I also wonder about rogue planets near the galactic center. They wouldn't need to have their own star to get bathed in plenty of light from other nearby stars.
There would be no such thing as night and day either.
Water is pretty good at blocking radiation [1]. Life could exist in a layer of the ocean where ionizing radiation is reduced to a survivable level but plenty of visible light gets through.
It isn't a great source, but this seems to suggest it would actually be pretty significant:
> "Near the galactic center, the average distance between neighboring stars would be only 1000 AU (about a light-week). If the Sun were located within a parsec of the galactic center, there would be a million stars in our sky with apparent brightness greater than Sirius. The total starlight in the night sky would be about 200 times greater than the light of the full moon; you could easily read the newspaper at midnight, relying on starlight alone."
Obviously this is not a perfect comparison, but even on Earth, if the night is cloudless, you are away from any cities, and the moon is not visible, the stars provide some light. Not bright enough to see clearly, but you can see a little bit, even with our weak human eyes. So I imagine that even on a planet without a star it wouldn't be 100% dark, there would be some light.
Just think about the early universe, a rouge planet would only need a sufficiently thick atmosphere. The universe itself would have been so hot that liquid water would have existed without a star's heat.
What sort of speed might some of these rogue planets be moving at? While the faster they move, the harder it would be to 'latch on' to a stable orbit / land, could they more than a waypoint to distant stars - might they be a 'spaceship'?
Although this would require us to 1) discover a dark planet, 2) moving at an appreciable percent of lightspeed, 3) with enough time to reach it, and 4) heading in the right direction so we could alight at a nearby solar system. If colonization sounds hard, how about those hitchhiking odds - infinitely improbable!
No, there shouldn't be any rouge planets moving fast enough. Stars at our distance from the galactic center move at roughly 230 km/s, with relative speeds of 10-30 km/s. The escape velocity from the galaxy is ~550 km/s, which is something like 0.2% light speed. Very few objects get accelerated above this speed, and when they do they leave the galaxy (so the probability that we pass one going by is negligible).
The discovery of hypervelocity stars (HVS) leaving our galaxy with speeds of
nearly $10^{3}$ km s$^{-1}$ has provided strong evidence towards the existence
of a massive compact object at the galaxy's center. HVS ejected via the
disruption of stellar binaries can occasionally yield a star with $v_{\infty}
\lesssim 10^4$ km s$^{-1}$, here we show that this mechanism can be extended to
massive black hole (MBH) mergers, where the secondary star is replaced by a MBH
with mass $M_2 \gtrsim 10^5 M_{\odot}$. We find that stars that are originally
bound to the secondary MBH are frequently ejected with $v_{\infty} > 10^4$ km
s$^{-1}$, and occasionally with velocities $\sim 10^5$ km s$^{-1}$ (one third the
speed of light), for this reason we refer to stars ejected from these systems
as "semi-relativistic" hypervelocity stars (SHS).
> There could also be hypervelocity planets, right?
There could definitely be hypervelocity planets just like planets. However, the density of these drops dramatically as you increase the speed you're looking for above the "typical" speed at our galactic radius (~230 km/s), simply because they are created by chance events. I believe the density of rouge planets is supposed to be of order the average density of normal planets in the galaxy (i.e., there might be 3 times as many rouge planets, but not 100 times as many). So finding a relativistic rouge planet nearby enough to be useful has negligible probability. (They are created by close encounters with black holes, after all.)
> Catching up to them would be hard, though.
Well, if you're thinking about using them as "space ships", you need to get up to speed anyways (since the alternative is to just travel on your own).
If you could catch one, your itinerant colony would have resources at speed for interstellar travel. You'd only need to accelerate a relatively small ship. And those resources would include mass for decelerating your ship at destination. But you couldn't stop for very long, without losing your ride.
