4 ms·

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.

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.
    - yongjik 5y ago
      Well, maybe, but I think you're mixing the everyday definition of "relativity" (i.e., things are relative) with what physicists mean by "relativity" (i.e., the Theory of Special or General Relativity, both theorized by Einstein).
      - tux1968 5y ago
        > but I think you're mixing the everyday definition of "relativity" Well, yes.. because Einstein's theory beautifully makes all the math work out, explaining one interpretation of motion as the real one. But what it did at the same time was show that there is no "fixed grid" of space independent of the objects themselves. Which is what leads to my uneasy feeling of how we ever can say one interpretation is more real than another -- i admit it may just be a nonsensical perspective. As for what all physicists mean by relativity in general... I can highly recommend this old series from the National Science Foundation: https://www.youtube.com/watch?v=Y75kEf8xLxI https://www.youtube.com/watch?v=Y75kEf8xLxI
      - random314 5y ago
        Einstein's theory of relativity is exactly what you are referring to as "everyday definition of relativity ".
    - tsimionescu 5y ago
      > 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. That wouldn't work out. You can take the earth as a fixed point and describe the Sun's motion relative to it, and it would be perfectly valid, but it wouldn't look as the Sun orbiting the Earth in any kind of almost constant speed elliptical orbit, it would look like a very different kind of motion.
- random314 5y ago
  Principle of relativity applies to both accelerating and non accelerating frame of reference, unlike Newtonian physics. So yes, it is correct to say that the sun revolves around the earth or the other stars are stationary while the sun is moving.
  - tux1968 5y ago
    Thanks. Still unsettling that while both perspectives are equally valid, Newtonian physics is so much more convincing than what came before (clockwork/earth at the center of the universe). So while both relative views are equally true, the laws of physics (or at least mathematics) don't seem to hold both those views with equal esteem.
    - random314 5y ago
      In Newtonian physics the sun is the preferred frame of reference. However with the introduction of the mathematics of general relativity by einstein in 1915; we can prefer whatever reference frame we like and we get the same correct predictions. Predictions that are more accurate than Newton's.
  - CJefferson 5y ago
    No, it absolutely isn't valid to say the earth is stationary while the sun rotates around it, you end up with crazy nonsense. Technically, the earth doesn't rotate around the sun either -- they both rotate around the center of mass of the solar system, which happens to be very close the the center of the sun, so it looks like everything rotates around the sun.
    - random314 5y ago
      You only end up with nonsense in the Newtonian model. Clearly you aren't aware of what the principle of general relativity is. It is not a good idea to argue about a topic where you lack basic knowledge.
- ahmedtd 5y ago
  I was confused about this too, until a physicist friend pointed out that you can always tell which of the bodies actually did the acceleration to get up near light speed.
- revax 5y ago
  >Why do we insist that we are moving around the sun, and not the other way around if everything is relative? Try to express the trajectories relative to earth of other planets in our solar system and you will quickly understand why we use a heliocentric model.
- TeMPOraL 5y ago
  > Why do we insist that we are moving around the sun, and not the other way around if everything is relative? Because it makes the math easier - that's all. If you fix your frame of reference to the Sun, the orbits of all other bodies become almost perfectly elliptical. If you try to pin the reference frame to any other body, you end up with complicated curves. But they model the same thing[0]. So the whole thing about "Earth orbits the Sun" is that it gives same results, but is much easier to work with. Technically, for the easy math, the point you're after is the barycenter[1] of the Solar System - the center of mass, which, per Newton's First Law, can be used to center the reference frame, because it's not accelerating[3]. As it turns out, the barycenter of the Solar System spends most of the time within the volume of the Sun[2], and otherwise is very close to it. So for most calculations, you may just as well pin the reference frame to the Sun. And then, when you fix your sights at the barycenter, you'll notice the movement of celestial bodies fall out pretty much straight from joining Newton's Second Law with the Law of Universal Gravitation - m₁a₁ = Gm₁m₂/r². Your model simplifies - you now realize the movement of celestial bodies is governed by the same laws movement on Earth is, and all