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Slightly off-topic but I find it incredible that people in the comments think interstellar travel is impossible (or almost impossible) A couple centuries ago,

Slightly off-topic but I find it incredible that people in the comments think interstellar travel is impossible (or almost impossible) A couple centuries ago, the brightest minds thought that humans flying in the air would take a million years. How can humans travel to the other part of the earth within a month? Today, it takes 16 hours (4 of which are airport security). A century ago, almost everyone thought that stepping on a divine body like the moon is absolutely impossible for humanity. We did it less than 80 years after inventing aircrafts. A century ago, everyone thought it was impossible to fling a tiny device to blow up an entire city. Hiroshima and Nagasaki... Now, we think that it would be impossible to travel very long distances in space. Well, this challenge seems a piece of cake compared to flying in the air, walking on the moon, or generating unimaginable energy from atoms. My layman solution to interstellar travel is constant acceleration using controlled nuclear fusion. We can use interstellar dust for necessary matter for our nuclear fusion (lots of hydrogen in interstellar dust). Even if we can't use interstellar dust while travelling, we can certainly carry enough from our solar system. I read somewhere (don't remember where) that if a ship constantly accelerates in space, it can reach another star system in a few decades and another galaxy in less than a century. It's definitely a trivial challenge for humanity compared to what we have accomplished in the last 2 centuries. What do you think?

