastructure to breed nuclides and manufacture precise machinery. Does this generational ship have a modern chip fab on it!?
Well, it continued to bother Newton. Here, he seems to be foreshadowing the concept of fields:
"It is inconceivable that inanimate Matter should, without the Mediation of something else, which is not material, operate upon, and affect other matter without mutual Contact... That Gravity should be innate, inherent and essential to Matter, so that one body may act upon another at a distance thro’ a Vacuum, without the Mediation of any thing else, by and through which their Action and Force may be conveyed from one to another, is to me so great an Absurdity that I believe no Man who has in philosophical Matters a competent Faculty of thinking can ever fall into it. Gravity must be caused by an Agent acting constantly according to certain laws; but whether this Agent be material or immaterial, I have left to the Consideration of my readers."
Yep. From a light emitter's perpective, it is directly embedded in all of the places surrounding it that its light would eventually reach. Your eyeball, a distant dust spec 4 million light years away, and a black hole are all directly adjacent and it tosses photons onto the shell around itself, painting it with light. The photons arrive at the same instant that they are emitted, if you don't count the millions or billions of years in between. And the photons don't.
It’s interesting that from the star’s perspective the light is immediately hitting the objects, yes those objects might have 200 million years of random chance and (possibly) free will determining their positions when the light hits
I'm not a physicist, but I believe that's the exact insight that led to special relativity. It goes something like: If your moving at 1,000kmh next to a jet moving at 1,100kmh then the jet is moving at 100kmh relative to you. Eventually people realized those wasn't the case with light. No matter how fast the observer is, light still moves at 299,792,458m/s. Einstein figured out that if the speed of light is fixed despite relative motion, then time must slow down as you move faster. So from the perspective of a photon no time has passed since its departure.
Time does not pass for photons. So yes, that is exactly what GP is saying.
There's also a different thing that GP might be hinting at, which is that by convention we assume that the speed of light is the same in all directions, but there are other conventions we can use as long as the round-trip speed of light agrees with that which we've measured (and yes, we can only ever measure the round-trip speed of light, FYI). Another convention is that all the light we see takes zero time to get to us but the light we emit goes out at half the speed one would expect with the standard convention (known as the Einstein synchronization convention). So instead of "light we see from Alpha Centauri is 4 years old" or "we see Alpha Centauri as it was 4 years ago" we can say that we see it as it is right now, but this is not a very commonly used convention.
Yep, this is what he saying, but this is not what photon does. Photon must perform different amount of wave cycles to reach 1 meter or 1 trillion metters. These cycles can be counted.
In a lab setting, yes, but across such distances, no. Photons don't have a cycle counter on them, so they don't keep a cycle count and can't reveal that cycle count. All we can do is measure frequency/wavelength (spectrum, really, since we're going to see lots of photons, not really onesie/twosies) and intensity, and we can use the astrophysical distance ladder to figure out roughly where the emitter must have been.
Except that's not from the frame of reference of the photon. At the speed of light, the Lorentz transform shows that 1) Time stops completely, 2) All distances in the direction of travel collapse to zero. So in a very real sense, "from the photons perspective" it never exists and the point it is emitted from and the point it is absorbed at, are the same point.
Experiencing time and having mass are linked in a very deep way. Objects that experience time, i.e. have some kind of state evolution, must have mass, this is how we know the neutrino has mass even though it's smaller than we can measure, because we measure them oscillating between the various flavours of nutrinos.
This is also how the Higgs mechanism gives rise to "rest mass" in most particles, by constantly exchanging weak hypercharge with them. This oscillation back and forth gives them mass.
That thought randomly hits me all the time when I'm taking out the trash or whatever and just happen to look up. That and the fact that the Bootes Void and Phoenix A* exist out there.
Nit of a nit; the energy might take that long, but the photons that reach us on Earth are not directly created by the nuclear fusion reactions in the sun's core. Fusion creates high-velocity nucliei and other particles, but not visible light. The resulting heat creates photons which are rapidly destroyed by absorption. Only photon emission from the outer most layers of the sun reach Earth.
I.e., that bit they refer to as the photosphere, effectively the radiating 'surface' of the sun, is the source of the solar photons that strike us here. That trip takes about 8 minutes.