"Most of Earth’s internal heat was delivered by the giant collisions that built the planet, a large portion of which remains locked inside its crust. This heat slowly trickles to the surface, providing a source of internal energy that has endured since the Earth formed. This interior heat will last for billions of years to come, but it’s a puny amount of energy, 3,000 times smaller than the sunlight that blasts the Earth daily."
Do this mean 3,000 times less than the Suns total daily output, or 3,000 times less than the sunlight that physically hits the earth daily?
I suspect the latter, but I still find this surprising. If daily sunshine hitting the earth is so massive then let's make solar work! If we could just collect even a fraction..
> Most of Earth’s internal heat was delivered by the giant collisions that built the planet, a large portion of which remains locked inside its crust.
In 19th century, Lord Kelvin estimated the age of Earth using this method, arriving at somewhere between 20 and 400 million years[1], much shorter than 4.6 billion years currently accepted. It turns out radioactive decay keeps the Earth's inside warm for a much longer time. (I.e., assuming Kelvin's calculation was correct, without radioactivity the Earth's core would have frozen over within the first 400M years.)
The Earth is quite a lot smaller that 1/3000th the volume of the Sun. If it was producing 1/3000th the total energy output of the Sun, it would explode.
I don't doubt that you're right, but to play devil's advocate Earth's surface to volume ratio is also much higher than the sun's so it cools quicker too.
This makes a kind of sense in terms of heat transfer: the sun's got a whole lot more insides for radiation to get through before it can even reach the surface to escape.
Perhaps, and furthermore Earth's surface-to-volume ratio would increase quite a lot more shortly afterward, as its shattered remains spread throughout the solar system. I imagine that the Earth would cool off rather quickly, or what's left of it anyway.
The word "daily" shouldn't have been in the original sentence. That makes it ludicrously wrong. (The total heat energy stored in the earth vastly exceeds the daily solar flux.)
Instead, it should be saying:
"The solar energy flux is 3000 times greater than the surface heat flux from interior heat."
At the moment, the most feasible way I see to the stars is via laser-launched ship. The cruel mistress that is the rocket equations don't favor even a self-contained starship driven by 100% efficient antimatter reactions, to say nothing of things that might actually work. Leaving your engine behind is almost a necessity. But even if you try to launch things from a solar-system based laser station the physics still don't really work out well. Light-years is a long way to maintain a focus for the beam.
Some have decided this means star travel is impossible; I say it just limits how quickly we can do it. We could launch very large ice asteroids with nanotech unmanned fusion stations that construct lasers ("vigorous handwave about magic here") and create ourselves a series of stepping stones to a star. It would take a long time, not least of which is because we would also need to set up the "stepping stones" to stop us on the other end, too! But in theory it seems like it would "just" be a matter of time. Lots of time. But a whole star system on the other end! It's a pretty big payoff for a strapping young Kardashev II civilization.
(Note that "just send information" only works after you deliver a physical package to the other end which would be capable of receiving it and doing something with it, and even nanotech is unlikely to be able to land anywhere to begin its lengthy self-replicating process to bootup civilization on the other end if it's merrily passing through a system at 80% the speed of light relative to the local rest frame.)
If you were lucky enough to stumble on to one of these planets in the way, it would provide a pretty nice shortcut to setting up your bridge by providing you a nice, huge power source (if you can find a lot of hydrogen lying around somewhere, which is a reasonable guess) that's already more-or-less at rest in the galactic frame, allowing you to use it to relatively easily create more stages on the enormous pipeline, and allowing you the ability to relatively easily replenish the stages in the middle. (If that's even desirable... perhaps the stages can be retargeted to other stars or something once the bootstrap package is successfully delivered.)
... of course, the article's starting with "10,000 years in the future" is probably not a terrible guess about all this, as such things go. This is a guaranteed-slow process, trading time for space. Tell your great-grandchildren to ask their great-grandchildren how the initial plans to make the initial plans for all this are going, and say "hi" to the future for you. Saying "we" will do this might very well be considered to be rather impudent of me, much like Napoleon trying to claim some sort of perceptible credit for the Hoover Dam.