HyperSane 4y ago
Interstellar travel is downright easy on time scales of hundred to thousands of years. We just need to make humans last long enough.
- AlexanderTheGr8 4y ago
  [1]> According to wikipedia, interstellar travel at 1G would take approximately 1 year + the distance in lightyears. Proxima Centauri (4.2 light years) for example would take 5.2 years. This^ is from the traveller's standpoint. I am not completely sure about how long it would take from the perspective of someone on Earth. But this definitely seems plausible if we can solve the other problems with constant acceleration such as sufficient fuel and protection from interstellar dust (at close to light speed, dust would hit with unimaginable force). [1] https://space.stackexchange.com/questions/840/how-fast-will-1g-get-you-there https://space.stackexchange.com/questions/840/how-fast-will-...
  - HyperSane 4y ago
    Maintaining a 1G acceleration for years is either impossible or so hard it may as well be impossible. Even if you had a magic drive that could do it you would soon reach velocities where colliding with the smallest spec of dust would be like a small nuclear bomb. 1G to Proxima Centauri would reach a peak velocity of .95 c and hitting a 1g particle would release 48451 tons of TNT of energy. So you would need BOTH a magic drive and a magic shield.
tanbog5 4y ago
If interstellar travel is as "trivial" as you argue, then the great filter starts to look a lot more scary to me.
- AlexanderTheGr8 4y ago
  With the assumption that interstellar travel is trivial for a sufficiently advanced civilization, Fermi Paradox becomes a true problem. The best solution for Fermi Parafox, in my opinion, is interstellar travel being impossible. I don't think Dark Forest is possible because consider how different our thought process is from any other life form on Earth. And due to butterfly effect, every civilization's thinking will be completely different. The chances that every civilization will converge their thinking into dark forest seems impossible. Some stupid civilization is bound to broadcast their existence and location. Some other stupid civ might try to control all galaxies using self-replication (exponential growth). So we should have seen some such sign (considering how many alien civs are likely to be there) Great Filter is another possibility. But it feels unlikely : there are trillions (10^12) of galaxies and trillions (10^12) of planets in each galaxy. So a total of 10^24 (1,000,000,000,000,000,000,000,000) planets out there. Consider the number of civilizations. Is it possible for every single advanced civilization to be destroyed by the Great Filter? If it is, then it must be one hell of a filter. I am very excited to find out what it is, if it happens in my lifetime.
species9606 4y ago
> I read somewhere (don't remember where) that if a ship constantly accelerates in space, it can reach another star system in a few decades and another galaxy in less than a century. The problem is, it also has to slow down and stop at the destination. To do that, it would have to take all the deceleration fuel with it, and the amount of fuel needed goes up exponentially with the amount of deceleration required.[1] There’s no known or even theoretical form of propulsion with the specific impulse needed to get us to the next star system in under 600 years. [1] https://en.m.wikipedia.org/wiki/Tsiolkovsky_rocket_equation https://en.m.wikipedia.org/wiki/Tsiolkovsky_rocket_equation
- AlexanderTheGr8 4y ago
  I skipped over deceleration because 1) our probes can transmit something significant about a galaxy even at that speed and 2) over time, we can probably figure out a way to decelerate using a galaxy's natural resources (similar to how we use a planet's gravity for slingshot) Surely, given a century, our scientists will figure out something.
  - species9606 4y ago
    There aren’t any resources in interstellar space. It’s a near-perfect vacuum and the temperature is a uniform 3 Kelvins.
    - AlexanderTheGr8 4y ago
      There are huge swaths of interstellar dust (mostly hydrogen) which can be used to slow the probe down. If not, then we can use a galaxy's resources to slow us down. Basically a complex version of planetary-slingshot. My argument is, given a century, we are likely to be able to find some way to decelerate. Consider our accomplishments in the last century (airflight, spaceflight, computers, nuclear, internet)
  - NovaVeles 4y ago
    Sorry this may seem a little snarky but - "They will think of something" - the universal band-aid for I want it to be true but I rationally don't know how. When ever I hear that, the optimist in me wants it to be true. The pessimist thinks otherwise and nowadays the pessimist usually wins. We will have hotels in orbit by the 1970's - they will think of something! That was a legitimate thing that the Hiltons proposed back in the 1960's.
namlem 4y ago
Using fusion for interstellar travel could work, but it would be extremely slow due to the low availability of fuel. Maybe it could be done for synthetic lifeforms or cryonic preservation. Generation ships and such are out of the question though.
- AlexanderTheGr8 4y ago
  > low availability of fuel Isn't hydrogen one of the most common elements in the universe? And nuclear fusion needs only hydrogen (technically deuterium and tritium, but where there's hydrogen, deuterium and tritium will also be there)
  - moloch-hai 4y ago
    Sorry, no tritium.
dboreham 4y ago
Magical thinking unfortunately.
- AlexanderTheGr8 4y ago
  what is magical thinking? Interstellar travel being possible or impossible?
NovaVeles 4y ago
I think the big thing is that all those original achievement don't defy physics to achieve them. It was a case of ignorance and the belief that we just were not that smart. And while there was a big period of exponential growth - there is an upper limit. We aren't going to Galaxies in a few hundred years - the time to Andromeda is 2.5 Million Light Years. Unless we fundamentally have physics wrong, we aren't doing that any quicker no matter how hard we try.
- antupis 4y ago
  2.5 million years earth time but ship time is totally different.
  - moloch-hai 4y ago
    Imagine being blasted with 2.5M years' worth of relativistic IGM protons in only a few years of ship time.
- deleted 4y ago
  [deleted]
avz 4y ago