The photons were created a long time ago in the core. It takes thousand of years for it to reach the surface, and THEN it takes 8 minutes to get to us.
The photons created in the core are some seriously energetic gama rays. Sure, gama rays are very penetrating, but the solar core is dense, and it's about half a million miles to the surface, so these mostly get absorbed right there in the core, making stupendous amounts of heat. At any given depth that means that matter is going to re-emit photons, but never any more energetic than the original ones that are absorbed, but that radiation will be reabsorbed as well. That process of emission and reabsorption means that energy travels to the surface a lot slower than light in a vacuum, and sure, it takes a long time for that energy to reach the surface, but the photons that reach the earth are only the ones created close enough to the 'surface' to escape into space.
Photons are not created on the surface but in the core where the environment has the higher pressure needed for the physical creation of the photon and the photon takes about that long to work its way out.
Is this in any sense hydrogen being converted to photons? Photons are massless, but… the mass of the elements in the star are converted to pure energy?
What is the ratio between those and well heat due to nuclear reactions and well pressure. Hot stuff generates visible photons. Say like incandescent light bulb.
So there must be a range in age. As some closer to still hot surface don't need to travel through parts of the sun.
This is interesting to me because somehow I’ve had in my head that if we develop the ability in the next couple centuries to send probes interstellar it would be a longer list of possible targets. What this makes me realize is the list of places we visit even in the next thousands of years - even with incredible leaps in propulsion - is very finite. Space may be really really big but the part physically accessible even in long timescales is limited.
During COVID, I had a lot of spare time and an aversion to reading the news or indeed anything on social media. So, I got interested in trying to wrap my head around the scale of the universe. I built an app called VOS - https://vos.ajmoon.com - which would plot things at scale on a map, allowing me to plan a walk (e.g. from the sun to Pluto) with various celestial objects at that scale. Then I made videos of some of those walk plans, explaining what you'd encounter. It was a lot of fun!
I always wondered why do we care about stuff outside of Solar system. Apart from the "wow" factor, what else are the real uses for info? I think anything beyond solar system is unlikely to have an impact on the life on the Earth.
A Type II supernova within 26 light-years of Earth is estimated to destroy more than half of the Earth's ozone layer. Some have argued that supernovas within 250-100 light-years can have a significant impact on Earth's environment, increase cancer rates, and kill a lot of plankton. They can potentially cause ice ages and extinctions. Within 25 light-years, we are within a supernova's "kill range." Fortunately, nothing should go supernova close to us for a long time.
That's the practical reason for why one might care. Keep in mind that the solar system is rotating around the galaxy, so over time different stars become closer or farther away.
As the Kurzesagt video points out, a supernova within 100 light-years would make space travel very difficult for humans and machines due to the immense amount of radiation for many years.
Still, I think the primary value is in expanding our understanding of science and the nature of the universe and our location within it.
Very distant systems, i.e. extra-gallactic, like quasars, are used for the most accurate coordinate systems (e.g. the International Celestial Reference System/Frame, ICRS/ICRF3, the Gaia Celestial Reference Frame, Gaia–CRF3), because their angular velocities are negligible due to the huge distances where they are located.
Basing an inertial coordinate system on the observed positions of the bodies belonging to the Solar System is affected by much greater errors caused by the imperfect modeling of their relatively fast movements.
Using stars that are outside the Solar System is much better, but using distant extra-gallactic objects is even better.
If we did not have the "fixed" stars as a background on which to view the movements of the Sun, Moon and planets, who knows how many centuries later physics and technology would have reached the current level, because when seeing only the relative motions of the planets, without a fixed reference system, those are much harder to understand.
For interplanetary navigation, receiving signals from pulsars can be used as a backup or a replacement for atomic clocks. Individual pulsars, especially when young, are sometimes affected by "glitches" when their moment of inertia, thus the frequency of their signal, changes, but if multiple old pulsars are monitored, any glitches should be detectable and they should not affect operation.
Even the primitive humans of many thousands or tens of thousands of years ago knew to predict seasons by observing the rising stars and to navigate with the help of star gazing.
For the ancient civilizations dependent on agriculture, observing the stars, e.g. to determine when to sow various cultivated plants, could have a life and death impact, not a minor influence upon their life.