It is possible for an observer to accelerate uniformly from their own perspective for an indefinite period of time in special relativity (the motion traces out a hyperbola in spacetime asymptotic to the lightcone). The person undergoing the acceleration doesn't notice anything changing as time goes on. All of the relativistic slowing down and time dilation effects etc. that you mention are seen in an inertial reference frame looking at the accelerating ship.
From the ship's frame, the acceleration would continue at the same rate. However, due to Lorentz contraction, the galaxy around the ship would appear to become squashed in the direction of travel, and a destination many light years away would appear to become much closer. Traveling to this destination at sub-luminal speeds would become practical for the onboard travellers. Ultimately, from the ship's frame, it would be possible to reach anywhere in the visible universe, before the ship has time to accelerate to light speed.
If you can build an engine that can constantly accelerate, without having to constantly throw fuel behind you, e.g. http://higherperspective.com/2015/03/nasa-engine.html, an astronaut can potentially travel 4 light years in less than 4 years, from their point of view, because although from Earth's reference point of view they will always be less than c, as their speed approaches c from Earth's point of view, there will be time dilation between them and Earth. If from Earth's point of view they take 4 years and a bit to travel 4 light years, assuming acceleration to very close to c very quickly, you as an astronaut will experience the same time as a lot shorter, possibly as months.
From the astronauts point of view, they can travel one light year in less than one year, if they can accelerate constantly fast enough without dying.
Of course I haven't taken into account the amount of energy that needs to be involved, except to say, if you're talking about a one-way trip, the time factor can be overcome, through technology that isn't that impossible.
If you know what's on the other side and it's possible can build a self-sustainable colony, colonising other planets is perfectly feasible from a psychological point of view given we have the technology we can accelerate close to c and decelerate from c, by achieving the time dilation effect.
If you accelerate with g=9.81 m/s^2 then you'd need
(300M/9.81) seconds which is ~30581040 seconds ~ 8495 hours ~ 354 days, so you could at least accelerate with a moderate 1g in approx. 1 year to the desired velocity.
This calculation is probably wrong because Newtonian calculations are like that (wrong) when they get close to c.
However, it deserves bonus points for
+ having exactly earth's gravity in the ship
+ travelling "up" all the time, making you feel like in a huge elevator.
However, I'm not sure whether you'd consider 354d as fast enough :)
If you see my first two links you'll see from the astronauts point of view they can accelerate indefinitely with no penalty besides chance of colliding with matter on the way. Accelerating at 1g for two years and then decelerating at 1g for two years means you will travel 3 light years in 4 years. Acceleration beyond 1g will speed this up from the astronauts point of view. At 2g it would take only 2.5ish years to reach alpha centauri from the travellers reference.
The thing is, space isn't empty, so what happens when you run into a speck of dust at a significant fraction of c? Along with our sci-fi engines we'll need sci-fi shields.
"If you can build an engine that can constantly accelerate... Of course I haven't taken into account the amount of energy that needs to be involved..."
Yes, once you throw away all the hard problems, space travel is easy.
Once you take them back into account, and seriously consider the problem as an engineering problem and not a science fiction problem, which, alas, many people have been sort of accidentally been trained to do because of the prevalence of science fiction, it starts looking really, really hard again, like, "The most plausible answer to the Fermi paradox is that star travel is impossible"-level hard.
(Which, again, isn't my opinion... I think it just means it takes a "bit" longer (you know, two or three orders of magnitude, just a trifling detail) but assuming that all possible societies in all the universe are as impatient as modern-day humans is a very strong assumption. But it isn't such a crazy argument that it can simply be dismissed... real space travel is hard.)
If you look at the reactionless drive I linked to, and if it works and can be scaled up, and in the future we can have mini nuclear or fusion power plants, all of which I see is possible, then the only problem remaining is collision on the way to the star and whether astronauts can peacefully stay on a small spacecraft for several years, knowing they are travelling in a one way time machine and people on earth will die quickly as they travel above c (technically their destination becomes closer, rather than them actually travelling this fast) from their frame of reference. I think it is not unreasonable to expect all of these problems resolved within 500 years, making space travel between stars a possibility for humanity.
