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What would life be like for an Earth-like planet that orbited a star like that? What about spaceflight (e.g. from a planet to a moon) within that solar system?

What would life be like for an Earth-like planet that orbited a star like that? What about spaceflight (e.g. from a planet to a moon) within that solar system? And what would the rest of the universe look like to them?

Thorondor 5y ago
Life, including spaceflight, would be pretty much the same as it is for us. Since the entire solar system would be moving, the relative velocities of the planets and moons would be the same as in any other solar system. The rest of the universe would look quite different, though. Stars "ahead" of the solar system - in the path of its motion - would be noticeably blue-tinted and clumped together. Stars behind the system would be red-shifted. There are some great visualizations at [0]. [0] https://math.ucr.edu/home/baez/physics/Relativity/SR/Spaceship/spaceship.html https://math.ucr.edu/home/baez/physics/Relativity/SR/Spacesh...
- swayvil 5y ago
  The rest of the universe might age very quickly, relatively speaking. Stars might pass through their lifecycle in a matter of weeks. Constellations might deform over days.
  - Semiapies 5y ago
    Not at just half the speed of light.
    - MichaelApproved 5y ago
      Not even at 99.999% the speed of light. You’d need to even faster.
  - catillac 5y ago
    There is a bad-but-good hard SF book about this general subject called Tau Zero. You’d definitely need to be going much faster than 0.5c to get anything close to the effects you’re describing, but that book is a fun read if you’re interested in the subject.
    - swayvil 5y ago
      Ya I read it. It's good. But ya, you'd have to be going really #*$&#@ fast.
  - EForEndeavour 5y ago
    These numbers are wildly exaggerated, but isn't this also the wrong "direction" of relativistic time dilation? In the frame of the planet orbiting the hypervelocity star, the rest of the universe is moving at 0.5c, so the planet would measure all clocks in the rest of the universe to be running slower by a factor of 1/sqrt(1-0.5^2) = 1.15. Astronomers on this planet would measure stellar lifecycles (and every other physical process) to proceed slower, not faster.
    - deleted 5y ago
      [deleted]
    - dumpsterdiver 5y ago
      > These numbers are wildly exaggerated, but isn't this also the wrong "direction" of relativistic time dilation? In the frame of the planet orbiting the hypervelocity star, the rest of the universe is moving at 0.5c, so the planet would measure all clocks in the rest of the universe to be running slower by a factor of 1/sqrt(1-0.5^2) = 1.15. Astronomers on this planet would measure stellar lifecycles (and every other physical process) to proceed slower, not faster. You have it backwards (easy to do with such a thought experiment!). The direction of time dialation originally stated was correct. Clocks on a body moving at ludicrous speeds will be slower (to the observers present, who are able to look at those clocks) than clocks on a body not moving at ludicrous speeds. Which is to say, if you did a loop around the galaxy at light speed (hypothetical, of course) and came back to Earth and compared your clock with a terrestrial clock, your clock would be waaaay behind, and you would be younger than the people you left behind. This effect is measurable and provable even in the orbit of our own planet (albeit, at a miniscule scale). And so while your time did in fact move more slowly, the overall effect is that you time travelled into the future because everyone else was moving much faster. This of course assumes that you are able to escape intact, which is most unlikely (again, this is just a thought experiment, for argument's sake). In your defense, I know how easy it is to get turned around in such a thought experiment. Theoretically speaking from the perspective of the par-luminal traveller, it's easy to think "my clock moves slower, so am I slower?" In a way, yes, you are! Your reality moves slower relative to theirs, and for those not travelling at light speed time passes more quickly relative to your time. Objectively speaking, a human lifecycle on a very fast moving planet will equate to many, many lifecycles on a slow moving planet, if all other things are equal. And so while you are truly travelling much faster, your time moves slower, relatively speaking. Remember as a kid being told about a hypothetical traveller that enters a black hole, and at one point they become a long spaghetti string and then simply freeze in time? That's because they are moving much faster than us, and from the outside looking in they appear to be frozen. The light emitted from their mass is but an echo. They have moved far beyond the light that we see. From the inside looking out, the universe would move much faster. Again, this is an extreme example used for clarification, but it might not be as extreme as you think. Consider a solar system that gets caught within the grasp of a black hole. Initially the tidal forces tear it apart, but over eons that mass might begin acting like a normal solar system again, and harbor life once more.
  - user-the-name 5y ago
    It would not. The universe would actually age slower. However, it would also be much shorter along the axis of motion, and the stars in front of you would be much further along in their evolution than the star behind you. So you would perceive any given star to be evolving more slowly, but you would keep encountering older and older stars as you travel.
    - swayvil 5y ago