Comparing other stars and planets tells us how unusual (or not) Earth is. That perspective matters for understanding climate, habitability, and even life itself.
Most of the imaging and signal-processing tech built for astrophysics ends up in medicine, satellites, and everyday devices. The "wow" factor funds a lot of spinoffs.
Space weather doesn’t stop at the edge of the Solar System. Supernovae, stellar motions, even rogue objects can affect us. Better to understand them early.
It’s long-term thinking. Nobody builds interstellar ships tomorrow, but mapping the neighborhood now is how future generations avoid starting from zero.
Honestly, it also grounds us. Realizing Earth is one small rock among billions changes how seriously we treat our only habitable home.
It should be a goal for Earth to send a probe to one of those stars. As the probe will be unmaned, a mission taking a hundred years or more is not out of question.
There are already plans to reach alpha centauri in about 20 years with unmanned probes (1). There still remain some technical hurdles in terms of the laser design to propel these probes afaik but it seems like this could be solved with more funding.
Too bad we are in the current era of eschewing scientific research in favor of crony politics.
Something like Starshot seems like it could benefit from future developments without holding back a launch today. Something with a sail can always have a laser aimed at it; maybe we launch it today with a tiny laser we fire from orbit, and in 50 years, we accelerate them to a significantly better cruising speed by firing from a laser array on the moon.
One issue with the latter is that tech is likely to advance fast enough that a subsequent probe launched a couple of decades later would overtake the first probe.
I’d still settle for getting the probes out the door because no matter what advancement happens if you can’t get them into space it’s a moot point. I’d simply take something we can reasonably launch into space for research at this point.
Also, I would love to see a lunar base happen in my lifetime
Yeah, I don’t think it will happen that fast. There are a lot of hard problems to solve, and you have to make a case for the expected scientific (or other) benefits to be worth the costs. Look at how long the JWST took from initial planning to launch, that was about twenty years, despite clear and specific objectives.
Unlikely, but possible (if the probe was really big or really chatty in parts of the spectrum we pay attention to). Tiny probes could pass by us without us noticing them I'd think, though if they needed to send transmissions back toward their origin we might pick that up.
As someone who has been fascinated by the universe and galaxies from a young age, I too thought interstellar was the way to go. Nowadays, however, I've started to feel that we've been wrongly conditioned by science fiction to see interstellar exploration as the next logical step for humanity.
Our species is still very immature ethically, socially, and politically. We haven't even learned to accept each other and co-exist happily on Earth. Our distant hominin ancestors crossed entire continents but today we set up physical borders and cultural barriers to prevent even neighborly visits. We certainly won't become the broad-minded united ethical species that Star Trek TOS/TNG portrayed within the next 2-3 centuries.
Gradual spatial expansion, and through that, gradual cognitive and worldview expansion, has been our track record. Whenever things got hairy for someone in our hominin tree at any time, they moved just a little bit more to survive.
So, I feel exploring and settling other solar system bodies should be our next logical step. There are 4 solid planets, 5 dwarf planets, and as per Gemini, ~40 moons, ~3000 asteroid belt objects, and 200000+ Kuiper belt objects, all above 10 km radius. That's a lot of nearby space to explore and more practical than interstellar. Some of them will become the solutions or refuges from our current social and political problems on Earth.
It'll take us 1000s of years more, maybe even 100s of 1000s, to do all this. Including a lot of violence, conflicts and injustice. But eventually, we will learn to develop the cooperative institutions and cognitive/ethical frameworks we currently lack to become a multi-planet species. Interplanetary cooperative institutions and technologies will emerge eventually, just like today we have airplanes, the Internet, UN, WHO, EU - institutions and technologies that, while far from perfect, seemed downright unlikely for 100s of 1000s of years of our hominin history.
some combination of nuclear radiation and/or solar seems like it would fit the bill? 100 years is within the useful range of a large radioisotope generator.
Solar would not work when you're out past Uranus or so, and the Sun is just a bright star with barely a visible disk. There's simply not enough sunlight out there, and you won't get enough light from your destination(s) star until you're similarly close to it.
RTGs lose power rapidly as the isotopes decay, and any sort of communication over those distances requires massive power. The Voyagers are essentially dead due to this issue, and they haven’t been out there nearly that long.