the complexity of geocentric model was caused by needless coordinate transformation, due to a bad choice of the reference frame. Also worth noting that historically, humans have developed the geocentric model to a very impressive level of precision - to the point that the "upstart" heliocentric model initially was worse at predicting movement of planets. It took some extra insights for the heliocentric model to beat the old ones[5] - and only then Newton came along, and people connected the effect with the cause. -- [0] - If I recall correctly, if you were to take the path of a planet in a geocentric model and do a Fourier transform on it - that mathematical operation which represents a function of time as a possibly infinite sum of sine waves - you'd notice that the path of your planet is essentially a sum of two periodic functions. One would correspond to the movement of Earth around the Sun, the other to the movement of the planet around the Sun. This would give you a strong hint that your model is needlessly complicated, and can be recreated using much simpler curves. [1] - https://en.wikipedia.org/wiki/Barycenter https://en.wikipedia.org/wiki/Barycenter [2] - https://en.wikipedia.org/wiki/Barycenter#/media/File:Solar_system_barycenter.svg https://en.wikipedia.org/wiki/Barycenter#/media/File:Solar_s... [3] - Only forces from outside the considered system could cause it to move, which we're by definition not considering when talking about our system in isolation. And besides, they add up to negligible amounts anyway. Nice thing about forces in our reality scaling like 1/r^2 or worse[4] is that they very quickly add up to nothing with distance, which makes it easy for us to treat systems as isolated in calculations, and have the results match up to reality with extreme accuracy. [4] - https://en.wikipedia.org/wiki/Inverse-square_law https://en.wikipedia.org/wiki/Inverse-square_law applies to gravity and electromagnetism; weak and strong forces drop much faster with distance. [5] - Like using ellipses instead of circles as the fundamental curve, because your competition that used circles moving on circles could just keep adding circles - they were doing a Fourier transform without knowing it, and each circle added a frequency component, increasing the accuracy of approximating the actual ellipse.
- dhsksbs 5y ago
  You can, and you’d be 100% correct. It actually annoys me that we still teach kids that the Earth revolves around the Sun and the ancients with their silly earth-centric system were wrong. Just the math is (kinda [1]) simpler, thats all. First, its a lie. And second it breeds contempt for the ancients that said and discovered many great things. I dont mind telling them that heliocentism is a great (amazing) approximation. But I really dont appreciate how from K-University previous work that has been outdone is dismissed [2] [1] the higher order terms are sill there in the heliocentric system, they're just smaller in magnitude. [2] Another example is atomism and how the physicists who rejected it are mocked in undergrad classes. Those guys were bloody titans and their models and methods are the cornerstone of modern engineering (try designing a bridge w/out continuum mechanics but using MD)
dylan604 5y ago
> Remember that everything is relative and perspective is key. A question about speed depends on who you’re asking. I wonder if this will work on trying to talk yourself out of a speeding ticket?
- midasuni 5y ago
  The richer is for travelling at an 80mph speed difference to the camera, which was travelling at the speed of the road surface.
- tsimionescu 5y ago
  There is a story (I am certain it's apocryphal, but who knows?) of someone trying to get out of a ticket for running a red light by claiming that the light of the semaphore had been blueshifted because of their speed, so they had seen it as something similar to green. The story then goes that the judge decided to calculate how fast they would have been going for red light to appear greenish because of blue shift, and then issued them the mother of all speeding tickets for going some fraction of the speed of light in a 30mph area. Edit: according to [0], you would have to be driving at 30855km/h (2237mph) to see a red semaphore as green, which comes up to ~3 millionths of c. [0] http://www.astronomy.ohio-state.edu/~ryden/ast143/ps3_soln.pdf http://www.astronomy.ohio-state.edu/~ryden/ast143/ps3_soln.p...
LorenPechtel 5y ago
I can't imagine even an inner world surviving. If a star is ejected at 150,000 km/sec and Mercury got an acceleration one part in 7,500 more it would be ejected. Is the gravity field flinging the star really that flat over that much distance??

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.
  - yongjik 5y ago
    Well, maybe, but I think you're mixing the everyday definition of "relativity" (i.e., things are relative) with what physicists mean by "relativity" (i.e., the Theory of Special or General Relativity, both theorized by Einstein).