Side note: Sorry to spoil the apparently impeccable record, but for completeness: A half-century ago, civilians could experience supersonic flight. Well, it has since become impossible. A half-century ago, people walked on the Moon. And not once since. Just a reminder then that unfortunately the passage of time alone is insufficient to guarantee technological progress. Now, let's get back to work, I guess...
- AlexanderTheGr8 4y ago
  you are right about this, but my argument is that we can do this if we want to. Whenever humanity set its sights on a big project such as Apollo or Manhattan, we have accomplished "impossible" things.
  - ianai 4y ago
    Human history is one of both pessimism and optimism. Definitely the optimism of the US in the 1950s and 60s was helped along by the destitution of the Great Depression (1930s+) and WWII. And there was still a lot of suffering and reason to be pessimistic in that time. (And the 30s were a direct result of the 20s.) I’ve also seen the studies on human cycles suggesting a link between how long ago a period of massive suffering occurred and the propensity for people to entertain ideas likely to bring about great suffering. Simply, people unable to forget the horribleness of war will fend off the little and big things that can lead to war much better than people who have never seen war. I hope humanity can regain some optimism and direction without having to go through a world war. Or similar. I find it worrying how much modern fiction is dystopian. I would call Game of Thrones dystopian, for instance, and it was immensely popular. Utopias like Star Trek are often ridiculed, for counterpoint. Granted, internet comments are generally worthless. The signal to noise ratio in HN comments has gotten extra horrible of late, for that matter. It could be just the low lying fruit for people to get upvotes. But it degrades the site.
- dopidopHN 4y ago
  Absolutely. I wonder if say, cheap energy, will be as readily available for non gov / army purposes in 50 years. The comment your responding too sound like someone born in the 60´s or 50’s. ( meaning : tech is always progressing, no limit, forward and upward . It’s nice. But I don’t think it match 2023 )
samplatt 4y ago
>A century ago, almost everyone thought that stepping on a divine body like the moon is absolutely impossible for humanity. A century ago we DEFINITELY conceived of visiting a divine body. 121 years ago a science fiction movie about landing on the moon was released, based on a scifi book released _158_ years ago. >if a ship constantly accelerates in space, it can reach another star system in a few decades Try a few dozen thousand years, my dude... https://www.universetoday.com/141407/how-big-would-a-generation-ship-need-to-be-to-keep-a-crew-of-500-alive-for-the-journey-to-another-star-1/ https://www.universetoday.com/141407/how-big-would-a-generat... Even Project Orion, which is literally strapping many successive nuclear bombs onto the bottom of your craft, would take 130 years to get to our closest star.... and that's not taking into account stopping time, so it'd take 130 years to do a flyby of Alpha Centauri at 3% of the speed of light. Not to mention the fact that ALL spaceships bleed air even under optimum conditions. A generational ship would need to be HUGE and have even bigger reserve supplies of air and water than you'd ever think possible. 50,000 years worth of air and water for 100-500 people? That's a LOT of mass. Beyond ion propulsion and Project Orion we start to get into wormholes, black-hole-gravity-assists, remote-quantum-entanglement, time travel. Stuff that's theoretically possible kinda sorta if you completely ignore some fairly fundamental laws... the tricky thing is EVEN IF you choose to ignore those fundamental laws, the amount of sheer energy you're talking about is like the many multiples of the energy output of our sun over its _entire lifetime_.
- AlexanderTheGr8 4y ago
  > A century ago we DEFINITELY conceived of visiting a divine body. 121 years ago a science fiction movie about landing on the moon was released, based on a scifi book released _158_ years ago. I said "almost everyone". If you go to 1920s and ask a million people if humanity will be able to walk on the moon within their lifetimes, not a single one would say yes. And yet, we were able to do it. Similarly, we have been conceiving of interstellar travel for decades. > Try a few dozen thousand years, my dude With constant acceleration, ship time is very different. With constant acceleration using controlled nuclear fusion, we can do it in less than a century. Project Orion is not constant acceleration. Now before you point out issues in constant acceleration, remember that if you were in 1920s, you (and I) would also point out issues in moon landing. How can humanity ever leave Earth's gravity, go accurately to the moon, decelerate, LAND without crashing, walk, LAUNCH from moon again, go accurately to the earth, handle extreme atmospheric temps, and LAND without crashing. Well, we did all of that. So surely, given a century, we can figure out interstellar travel.
avz 4y ago
I agree with your conclusion, but I always find that these discussions miss the role of medical science. The key parameters governing feasibility of human interstellar travel are the average human lifespan in years and typical interstellar distance in lightyears. These are roughly 72 years and 5 lightyears, respectively. So it takes about 70% of a human lifespan to travel a typical interstellar distance at 10% of the speed of light. This is... not great. The key realization is that the relationship of these two numbers is in a sense an accident of biology and astronomy. It is usually assumed that future technological progress might enable travel at a large fraction of the speed of light, but it is often missed that future medical progress might extend human lifespan to say 400 or 1000 years. A scarier realization is that intelligent aliens might have natural lifespan that make interstellar travel seem far more practical.
- moloch-hai 4y ago
  https://cantrip.org/slow.pdf https://cantrip.org/slow.pdf
- AlexanderTheGr8 4y ago
  Human hibernation should be able to solve that problem. I know I am asking for too many things but the challenges for the Apollo mission were even more extravagant. They had to figure out how to launch from earth's gravity, go exactly to the moon, decelerate, land without accident, launch back again, go exactly to the earth, decelerate and land without accident. Atmospheric reentry is almost 25000 degree Celsius, hotter than almost anything we had ever experienced. So, given a century, surely medicine will figure out hibernation. And then humans can continue their lifespan when they reach their destination.