It would likely need a standalone fission reactor that only ‘goes hot’ when it arrives.
I’m not sure that we have the engineering ability to actually do that with any real chance of success after a 100 year deep space flight, or the willingness to wait that long to find out.
There are attempts, but they all suck IMHO :( Someday I'll get around to doing this in Three.js for real, if no one beats me to it. It's shocking that we have a million 3D sites to visualize LEO satellites and plenty to visualize the solar system, but our stellar (much less galactic!) neighborhood is all super outdated stuff only.
I guess the sad reality is that these tools aren't that useful for anything but diagramming the odd interstellar rock.
https://youtu.be/uUuM8NdmaAU?si=7It672waw734e9nK
Now there are 2 caveats to this - first, there is a measurable density difference as you get closer to the galactic plane. And second, globular clusters do do their own thing.
What this means for fiction is that you must commit to either:
* The overwhelming majority of systems must be irrelevant; relevant systems are hundreds of lightyears apart (it is trivial to disappear into uncharted systems assuming you can maintain your spacecraft), and galactic structure does matter. Or,
* If even a modest percentage of systems are to be relevant, then you can't care about galaxy-scale structure at all. And you need to have something stopping people from gratuitously flying out of bounds (this might be as simple as "no compatible languages and no compatible fuel pumps").
But that means that galaxy-scale structure actually does matter, right? A hundred thousand sun-like stars isn't all that much, I'm guessing only a small percentage-points of those would have a planet in the correct orbit for terraforming, and you'd need to go outside your proposed 1000 LY volume?
If there were galactic empires like you see in science fiction, the amount of administration required to deal with that many systems would be mind boggling, the volumes of data would be staggering.
The crazy part is that this 3D game was programmed in 68k assembly, ran smoothly on Amiga and Atari ST home computers, and fit on a single 1.44MB floppy. The massive universe with realistic solar systems was almost entirely procedural.
If you go close enough to the speed of light, what you actually see is that space appears to shrink (in the direction of travel) and the trip seems to take less time than light would, because you've apparently covered less distance. Of course what those on the planets would see is that time has been moving oh so slowly on your otherwise speedy ship. There are equations you incorporate into a simulation that would account for this. If the game mechanics were such that you could could see what day/month/year it is in local time, vs your ships time, it would quickly become apparent that bashing through the void is no way to get anywhere.
Then I like to say the nearest next start is roughly 4 light years away. So even at 17km per second, or about 10.5 miles per second, it will still take approx 72,000 years for it to reach the nearest star.
That star is 4 light years away and our galaxy is about 100,000 light years across. The next galaxy is about 2.5 million light years away!!! So at the incredible speeds of one of our fastest man made objects it would take something like 45 billion years to just get to the next galaxy!
Seeing how the known universe is estimated at over 46 billion light years in size and looking back on the other numbers I wrote it quickly becomes apparent that to travel across the galaxies one would need to be able to reach unbelievably unimaginable speeds. Even the speed of light as you mention would not be even close to fast enough to get anywhere significant.
On a side tangent I was always a trekie back in the day. I know their warp drive was faster then light but now I almost want to go back and look at the math of how fast they must have been going to be going the distances they were going.
Estimating time-to-arrival when your destination is also moving at ludicrous speeds is incredibly difficult.
While there's a rough polynomial (v =~ c * w^3, I think) for post-TOS Star Trek warp factors, the only consistent rule: a starship travels at a velocity that helps tell a good story.
It's fun to try mapping Star Trek stories, anyway; it helps you ponder how much time they must have spent in transit. They have to find things to occupy their time.
But I absolutely loved the show growing up so not here to knock them. I am sure in hindsight they may have come up with a better definition of how warp speed works and how they can travel great distances. I won't think about it too much.
I have never seen anyone writing about us having solid reference points to travel that far in case we can reach those speeds.
If you miss you end up in some empty space you won’t be able to mine anything for fuel to have more shots.
I'm not sure if the CMB itself will decay fast enough with the expansion of the universe to avoid 1g eventually getting you hull eroded by positron-electron pair production from photons blueshifted above 1022 keV, but that's in the set of things you need to think about.