      A man goes on a 50 year voyage travelling at near lightspeed. When he returns all of his friends have aged 50 years. But he has only aged 1 year. So you see, his friends were aging 50x faster.
      - user-the-name 5y ago
        If a man goes on a 50 year voyage and returns, he will not have travelled in a straight line, like a planet zooming through space would. He would have to accelerate and change directions, which brings in the effects of general relativity which complicate things. So these two are not equivalent cases.
- knodi123 5y ago
  what about the relative velocity of the interstellar medium? does diffuse hydrogen pelting your planet at 50%C have any negative side effects?
  - NikolaeVarius 5y ago
    Life on earth seems to have done just fine.
    - knodi123 5y ago
      Earth isn't moving at 50%C relative to the interstellar medium.
Tagbert 5y ago
If the motion is generated by passing close to a binary black hole pair and being sling shot away, if the planets were still in orbit around their stars, they would likely be in very perturbed orbits. Also, the nearby passage of a black hole is probably not something that life would survive due to radiation.
MichaelApproved 5y ago
For a star that got ejected at near light speed from the galaxy, any orbiting bodies would probably be flung in other directions and no longer orbit the star. Assuming the planet miraculously hung around for the ride, after the initial acceleration, it would be no different then what we experience here on earth. Remember that everything is relative and perspective is key. A question about speed depends on who you’re asking. To us, the other star and it’s planets are traveling at near light speeds away from us. To that stars system, it’s Earth that’s traveling at near light speed away from them. Space flight would be the same and so would gravity and time. To them, nothing changes within their stars system because it’s all within the same reference frame. I guess the night sky would be the main difference for people on that planet. They’d see the galaxy they left behind as red shifted and anything they’re speeding towards as blue shifted. Since they’ve left the galaxy and was red shifted, they probably wouldn’t see as many stars with their naked eyes.
- tux1968 5y ago
  > Remember that everything is relative and perspective is key. This has always bothered me a bit, everything being relative. You can validly say that we're the ones moving at near light speed and those stars we're talking about are actually the stationary objects; there's literally no way to tell the difference. Couldn't you say the same thing about the earth and the sun? Why do we insist that we are moving around the sun, and not the other way around if everything is relative? Well I understand the reason actually, and it seems that there is good reason to believe one interpretation of relative motion is the correct one, conforming to physics.. and the other view of relative motion isn't actually what's happening in reality.
  - faanghacker 5y ago
    Because the relativity principle applies to non-accelerating motion relative to other objects. A planet orbiting the sun is accelerating toward the sun.
    - tux1968 5y ago
      > A planet orbiting the sun is accelerating toward the sun. How do we know that the sun isn't orbiting the fixed earth, and accelerating toward the earth? Everything would look _exactly_ the same to everyone. Yes, the math works out much easier and more neatly, so that is likely what is happening in reality. But from a purely relativistic framework.. you can consider any point in space the frame of reference, and all motion relative to that "fixed" point. It makes me think that relativity is actually describing a more subjective experience, rather than the objective reality where we "know" the earth orbits around the sun.
infogulch 5y ago
At half the speed of light, I'd guess that the solar system would have its heliosphere stripped by interstellar or even intergalactic medium. The heliosphere is the region around a star where the pressure of the star's solar wind is great enough to push back against the ambient gas floating around in the galaxy. For some scale, we think Voyager 1 may soon exit the heliosphere of our solar system -- a first for man made objects. As sibling comments describe, any planetary orbits that happen to survive would continue operating as usual, but if they were outside the heliosphere they would be subjected to interstellar gas traveling at half light speed in the other direction.
- pfdietz 5y ago
  Also, each proton in the interstellar medium would become a cosmic ray with energy ~120 MeV. At 1 proton/cm^3, the intensity of this radiation on the planet would be 270 kW/m^2 (more than 100x the intensity of sunlight). If this can penetrate the magnetosphere (not clear to me it could, although I bet auroras would be extreme) it would erode the atmosphere and create large amounts of radioactivity.
  - deleted 5y ago
    [deleted]
  - andromaton 5y ago
    Cue Randall Munroe
  - Retric 5y ago
    Interstellar medium has a huge range of densities from approximately 10^6 per cubic cm down to 10^-4. However, the intergalactic medium is between 10^-5 and 10^-6 in high density filaments and gets much less dense in the voids. As such in a cosmic void planets around such stars would be fine. Though it seems extremely unlike for such planets to exist.
    - infogulch 5y ago
      Even at a comparatively low density surely it's many orders of magnitude higher than how often we encounter such cosmic rays on earth. I mean if we scale down the energy output by 10^-6, 270 mW/m^2 would still be way more than any known biological system could sustain, right?