0110101001 4y ago
I think the difference is that your historical examples of skepticism (which are a bit exaggerated, btw. Da Vinci was a pretty bright guy who thought human flight was possible; Churchill summed up the current understanding of nuclear physics 99 years ago as "Might not a bomb no bigger than an orange be found to possess a secret power... to concentrate the force of a thousand tons of cordite and blast a township at a stroke?"; Konstantin Tsiolkovsky described the science of space travel by rocket in The Exploration of Cosmic Space by Means of Reaction Devices back in 1898)... your examples of skepticism are based on ignorance, not science. As far as I'm aware, nobody ever had a scientific rationale to think humans couldn't achieve flight. If so, it was obviously extremely flawed. We have well-supported science to support the idea that interstellar travel at human timescales isn't possible. But any scientist will also tell you that there are potential methods to achieve interstellar travel that are consistent with our laws of physics. It's just that, unlike your examples, it's not a matter of human ingenuity to find them. It's a matter of the very nature of our universe whether things like wormholes or negative energy exist or not.
avz 4y ago
I think the situation with interstellar travel is well summed up in this conversation between TARS and Cooper as they attempt to dock at Endurance (intentional pun hiding in movie title): TARS: It's not possible. Cooper: No, it's necessary. It seems impossible, but if we don't pull it off we die. And I don't mean we the few folks on HN. I mean everyone. Earth is a graveyard of species. Nearly all (99% IIRC) species that ever existed have gone extinct (most before we showed up). As a species, we can't stay here and live. A 9-mile thin layer of gas over a single small planet is just not a reliable long-term basis of survival. In fact, the fragility of our tiny little habitant is on display right in front of us this century.
- AlexanderTheGr8 4y ago
  tbh I never really understood that conversation. TARS is a machine and if it's impossible from an advanced machine's standpoint, it's impossible from a physics standpoint. Cooper's maneuver was pretty simple that TARS should have been able to simulate and figure out. Regardless, I agree that being multi-planetary is absolutely a requirement for humanity. We are too risky here. And the risk is not from outside. Humanity has survived for 100s of millions of years without as asteroid annihilating us, and I don't see it changing now). The biggest risk to humanity is humanity. We will probably figure out a way to destroy ourselves, either with something much more powerful than nuclear bombs or some new unimaginable tech.
  - avz 4y ago
    Single planetary system isn't much more of a protection than a single planet against some of the possible extinction events, e.g. ones associated with the activity of the Sun or intelligent aliens. > Humanity has survived for 100s of millions of years without as asteroid annihilating us, and I don't see it changing now). Homo sapiens is thought to have existed for mere 300,000 years. Our last common ancestor with the chimpanzee [1] existed no more than 13 million years ago. K-T extinction event [2] that wiped out dinosaurs happened 66 million years ago. There have been numerous extinction events before and after that [3]. On the timescales of species this planet isn't safe. At these timescales rare events become regular occurrences. [1]: https://en.wikipedia.org/wiki/Chimpanzee%E2%80%93human_last_common_ancestor https://en.wikipedia.org/wiki/Chimpanzee%E2%80%93human_last_... [2]: https://en.wikipedia.org/wiki/Cretaceous%E2%80%93Paleogene_extinction_event https://en.wikipedia.org/wiki/Cretaceous%E2%80%93Paleogene_e... [3]: https://en.wikipedia.org/wiki/List_of_extinction_events https://en.wikipedia.org/wiki/List_of_extinction_events
aardvark179 4y ago
Every time this topic comes up somebody suggests constant acceleration, and every time somebody has to point out that even if you don’t want to decelerate the relativistic rocket equation is still a very harsh mistress. Remember you don’t just have to carry the fuel to accelerate your payload, you have to accelerate the fuel as well. You may say, “Oh, but I could use a laser to accelerate my craft, that way I don’t need to carry the fuel on board,” and the amount of energy required is still going to be a hell of a lot more than you think.
elorant 4y ago
There’s one thing about interstellar travel you should bear in mind. If you plan on visiting an alien world you should take into consideration the time needed to decelerate. And once you start decelerating, time dilation will gradually stop and you’ll spend an eternity getting to your destination.
deleted 4y ago
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- deleted 4y ago
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pvg 4y ago
A couple centuries ago, the brightest minds thought that humans flying in the air would take a million years. Two centuries ago humans actually flew. A century ago, almost everyone thought that stepping on a divine body like the moon Nobody seriously thought the moon was a 'divine body' a century ago. The rocket equation was known and understood to form a possible theoretical basis for interplanetary travel technology. A century ago, everyone thought it was impossible to fling a tiny device to blow up an entire city. HG Wells thought it was possible as did many others. https://www.bbc.com/news/magazine-33365776 https://www.bbc.com/news/magazine-33365776 "Churchill grasped the danger of technology running ahead of human maturity, penning a 1924 article in the Pall Mall Gazette called "Shall we all commit suicide?". In the article, Churchill wrote: "Might a bomb no bigger than an orange be found to possess a secret power to destroy a whole block of buildings - nay to concentrate the force of a thousand tons of cordite and blast a township at a stroke?"" Now, we think that it would be impossible to travel very long distances in space. Well, this challenge seems a piece of cake compared to flying in the air, walking on the moon, or generating unimaginable energy from atoms. We think it's very difficult compared to the challenge of flying through the air or walking on the moon or generating energy from atoms in part because we understand those past challenges and can reasonably compare it to something like interstellar travel. It is decidedly nontrivial.