This just shows a juvenile and naive level of thinking. You can't spend 72,000 years with our current brains in full conscience without going insane.
https://en.wikipedia.org/wiki/I_Hope_I_Shall_Arrive_Soon
I'd get one, or for that shipping cost make a better one and send them the data, but current shipping in and out of the US is ... interesting.
A quick google on openscad shows how someone build a model of the solar system: https://www.chrisfinke.com/2016/03/08/animating-the-solar-sy... if anyone else wants to have a go this would be a good place to start generating a model to send to the artist.
A few of these:
* Astronomical: the sun is unusually calm for a star. Jupiter blocks comets. Saturn blocked Jupiter from destroying the Earth.
* Earth is 4.5 billion years old. In the next 0.5-1 billion years Earth will become unhabitable because the sun's luminosity is increasing. We're in the twilight years of the (life-supporting) planet.
* Above point + think about all the species that came before us. Life appeared 3.5-3.8 billion years ago. It took that long to get to humans.
* Dinosaurs got wiped out. Would humans have even evolved if a cosmic event hadn't cleared the board?
* We think that human ancestors dropped down to about 1000-100,000 individuals about 900k years ago.
There's also the question of how many sun-like stars in terms of metallicity there are that preceded the sun. Our sun inherited a lot of heavier elements from a previous generation of star(s).
Add all of these together and we might be early to the party.
Not that humans with their troublesome egos are necessarily anywhere near global maximum.
“The next step is crucial. The simple organic molecules have to be shielded from the ultraviolet radiation of the primary. That requires a large body of water—an ocean—to protect them. No protection and the molecules break up as soon as they're formed. And oceans of water are … extremely rare.”
…
“But something else is rarer still. The next step in the creation of life is when the amino acids form into long chains.
Left in the ocean, they drift apart as easily as they join together. There has to be a means of concentrating them. Once a certain level of concentration is reached, they'll form long chains, more complex molecules, automatically. Heating isolated bodies of water would help, say tidal pools warmed by hot lava and occasionally replenished by the sea.”
…
“Do you understand, Sparrow? Tidal pools implies tides and that means a moon large enough to raise them—though not too frequently, because you might dilute the pool too much. A combination of the primary and the moon would raise larger tides less often, and that would be a happy medium. What's required, then, is a planet that has land surfaces, oceans, and a large enough satellite to raise suitable tides. The action would concentrate the simple amino acids and they could combine into the longer chains.”
The novel is The Dark Beyond the Stars, and I recommend it highly.
For all we know there have been thousands of technological species in our galaxy, but never two at roughly the same time and roughly close together, and never will be.
eg: maybe they exist(ed) but once a civilization gets advanced enough to build FTL-like travel, they invent AI and use it for warfare and then soon cease to exist. This would mean there are potentially many civilizations (and AI?) that are budding and could travel through the universe.
eg: We aren't in an interesting enough place to bother visiting.
eg: they exist and know about us but have "prime directive" (Ala: Star Trek) laws that state they can't make contact until we reach a stable enough civilization to invent warp drive (or some other advancement.)
eg: There is some exotic reason that our pocket of the Milky Way is un-navigable.
Why should we believe it will continue to advance exponentially? And even if it does, we many find none of the hypotheticals pans out - perhaps we advance exponentially and there is nothing feasible to reach even 0.01c
(Big IF there, I know)
Anything that exists within spacetime is bound by this rule. The only odd exception people point to is quantum entanglement, but while the correlations appear instantaneous, they can’t be used to send information faster than light. Sending matter is distant second.
So, if we ever hope to travel faster than light, we wouldn’t do it by "outrunning" gravity. Instead, we’d need to find a way to manipulate spacetime itself, like bending, warping, or reshaping it ... since that, in the first place itself, is what is defining the limits of motion.
Physical world is big and getting from one point to other takes lot of energy and involves lot of mass.
Fixed that for you. Rev up those stealth fighters!
Currently focusing on imaginary money crypto schemes and ML chatbots whose data centers use as much power as entire US states, sorry.
But when we observe the universe we see nothing. Therefore either no advanced life exists in the universe besides ourselves, which seems unlikely, or none have spread to space in any significant degree and FTL is either impossible or so difficult no one bothers. There doesn't seem to be a secret third thing that both satisfies our observations and obeys known physics.