Thorondor 5y ago

Life, including spaceflight, would be pretty much the same as it is for us. Since the entire solar system would be moving, the relative velocities of the planets and moons would be the same as in any other solar system. The rest of the universe would look quite different, though. Stars "ahead" of the solar system - in the path of its motion - would be noticeably blue-tinted and clumped together. Stars behind the system would be red-shifted. There are some great visualizations at [0]. [0] https://math.ucr.edu/home/baez/physics/Relativity/SR/Spaceship/spaceship.html https://math.ucr.edu/home/baez/physics/Relativity/SR/Spacesh...

swayvil 5y ago
The rest of the universe might age very quickly, relatively speaking. Stars might pass through their lifecycle in a matter of weeks. Constellations might deform over days.
- Semiapies 5y ago
  Not at just half the speed of light.
  - MichaelApproved 5y ago
    Not even at 99.999% the speed of light. You’d need to even faster.
- catillac 5y ago
  There is a bad-but-good hard SF book about this general subject called Tau Zero. You’d definitely need to be going much faster than 0.5c to get anything close to the effects you’re describing, but that book is a fun read if you’re interested in the subject.
  - swayvil 5y ago
    Ya I read it. It's good. But ya, you'd have to be going really #*$&#@ fast.
- EForEndeavour 5y ago
  These numbers are wildly exaggerated, but isn't this also the wrong "direction" of relativistic time dilation? In the frame of the planet orbiting the hypervelocity star, the rest of the universe is moving at 0.5c, so the planet would measure all clocks in the rest of the universe to be running slower by a factor of 1/sqrt(1-0.5^2) = 1.15. Astronomers on this planet would measure stellar lifecycles (and every other physical process) to proceed slower, not faster.
  - deleted 5y ago
    [deleted]
  - dumpsterdiver 5y ago
    > These numbers are wildly exaggerated, but isn't this also the wrong "direction" of relativistic time dilation? In the frame of the planet orbiting the hypervelocity star, the rest of the universe is moving at 0.5c, so the planet would measure all clocks in the rest of the universe to be running slower by a factor of 1/sqrt(1-0.5^2) = 1.15. Astronomers on this planet would measure stellar lifecycles (and every other physical process) to proceed slower, not faster. You have it backwards (easy to do with such a thought experiment!). The direction of time dialation originally stated was correct. Clocks on a body moving at ludicrous speeds will be slower (to the observers present, who are able to look at those clocks) than clocks on a body not moving at ludicrous speeds. Which is to say, if you did a loop around the galaxy at light speed (hypothetical, of course) and came back to Earth and compared your clock with a terrestrial clock, your clock would be waaaay behind, and you would be younger than the people you left behind. This effect is measurable and provable even in the orbit of our own planet (albeit, at a miniscule scale). And so while your time did in fact move more slowly, the overall effect is that you time travelled into the future because everyone else was moving much faster. This of course assumes that you are able to escape intact, which is most unlikely (again, this is just a thought experiment, for argument's sake). In your defense, I know how easy it is to get turned around in such a thought experiment. Theoretically speaking from the perspective of the par-luminal traveller, it's easy to think "my clock moves slower, so am I slower?" In a way, yes, you are! Your reality moves slower relative to theirs, and for those not travelling at light speed time passes more quickly relative to your time. Objectively speaking, a human lifecycle on a very fast moving planet will equate to many, many lifecycles on a slow moving planet, if all other things are equal. And so while you are truly travelling much faster, your time moves slower, relatively speaking. Remember as a kid being told about a hypothetical traveller that enters a black hole, and at one point they become a long spaghetti string and then simply freeze in time? That's because they are moving much faster than us, and from the outside looking in they appear to be frozen. The light emitted from their mass is but an echo. They have moved far beyond the light that we see. From the inside looking out, the universe would move much faster. Again, this is an extreme example used for clarification, but it might not be as extreme as you think. Consider a solar system that gets caught within the grasp of a black hole. Initially the tidal forces tear it apart, but over eons that mass might begin acting like a normal solar system again, and harbor life once more.
- user-the-name 5y ago
  It would not. The universe would actually age slower. However, it would also be much shorter along the axis of motion, and the stars in front of you would be much further along in their evolution than the star behind you. So you would perceive any given star to be evolving more slowly, but you would keep encountering older and older stars as you travel.
  - swayvil 5y ago
    A man goes on a 50 year voyage travelling at near lightspeed. When he returns all of his friends have aged 50 years. But he has only aged 1 year. So you see, his friends were aging 50x faster.
    - user-the-name 5y ago
      If a man goes on a 50 year voyage and returns, he will not have travelled in a straight line, like a planet zooming through space would. He would have to accelerate and change directions, which brings in the effects of general relativity which complicate things. So these two are not equivalent cases.
knodi123 5y ago
what about the relative velocity of the interstellar medium? does diffuse hydrogen pelting your planet at 50%C have any negative side effects?
- NikolaeVarius 5y ago
  Life on earth seems to have done just fine.
  - knodi123 5y ago
    Earth isn't moving at 50%C relative to the interstellar medium.