HyperSane 4y ago

Interstellar travel is downright easy on time scales of hundred to thousands of years. We just need to make humans last long enough.

AlexanderTheGr8 4y ago
[1]> According to wikipedia, interstellar travel at 1G would take approximately 1 year + the distance in lightyears. Proxima Centauri (4.2 light years) for example would take 5.2 years. This^ is from the traveller's standpoint. I am not completely sure about how long it would take from the perspective of someone on Earth. But this definitely seems plausible if we can solve the other problems with constant acceleration such as sufficient fuel and protection from interstellar dust (at close to light speed, dust would hit with unimaginable force). [1] https://space.stackexchange.com/questions/840/how-fast-will-1g-get-you-there https://space.stackexchange.com/questions/840/how-fast-will-...
- HyperSane 4y ago
  Maintaining a 1G acceleration for years is either impossible or so hard it may as well be impossible. Even if you had a magic drive that could do it you would soon reach velocities where colliding with the smallest spec of dust would be like a small nuclear bomb. 1G to Proxima Centauri would reach a peak velocity of .95 c and hitting a 1g particle would release 48451 tons of TNT of energy. So you would need BOTH a magic drive and a magic shield.

tanbog5 4y ago

If interstellar travel is as "trivial" as you argue, then the great filter starts to look a lot more scary to me.

AlexanderTheGr8 4y ago
With the assumption that interstellar travel is trivial for a sufficiently advanced civilization, Fermi Paradox becomes a true problem. The best solution for Fermi Parafox, in my opinion, is interstellar travel being impossible. I don't think Dark Forest is possible because consider how different our thought process is from any other life form on Earth. And due to butterfly effect, every civilization's thinking will be completely different. The chances that every civilization will converge their thinking into dark forest seems impossible. Some stupid civilization is bound to broadcast their existence and location. Some other stupid civ might try to control all galaxies using self-replication (exponential growth). So we should have seen some such sign (considering how many alien civs are likely to be there) Great Filter is another possibility. But it feels unlikely : there are trillions (10^12) of galaxies and trillions (10^12) of planets in each galaxy. So a total of 10^24 (1,000,000,000,000,000,000,000,000) planets out there. Consider the number of civilizations. Is it possible for every single advanced civilization to be destroyed by the Great Filter? If it is, then it must be one hell of a filter. I am very excited to find out what it is, if it happens in my lifetime.

species9606 4y ago

> I read somewhere (don't remember where) that if a ship constantly accelerates in space, it can reach another star system in a few decades and another galaxy in less than a century. The problem is, it also has to slow down and stop at the destination. To do that, it would have to take all the deceleration fuel with it, and the amount of fuel needed goes up exponentially with the amount of deceleration required.[1] There’s no known or even theoretical form of propulsion with the specific impulse needed to get us to the next star system in under 600 years. [1] https://en.m.wikipedia.org/wiki/Tsiolkovsky_rocket_equation https://en.m.wikipedia.org/wiki/Tsiolkovsky_rocket_equation

AlexanderTheGr8 4y ago
I skipped over deceleration because 1) our probes can transmit something significant about a galaxy even at that speed and 2) over time, we can probably figure out a way to decelerate using a galaxy's natural resources (similar to how we use a planet's gravity for slingshot) Surely, given a century, our scientists will figure out something.
- species9606 4y ago
  There aren’t any resources in interstellar space. It’s a near-perfect vacuum and the temperature is a uniform 3 Kelvins.
  - AlexanderTheGr8 4y ago
    There are huge swaths of interstellar dust (mostly hydrogen) which can be used to slow the probe down. If not, then we can use a galaxy's resources to slow us down. Basically a complex version of planetary-slingshot. My argument is, given a century, we are likely to be able to find some way to decelerate. Consider our accomplishments in the last century (airflight, spaceflight, computers, nuclear, internet)
- NovaVeles 4y ago
  Sorry this may seem a little snarky but - "They will think of something" - the universal band-aid for I want it to be true but I rationally don't know how. When ever I hear that, the optimist in me wants it to be true. The pessimist thinks otherwise and nowadays the pessimist usually wins. We will have hotels in orbit by the 1970's - they will think of something! That was a legitimate thing that the Hiltons proposed back in the 1960's.