Could you imagine being that lifeform that cored through the kilometres of ice to finally find an empty space with starlight shining down on you? Alone in a void, the closest celestial being is 10 light years away. Fission could power you for a long time, but rather than looking at the planet as a place fixed, the species could begin to think about where to go. As a planet. They may question whether life on a planet orbiting a sun is even possible (wouldn't it be too hot to form an ice layer?!) but where else could they head?
I bet the sky would look very different to them, too. If they did evolve eyes at all, it would probably only be in order to detect thermal radiation from other life forms on the planet; so infrared, microwave, and/or radio frequencies, but not visible light. They may even be able to plainly see the cosmic microwave background with the naked eye. It might even be blindingly bright to them.
In the different vein as the other sci-fi responses... Stanisław Lem's "Prawda" ("Truth", but probably English translation doesn't exist, I read it as "Правда" in Russian) mirrors this question with talks about how humans don't expect life at higher temperatures.
The ontological argument mated with the spaghetti monster and we got this argument.
I can envision how this planet could exist, and I can't prove it doesn't exist. Therefore it does. To make it sound scientific I'll replace "it does" with "it might"
This reminds me of a short story about Earth being flung from the solar system by a rogue star. People survive, and one family in particular survives by boiling frozen oxygen 'snow' over a fire.
Feynman's friend Ralph Leighton wrote about Felnman's long-standing desire to go there [1]. The BBC Horizon programme had an episode called "The Quest for Tannu Tuva" [2] which might be on youtube.
I just finished reading Dark Star — an entertaining scifi noir epic poem set on a planet with a dead sun. It isn't going to tell you about the practicalities of this type of thing but it is a good yarn.
It takes billions of years for life to evolve. How long before a planet floating freely across the universe gets pulled into some unstable orbit or falls onto some other (bigger) celestial body
"Atomic Rockets" has a section about "Dark Matter Planets" on their "Weird Astronomy" page. Those planets could even be heated to temperatures where liquid water can exist by exotic particles - If they are close enough to the galactic center...
"To have any chance of life – at least life like our own – a free-floating Earth would need liquid water. And to have liquid water, a planet needs to keep warm."
Would such planets have a slower rate of evolution without the radiation of the sun providing mutation, or would it just be mostly contained to the development of skin?
There's another scenario for life-supporting lonely planets. Caltech Astrophysicist David J. Stevenson has proposed a form of gas giant that can have a liquid water ocean:
62 comments
[ 4.7 ms ] story [ 43.5 ms ] threadThere would be no such thing as night and day either.
Or the planet could be teeming with water bears.
[1] https://what-if.xkcd.com/29/
> "Near the galactic center, the average distance between neighboring stars would be only 1000 AU (about a light-week). If the Sun were located within a parsec of the galactic center, there would be a million stars in our sky with apparent brightness greater than Sirius. The total starlight in the night sky would be about 200 times greater than the light of the full moon; you could easily read the newspaper at midnight, relying on starlight alone."
http://www.astronomy.ohio-state.edu/~ryden/ast162_7/notes31....
Although this would require us to 1) discover a dark planet, 2) moving at an appreciable percent of lightspeed, 3) with enough time to reach it, and 4) heading in the right direction so we could alight at a nearby solar system. If colonization sounds hard, how about those hitchhiking odds - infinitely improbable!
For comparison's sake, the only rouge planet that we know of is Mars, which moves around 24 km/s. :)
There could also be hypervelocity planets, right?
Catching up to them would be hard, though.