Tagbert 5y ago

If the motion is generated by passing close to a binary black hole pair and being sling shot away, if the planets were still in orbit around their stars, they would likely be in very perturbed orbits. Also, the nearby passage of a black hole is probably not something that life would survive due to radiation.

MichaelApproved 5y ago

For a star that got ejected at near light speed from the galaxy, any orbiting bodies would probably be flung in other directions and no longer orbit the star. Assuming the planet miraculously hung around for the ride, after the initial acceleration, it would be no different then what we experience here on earth. Remember that everything is relative and perspective is key. A question about speed depends on who you’re asking. To us, the other star and it’s planets are traveling at near light speeds away from us. To that stars system, it’s Earth that’s traveling at near light speed away from them. Space flight would be the same and so would gravity and time. To them, nothing changes within their stars system because it’s all within the same reference frame. I guess the night sky would be the main difference for people on that planet. They’d see the galaxy they left behind as red shifted and anything they’re speeding towards as blue shifted. Since they’ve left the galaxy and was red shifted, they probably wouldn’t see as many stars with their naked eyes.

tux1968 5y ago
> Remember that everything is relative and perspective is key. This has always bothered me a bit, everything being relative. You can validly say that we're the ones moving at near light speed and those stars we're talking about are actually the stationary objects; there's literally no way to tell the difference. Couldn't you say the same thing about the earth and the sun? Why do we insist that we are moving around the sun, and not the other way around if everything is relative? Well I understand the reason actually, and it seems that there is good reason to believe one interpretation of relative motion is the correct one, conforming to physics.. and the other view of relative motion isn't actually what's happening in reality.
- faanghacker 5y ago
  Because the relativity principle applies to non-accelerating motion relative to other objects. A planet orbiting the sun is accelerating toward the sun.
  - tux1968 5y ago
    > A planet orbiting the sun is accelerating toward the sun. How do we know that the sun isn't orbiting the fixed earth, and accelerating toward the earth? Everything would look _exactly_ the same to everyone. Yes, the math works out much easier and more neatly, so that is likely what is happening in reality. But from a purely relativistic framework.. you can consider any point in space the frame of reference, and all motion relative to that "fixed" point. It makes me think that relativity is actually describing a more subjective experience, rather than the objective reality where we "know" the earth orbits around the sun.

infogulch 5y ago

At half the speed of light, I'd guess that the solar system would have its heliosphere stripped by interstellar or even intergalactic medium. The heliosphere is the region around a star where the pressure of the star's solar wind is great enough to push back against the ambient gas floating around in the galaxy. For some scale, we think Voyager 1 may soon exit the heliosphere of our solar system -- a first for man made objects. As sibling comments describe, any planetary orbits that happen to survive would continue operating as usual, but if they were outside the heliosphere they would be subjected to interstellar gas traveling at half light speed in the other direction.

pfdietz 5y ago
Also, each proton in the interstellar medium would become a cosmic ray with energy ~120 MeV. At 1 proton/cm^3, the intensity of this radiation on the planet would be 270 kW/m^2 (more than 100x the intensity of sunlight). If this can penetrate the magnetosphere (not clear to me it could, although I bet auroras would be extreme) it would erode the atmosphere and create large amounts of radioactivity.
- deleted 5y ago
  [deleted]
- andromaton 5y ago
  Cue Randall Munroe
- Retric 5y ago
  Interstellar medium has a huge range of densities from approximately 10^6 per cubic cm down to 10^-4. However, the intergalactic medium is between 10^-5 and 10^-6 in high density filaments and gets much less dense in the voids. As such in a cosmic void planets around such stars would be fine. Though it seems extremely unlike for such planets to exist.
  - infogulch 5y ago
    Even at a comparatively low density surely it's many orders of magnitude higher than how often we encounter such cosmic rays on earth. I mean if we scale down the energy output by 10^-6, 270 mW/m^2 would still be way more than any known biological system could sustain, right?