namlem 4y ago

Using fusion for interstellar travel could work, but it would be extremely slow due to the low availability of fuel. Maybe it could be done for synthetic lifeforms or cryonic preservation. Generation ships and such are out of the question though.

AlexanderTheGr8 4y ago
> low availability of fuel Isn't hydrogen one of the most common elements in the universe? And nuclear fusion needs only hydrogen (technically deuterium and tritium, but where there's hydrogen, deuterium and tritium will also be there)
- moloch-hai 4y ago
  Sorry, no tritium.

dboreham 4y ago

Magical thinking unfortunately.

AlexanderTheGr8 4y ago
what is magical thinking? Interstellar travel being possible or impossible?

NovaVeles 4y ago

I think the big thing is that all those original achievement don't defy physics to achieve them. It was a case of ignorance and the belief that we just were not that smart. And while there was a big period of exponential growth - there is an upper limit. We aren't going to Galaxies in a few hundred years - the time to Andromeda is 2.5 Million Light Years. Unless we fundamentally have physics wrong, we aren't doing that any quicker no matter how hard we try.

antupis 4y ago
2.5 million years earth time but ship time is totally different.
- moloch-hai 4y ago
  Imagine being blasted with 2.5M years' worth of relativistic IGM protons in only a few years of ship time.
deleted 4y ago
[deleted]

avz 4y ago

Side note: Sorry to spoil the apparently impeccable record, but for completeness: A half-century ago, civilians could experience supersonic flight. Well, it has since become impossible. A half-century ago, people walked on the Moon. And not once since. Just a reminder then that unfortunately the passage of time alone is insufficient to guarantee technological progress. Now, let's get back to work, I guess...

AlexanderTheGr8 4y ago
you are right about this, but my argument is that we can do this if we want to. Whenever humanity set its sights on a big project such as Apollo or Manhattan, we have accomplished "impossible" things.
- ianai 4y ago
  Human history is one of both pessimism and optimism. Definitely the optimism of the US in the 1950s and 60s was helped along by the destitution of the Great Depression (1930s+) and WWII. And there was still a lot of suffering and reason to be pessimistic in that time. (And the 30s were a direct result of the 20s.) I’ve also seen the studies on human cycles suggesting a link between how long ago a period of massive suffering occurred and the propensity for people to entertain ideas likely to bring about great suffering. Simply, people unable to forget the horribleness of war will fend off the little and big things that can lead to war much better than people who have never seen war. I hope humanity can regain some optimism and direction without having to go through a world war. Or similar. I find it worrying how much modern fiction is dystopian. I would call Game of Thrones dystopian, for instance, and it was immensely popular. Utopias like Star Trek are often ridiculed, for counterpoint. Granted, internet comments are generally worthless. The signal to noise ratio in HN comments has gotten extra horrible of late, for that matter. It could be just the low lying fruit for people to get upvotes. But it degrades the site.
dopidopHN 4y ago
Absolutely. I wonder if say, cheap energy, will be as readily available for non gov / army purposes in 50 years. The comment your responding too sound like someone born in the 60´s or 50’s. ( meaning : tech is always progressing, no limit, forward and upward . It’s nice. But I don’t think it match 2023 )