There could definitely be hypervelocity planets just like planets. However, the density of these drops dramatically as you increase the speed you're looking for above the "typical" speed at our galactic radius (~230 km/s), simply because they are created by chance events. I believe the density of rouge planets is supposed to be of order the average density of normal planets in the galaxy (i.e., there might be 3 times as many rouge planets, but not 100 times as many). So finding a relativistic rouge planet nearby enough to be useful has negligible probability. (They are created by close encounters with black holes, after all.)
> Catching up to them would be hard, though.
Well, if you're thinking about using them as "space ships", you need to get up to speed anyways (since the alternative is to just travel on your own).
If you could catch one, your itinerant colony would have resources at speed for interstellar travel. You'd only need to accelerate a relatively small ship. And those resources would include mass for decelerating your ship at destination. But you couldn't stop for very long, without losing your ride.
Do this mean 3,000 times less than the Suns total daily output, or 3,000 times less than the sunlight that physically hits the earth daily?
I suspect the latter, but I still find this surprising. If daily sunshine hitting the earth is so massive then let's make solar work! If we could just collect even a fraction..
This one.
> Most of Earth’s internal heat was delivered by the giant collisions that built the planet, a large portion of which remains locked inside its crust.
In 19th century, Lord Kelvin estimated the age of Earth using this method, arriving at somewhere between 20 and 400 million years[1], much shorter than 4.6 billion years currently accepted. It turns out radioactive decay keeps the Earth's inside warm for a much longer time. (I.e., assuming Kelvin's calculation was correct, without radioactivity the Earth's core would have frozen over within the first 400M years.)
[1] http://en.wikipedia.org/wiki/Age_of_the_Earth#Early_calculat...
v = (4/3) * pi * r^3
s = 4 * pi * r^2
s / v => 3/r
This makes a kind of sense in terms of heat transfer: the sun's got a whole lot more insides for radiation to get through before it can even reach the surface to escape.
EDIT: line breaks unbreak formulas.
Thanks.
>For a given shape, SA:V is inversely proportional to size.
When an object grows in size its volume grows faster than its surface area.
Instead, it should be saying:
"The solar energy flux is 3000 times greater than the surface heat flux from interior heat."
https://en.wikipedia.org/wiki/Earth%27s_energy_budget
https://en.wikipedia.org/wiki/Earth%27s_internal_heat_budget
A rogue planet in itself makes a terrible colony. And by stopping at one you about double(!) the energy/time needed to leave the solar system.
Some have decided this means star travel is impossible; I say it just limits how quickly we can do it. We could launch very large ice asteroids with nanotech unmanned fusion stations that construct lasers ("vigorous handwave about magic here") and create ourselves a series of stepping stones to a star. It would take a long time, not least of which is because we would also need to set up the "stepping stones" to stop us on the other end, too! But in theory it seems like it would "just" be a matter of time. Lots of time. But a whole star system on the other end! It's a pretty big payoff for a strapping young Kardashev II civilization.
(Note that "just send information" only works after you deliver a physical package to the other end which would be capable of receiving it and doing something with it, and even nanotech is unlikely to be able to land anywhere to begin its lengthy self-replicating process to bootup civilization on the other end if it's merrily passing through a system at 80% the speed of light relative to the local rest frame.)
If you were lucky enough to stumble on to one of these planets in the way, it would provide a pretty nice shortcut to setting up your bridge by providing you a nice, huge power source (if you can find a lot of hydrogen lying around somewhere, which is a reasonable guess) that's already more-or-less at rest in the galactic frame, allowing you to use it to relatively easily create more stages on the enormous pipeline, and allowing you the ability to relatively easily replenish the stages in the middle. (If that's even desirable... perhaps the stages can be retargeted to other stars or something once the bootstrap package is successfully delivered.)
... of course, the article's starting with "10,000 years in the future" is probably not a terrible guess about all this, as such things go. This is a guaranteed-slow process, trading time for space. Tell your great-grandchildren to ask their great-grandchildren how the initial plans to make the initial plans for all this are going, and say "hi" to the future for you. Saying "we" will do this might very well be considered to be rather impudent of me, much like Napoleon trying to claim some sort of perceptible credit for the Hoover Dam.
http://physics.stackexchange.com/questions/53587/if-a-space-...