I believe historically it was either for profit, which there is unlikely to be much in medium term. Or because the new place was expected to be better. Mostly due to resource constraints. But generation ship should be quite optimal. And well outside magic level tech there is not much to do on empty planet.
The closest analogue in the real world to the ideal that you describe is, I think, Cuba. It does guarantee food and housing, and it does have a remarkably advanced healthcare system plus what is reportedly a united community. Perhaps most interesting of all, it's politically isolated like a starship would have to be by its nature. Even then, one would have to be either pretty brave or desperate to go along on the journey, as modern Cuba has only been around for half a century and that's at the absolute minimum of an intergalactic starship's practical mission duration.
Without electricity, how well would we understand it? Just that some mysterious rocks that stick?
Wonder if one day in the distant future we’ll discover a new force we never imagined.
"It is inconceivable that inanimate Matter should, without the Mediation of something else, which is not material, operate upon, and affect other matter without mutual Contact... That Gravity should be innate, inherent and essential to Matter, so that one body may act upon another at a distance thro’ a Vacuum, without the Mediation of any thing else, by and through which their Action and Force may be conveyed from one to another, is to me so great an Absurdity that I believe no Man who has in philosophical Matters a competent Faculty of thinking can ever fall into it. Gravity must be caused by an Agent acting constantly according to certain laws; but whether this Agent be material or immaterial, I have left to the Consideration of my readers."
https://plato.stanford.edu/archives/win2008/entries/qm-actio...
For example, when we look at the sun, that’s 8-minutes-old light. When we look at Polaris (the North Star), that light is 447 years old.
When we look at Andromeda?
Yeah, that light is 2.5 million years old.
There's also a different thing that GP might be hinting at, which is that by convention we assume that the speed of light is the same in all directions, but there are other conventions we can use as long as the round-trip speed of light agrees with that which we've measured (and yes, we can only ever measure the round-trip speed of light, FYI). Another convention is that all the light we see takes zero time to get to us but the light we emit goes out at half the speed one would expect with the standard convention (known as the Einstein synchronization convention). So instead of "light we see from Alpha Centauri is 4 years old" or "we see Alpha Centauri as it was 4 years ago" we can say that we see it as it is right now, but this is not a very commonly used convention.
https://booksforkeeps.co.uk/article/visiting-uncle-albert/
The intuition you can develop about special and general relativity from these books is pretty amazing!
In a lab setting, yes, but across such distances, no. Photons don't have a cycle counter on them, so they don't keep a cycle count and can't reveal that cycle count. All we can do is measure frequency/wavelength (spectrum, really, since we're going to see lots of photons, not really onesie/twosies) and intensity, and we can use the astrophysical distance ladder to figure out roughly where the emitter must have been.
It's not an easy task from the prospective of a photon, which can be easyly proven with just two little slits.
Experiencing time and having mass are linked in a very deep way. Objects that experience time, i.e. have some kind of state evolution, must have mass, this is how we know the neutrino has mass even though it's smaller than we can measure, because we measure them oscillating between the various flavours of nutrinos.
This is also how the Higgs mechanism gives rise to "rest mass" in most particles, by constantly exchanging weak hypercharge with them. This oscillation back and forth gives them mass.
I knew HN would nit my nit, well done!
So there must be a range in age. As some closer to still hot surface don't need to travel through parts of the sun.
During COVID, I had a lot of spare time and an aversion to reading the news or indeed anything on social media. So, I got interested in trying to wrap my head around the scale of the universe. I built an app called VOS - https://vos.ajmoon.com - which would plot things at scale on a map, allowing me to plan a walk (e.g. from the sun to Pluto) with various celestial objects at that scale. Then I made videos of some of those walk plans, explaining what you'd encounter. It was a lot of fun!
Wikipedia article: https://en.wikipedia.org/wiki/Near-Earth_supernova
Kurzgesagt video on the impact on Earth of supernovas at varying distances: https://www.youtube.com/watch?v=q4DF3j4saCE
As the Kurzesagt video points out, a supernova within 100 light-years would make space travel very difficult for humans and machines due to the immense amount of radiation for many years.
Still, I think the primary value is in expanding our understanding of science and the nature of the universe and our location within it.