samplatt 4y ago

>A century ago, almost everyone thought that stepping on a divine body like the moon is absolutely impossible for humanity. A century ago we DEFINITELY conceived of visiting a divine body. 121 years ago a science fiction movie about landing on the moon was released, based on a scifi book released _158_ years ago. >if a ship constantly accelerates in space, it can reach another star system in a few decades Try a few dozen thousand years, my dude... https://www.universetoday.com/141407/how-big-would-a-generation-ship-need-to-be-to-keep-a-crew-of-500-alive-for-the-journey-to-another-star-1/ https://www.universetoday.com/141407/how-big-would-a-generat... Even Project Orion, which is literally strapping many successive nuclear bombs onto the bottom of your craft, would take 130 years to get to our closest star.... and that's not taking into account stopping time, so it'd take 130 years to do a flyby of Alpha Centauri at 3% of the speed of light. Not to mention the fact that ALL spaceships bleed air even under optimum conditions. A generational ship would need to be HUGE and have even bigger reserve supplies of air and water than you'd ever think possible. 50,000 years worth of air and water for 100-500 people? That's a LOT of mass. Beyond ion propulsion and Project Orion we start to get into wormholes, black-hole-gravity-assists, remote-quantum-entanglement, time travel. Stuff that's theoretically possible kinda sorta if you completely ignore some fairly fundamental laws... the tricky thing is EVEN IF you choose to ignore those fundamental laws, the amount of sheer energy you're talking about is like the many multiples of the energy output of our sun over its _entire lifetime_.

AlexanderTheGr8 4y ago
> A century ago we DEFINITELY conceived of visiting a divine body. 121 years ago a science fiction movie about landing on the moon was released, based on a scifi book released _158_ years ago. I said "almost everyone". If you go to 1920s and ask a million people if humanity will be able to walk on the moon within their lifetimes, not a single one would say yes. And yet, we were able to do it. Similarly, we have been conceiving of interstellar travel for decades. > Try a few dozen thousand years, my dude With constant acceleration, ship time is very different. With constant acceleration using controlled nuclear fusion, we can do it in less than a century. Project Orion is not constant acceleration. Now before you point out issues in constant acceleration, remember that if you were in 1920s, you (and I) would also point out issues in moon landing. How can humanity ever leave Earth's gravity, go accurately to the moon, decelerate, LAND without crashing, walk, LAUNCH from moon again, go accurately to the earth, handle extreme atmospheric temps, and LAND without crashing. Well, we did all of that. So surely, given a century, we can figure out interstellar travel.

avz 4y ago

I agree with your conclusion, but I always find that these discussions miss the role of medical science. The key parameters governing feasibility of human interstellar travel are the average human lifespan in years and typical interstellar distance in lightyears. These are roughly 72 years and 5 lightyears, respectively. So it takes about 70% of a human lifespan to travel a typical interstellar distance at 10% of the speed of light. This is... not great. The key realization is that the relationship of these two numbers is in a sense an accident of biology and astronomy. It is usually assumed that future technological progress might enable travel at a large fraction of the speed of light, but it is often missed that future medical progress might extend human lifespan to say 400 or 1000 years. A scarier realization is that intelligent aliens might have natural lifespan that make interstellar travel seem far more practical.

moloch-hai 4y ago
https://cantrip.org/slow.pdf https://cantrip.org/slow.pdf
AlexanderTheGr8 4y ago
Human hibernation should be able to solve that problem. I know I am asking for too many things but the challenges for the Apollo mission were even more extravagant. They had to figure out how to launch from earth's gravity, go exactly to the moon, decelerate, land without accident, launch back again, go exactly to the earth, decelerate and land without accident. Atmospheric reentry is almost 25000 degree Celsius, hotter than almost anything we had ever experienced. So, given a century, surely medicine will figure out hibernation. And then humans can continue their lifespan when they reach their destination.

0110101001 4y ago

I think the difference is that your historical examples of skepticism (which are a bit exaggerated, btw. Da Vinci was a pretty bright guy who thought human flight was possible; Churchill summed up the current understanding of nuclear physics 99 years ago as "Might not a bomb no bigger than an orange be found to possess a secret power... to concentrate the force of a thousand tons of cordite and blast a township at a stroke?"; Konstantin Tsiolkovsky described the science of space travel by rocket in The Exploration of Cosmic Space by Means of Reaction Devices back in 1898)... your examples of skepticism are based on ignorance, not science. As far as I'm aware, nobody ever had a scientific rationale to think humans couldn't achieve flight. If so, it was obviously extremely flawed. We have well-supported science to support the idea that interstellar travel at human timescales isn't possible. But any scientist will also tell you that there are potential methods to achieve interstellar travel that are consistent with our laws of physics. It's just that, unlike your examples, it's not a matter of human ingenuity to find them. It's a matter of the very nature of our universe whether things like wormholes or negative energy exist or not.

avz 4y ago

I think the situation with interstellar travel is well summed up in this conversation between TARS and Cooper as they attempt to dock at Endurance (intentional pun hiding in movie title): TARS: It's not possible. Cooper: No, it's necessary. It seems impossible, but if we don't pull it off we die. And I don't mean we the few folks on HN. I mean everyone. Earth is a graveyard of species. Nearly all (99% IIRC) species that ever existed have gone extinct (most before we showed up). As a species, we can't stay here and live. A 9-mile thin layer of gas over a single small planet is just not a reliable long-term basis of survival. In fact, the fragility of our tiny little habitant is on display right in front of us this century.