From the ship's frame, the acceleration would continue at the same rate. However, due to Lorentz contraction, the galaxy around the ship would appear to become squashed in the direction of travel, and a destination many light years away would appear to become much closer. Traveling to this destination at sub-luminal speeds would become practical for the onboard travellers. Ultimately, from the ship's frame, it would be possible to reach anywhere in the visible universe, before the ship has time to accelerate to light speed.
http://en.wikipedia.org/wiki/Space_travel_using_constant_acc...
If you can build an engine that can constantly accelerate, without having to constantly throw fuel behind you, e.g. http://higherperspective.com/2015/03/nasa-engine.html, an astronaut can potentially travel 4 light years in less than 4 years, from their point of view, because although from Earth's reference point of view they will always be less than c, as their speed approaches c from Earth's point of view, there will be time dilation between them and Earth. If from Earth's point of view they take 4 years and a bit to travel 4 light years, assuming acceleration to very close to c very quickly, you as an astronaut will experience the same time as a lot shorter, possibly as months.
From the astronauts point of view, they can travel one light year in less than one year, if they can accelerate constantly fast enough without dying.
Of course I haven't taken into account the amount of energy that needs to be involved, except to say, if you're talking about a one-way trip, the time factor can be overcome, through technology that isn't that impossible.
If you know what's on the other side and it's possible can build a self-sustainable colony, colonising other planets is perfectly feasible from a psychological point of view given we have the technology we can accelerate close to c and decelerate from c, by achieving the time dilation effect.
This calculation is probably wrong because Newtonian calculations are like that (wrong) when they get close to c.
However, it deserves bonus points for
+ having exactly earth's gravity in the ship
+ travelling "up" all the time, making you feel like in a huge elevator.
However, I'm not sure whether you'd consider 354d as fast enough :)
Yes, once you throw away all the hard problems, space travel is easy.
Once you take them back into account, and seriously consider the problem as an engineering problem and not a science fiction problem, which, alas, many people have been sort of accidentally been trained to do because of the prevalence of science fiction, it starts looking really, really hard again, like, "The most plausible answer to the Fermi paradox is that star travel is impossible"-level hard.
(Which, again, isn't my opinion... I think it just means it takes a "bit" longer (you know, two or three orders of magnitude, just a trifling detail) but assuming that all possible societies in all the universe are as impatient as modern-day humans is a very strong assumption. But it isn't such a crazy argument that it can simply be dismissed... real space travel is hard.)
Fascinating.
http://en.wikipedia.org/wiki/Nightfall_%28Asimov_short_story...
I can envision how this planet could exist, and I can't prove it doesn't exist. Therefore it does. To make it sound scientific I'll replace "it does" with "it might"
https://en.wikipedia.org/wiki/A_Pail_of_Air
http://www.baenebooks.com/chapters/0743498747/0743498747___6...
Los Alamos, Argonne, and Tana Tuva.
Was Tana Tuva a topic of discussion during this time period? I remember Richard Feynman wrote quite a bit about it, too.
[1] http://www.amazon.co.uk/Tuva-Bust-Richard-Feynmans-Journey/d...
[2] http://sciencek.com/video/1151/horizon-1988x25-the-quest-for...
https://www.goodreads.com/book/show/18166988-dark-eden
Kind of like Flatland in that regard, I suppose, so it's not terrible.
http://www.amazon.co.uk/Dark-Star-Oliver-Langmead/dp/1907389...
http://www.projectrho.com/public_html/rocket/weirdastronomy....
Maybe, maybe not.
http://en.wikipedia.org/wiki/Hypothetical_types_of_biochemis...
http://www.nature.com/nature/journal/v400/n6739/full/400032a...
Looks like some follow-on work/speculation has happened, too:
http://www.researchgate.net/publication/237427218_Possibilit...