Basing an inertial coordinate system on the observed positions of the bodies belonging to the Solar System is affected by much greater errors caused by the imperfect modeling of their relatively fast movements.
Using stars that are outside the Solar System is much better, but using distant extra-gallactic objects is even better.
If we did not have the "fixed" stars as a background on which to view the movements of the Sun, Moon and planets, who knows how many centuries later physics and technology would have reached the current level, because when seeing only the relative motions of the planets, without a fixed reference system, those are much harder to understand.
For interplanetary navigation, receiving signals from pulsars can be used as a backup or a replacement for atomic clocks. Individual pulsars, especially when young, are sometimes affected by "glitches" when their moment of inertia, thus the frequency of their signal, changes, but if multiple old pulsars are monitored, any glitches should be detectable and they should not affect operation.
Even the primitive humans of many thousands or tens of thousands of years ago knew to predict seasons by observing the rising stars and to navigate with the help of star gazing.
For the ancient civilizations dependent on agriculture, observing the stars, e.g. to determine when to sow various cultivated plants, could have a life and death impact, not a minor influence upon their life.
Most of the imaging and signal-processing tech built for astrophysics ends up in medicine, satellites, and everyday devices. The "wow" factor funds a lot of spinoffs.
Space weather doesn’t stop at the edge of the Solar System. Supernovae, stellar motions, even rogue objects can affect us. Better to understand them early.
It’s long-term thinking. Nobody builds interstellar ships tomorrow, but mapping the neighborhood now is how future generations avoid starting from zero.
Honestly, it also grounds us. Realizing Earth is one small rock among billions changes how seriously we treat our only habitable home.
Here's the one they say is from October 1999:
https://www.natgeomaps.com/hm-1999-the-universe
I remember this one was an updated version of a poster they published in the late 1970s or early 80s -- I had a copy on my wall in 1985.
Too bad we are in the current era of eschewing scientific research in favor of crony politics.
https://en.wikipedia.org/wiki/Breakthrough_Starshot
https://www.universetoday.com/articles/starshot-not-get-a-re...
Regarding the former, various studies have been made and will certainly continue to be made: https://en.wikipedia.org/wiki/Interstellar_travel#Designs_an...
Exploration of the Very Local Interstellar Medium (VLISM) will likely come first: https://link.springer.com/article/10.1007/s11214-022-00943-x
Also, I would love to see a lunar base happen in my lifetime
Our species is still very immature ethically, socially, and politically. We haven't even learned to accept each other and co-exist happily on Earth. Our distant hominin ancestors crossed entire continents but today we set up physical borders and cultural barriers to prevent even neighborly visits. We certainly won't become the broad-minded united ethical species that Star Trek TOS/TNG portrayed within the next 2-3 centuries.
Gradual spatial expansion, and through that, gradual cognitive and worldview expansion, has been our track record. Whenever things got hairy for someone in our hominin tree at any time, they moved just a little bit more to survive.
So, I feel exploring and settling other solar system bodies should be our next logical step. There are 4 solid planets, 5 dwarf planets, and as per Gemini, ~40 moons, ~3000 asteroid belt objects, and 200000+ Kuiper belt objects, all above 10 km radius. That's a lot of nearby space to explore and more practical than interstellar. Some of them will become the solutions or refuges from our current social and political problems on Earth.
It'll take us 1000s of years more, maybe even 100s of 1000s, to do all this. Including a lot of violence, conflicts and injustice. But eventually, we will learn to develop the cooperative institutions and cognitive/ethical frameworks we currently lack to become a multi-planet species. Interplanetary cooperative institutions and technologies will emerge eventually, just like today we have airplanes, the Internet, UN, WHO, EU - institutions and technologies that, while far from perfect, seemed downright unlikely for 100s of 1000s of years of our hominin history.
https://en.m.wikipedia.org/wiki/Radioisotope_thermoelectric_...
I’m not sure that we have the engineering ability to actually do that with any real chance of success after a 100 year deep space flight, or the willingness to wait that long to find out.
Does anyone else remember that or am I imagining it? I think it was like 10 years ago
I guess the sad reality is that these tools aren't that useful for anything but diagramming the odd interstellar rock.
https://chview.nova.org/solcom/index.html
edit: crossreference with https://gruze.org/galaxymap/map_2020/