AlexanderTheGr8 4y ago
tbh I never really understood that conversation. TARS is a machine and if it's impossible from an advanced machine's standpoint, it's impossible from a physics standpoint. Cooper's maneuver was pretty simple that TARS should have been able to simulate and figure out. Regardless, I agree that being multi-planetary is absolutely a requirement for humanity. We are too risky here. And the risk is not from outside. Humanity has survived for 100s of millions of years without as asteroid annihilating us, and I don't see it changing now). The biggest risk to humanity is humanity. We will probably figure out a way to destroy ourselves, either with something much more powerful than nuclear bombs or some new unimaginable tech.
- avz 4y ago
  Single planetary system isn't much more of a protection than a single planet against some of the possible extinction events, e.g. ones associated with the activity of the Sun or intelligent aliens. > Humanity has survived for 100s of millions of years without as asteroid annihilating us, and I don't see it changing now). Homo sapiens is thought to have existed for mere 300,000 years. Our last common ancestor with the chimpanzee [1] existed no more than 13 million years ago. K-T extinction event [2] that wiped out dinosaurs happened 66 million years ago. There have been numerous extinction events before and after that [3]. On the timescales of species this planet isn't safe. At these timescales rare events become regular occurrences. [1]: https://en.wikipedia.org/wiki/Chimpanzee%E2%80%93human_last_common_ancestor https://en.wikipedia.org/wiki/Chimpanzee%E2%80%93human_last_... [2]: https://en.wikipedia.org/wiki/Cretaceous%E2%80%93Paleogene_extinction_event https://en.wikipedia.org/wiki/Cretaceous%E2%80%93Paleogene_e... [3]: https://en.wikipedia.org/wiki/List_of_extinction_events https://en.wikipedia.org/wiki/List_of_extinction_events

aardvark179 4y ago

Every time this topic comes up somebody suggests constant acceleration, and every time somebody has to point out that even if you don’t want to decelerate the relativistic rocket equation is still a very harsh mistress. Remember you don’t just have to carry the fuel to accelerate your payload, you have to accelerate the fuel as well. You may say, “Oh, but I could use a laser to accelerate my craft, that way I don’t need to carry the fuel on board,” and the amount of energy required is still going to be a hell of a lot more than you think.

elorant 4y ago

There’s one thing about interstellar travel you should bear in mind. If you plan on visiting an alien world you should take into consideration the time needed to decelerate. And once you start decelerating, time dilation will gradually stop and you’ll spend an eternity getting to your destination.

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pvg 4y ago

A couple centuries ago, the brightest minds thought that humans flying in the air would take a million years. Two centuries ago humans actually flew. A century ago, almost everyone thought that stepping on a divine body like the moon Nobody seriously thought the moon was a 'divine body' a century ago. The rocket equation was known and understood to form a possible theoretical basis for interplanetary travel technology. A century ago, everyone thought it was impossible to fling a tiny device to blow up an entire city. HG Wells thought it was possible as did many others. https://www.bbc.com/news/magazine-33365776 https://www.bbc.com/news/magazine-33365776 "Churchill grasped the danger of technology running ahead of human maturity, penning a 1924 article in the Pall Mall Gazette called "Shall we all commit suicide?". In the article, Churchill wrote: "Might a bomb no bigger than an orange be found to possess a secret power to destroy a whole block of buildings - nay to concentrate the force of a thousand tons of cordite and blast a township at a stroke?"" Now, we think that it would be impossible to travel very long distances in space. Well, this challenge seems a piece of cake compared to flying in the air, walking on the moon, or generating unimaginable energy from atoms. We think it's very difficult compared to the challenge of flying through the air or walking on the moon or generating energy from atoms in part because we understand those past challenges and can reasonably compare it to something like interstellar travel. It is decidedly nontrivial.