    - tux1968 5y ago
      > but I think you're mixing the everyday definition of "relativity" Well, yes.. because Einstein's theory beautifully makes all the math work out, explaining one interpretation of motion as the real one. But what it did at the same time was show that there is no "fixed grid" of space independent of the objects themselves. Which is what leads to my uneasy feeling of how we ever can say one interpretation is more real than another -- i admit it may just be a nonsensical perspective. As for what all physicists mean by relativity in general... I can highly recommend this old series from the National Science Foundation: https://www.youtube.com/watch?v=Y75kEf8xLxI https://www.youtube.com/watch?v=Y75kEf8xLxI
    - random314 5y ago
      Einstein's theory of relativity is exactly what you are referring to as "everyday definition of relativity ".
  - tsimionescu 5y ago
    > 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. That wouldn't work out. You can take the earth as a fixed point and describe the Sun's motion relative to it, and it would be perfectly valid, but it wouldn't look as the Sun orbiting the Earth in any kind of almost constant speed elliptical orbit, it would look like a very different kind of motion.
random314 5y ago
Principle of relativity applies to both accelerating and non accelerating frame of reference, unlike Newtonian physics. So yes, it is correct to say that the sun revolves around the earth or the other stars are stationary while the sun is moving.
- tux1968 5y ago
  Thanks. Still unsettling that while both perspectives are equally valid, Newtonian physics is so much more convincing than what came before (clockwork/earth at the center of the universe). So while both relative views are equally true, the laws of physics (or at least mathematics) don't seem to hold both those views with equal esteem.
  - random314 5y ago
    In Newtonian physics the sun is the preferred frame of reference. However with the introduction of the mathematics of general relativity by einstein in 1915; we can prefer whatever reference frame we like and we get the same correct predictions. Predictions that are more accurate than Newton's.
- CJefferson 5y ago
  No, it absolutely isn't valid to say the earth is stationary while the sun rotates around it, you end up with crazy nonsense. Technically, the earth doesn't rotate around the sun either -- they both rotate around the center of mass of the solar system, which happens to be very close the the center of the sun, so it looks like everything rotates around the sun.
  - random314 5y ago
    You only end up with nonsense in the Newtonian model. Clearly you aren't aware of what the principle of general relativity is. It is not a good idea to argue about a topic where you lack basic knowledge.
ahmedtd 5y ago
I was confused about this too, until a physicist friend pointed out that you can always tell which of the bodies actually did the acceleration to get up near light speed.
revax 5y ago
>Why do we insist that we are moving around the sun, and not the other way around if everything is relative? Try to express the trajectories relative to earth of other planets in our solar system and you will quickly understand why we use a heliocentric model.
TeMPOraL 5y ago
> Why do we insist that we are moving around the sun, and not the other way around if everything is relative? Because it makes the math easier - that's all. If you fix your frame of reference to the Sun, the orbits of all other bodies become almost perfectly elliptical. If you try to pin the reference frame to any other body, you end up with complicated curves. But they model the same thing[0]. So the whole thing about "Earth orbits the Sun" is that it gives same results, but is much easier to work with. Technically, for the easy math, the point you're after is the barycenter[1] of the Solar System - the center of mass, which, per Newton's First Law, can be used to center the reference frame, because it's not accelerating[3]. As it turns out, the barycenter of the Solar System spends most of the time within the volume of the Sun[2], and otherwise is very close to it. So for most calculations, you may just as well pin the reference frame to the Sun. And then, when you fix your sights at the barycenter, you'll notice the movement of celestial bodies fall out pretty much straight from joining Newton's Second Law with the Law of Universal Gravitation - m₁a₁ = Gm₁m₂/r². Your model simplifies - you now realize the movement of celestial bodies is governed by the same laws movement on Earth is, and all the complexity of geocentric model was caused by needless coordinate transformation, due to a bad choice of the reference frame. Also worth noting that historically, humans have developed the geocentric model to a very impressive level of precision - to the point that the "upstart" heliocentric model initially was worse at predicting movement of planets. It took some extra insights for the heliocentric model to beat the old ones[5] - and only then Newton came along, and people connected the effect with the cause. -- [0] - If I recall correctly, if you were to take the path of a planet in a geocentric model and do a Fourier transform on it - that mathematical operation which represents a function of time as a possibly infinite sum of sine waves - you'd notice that the path of your planet is essentially a sum of two periodic functions. One would correspond to the movement of Earth around the Sun, the other to the movement of the planet around the Sun. This would give you a strong hint that your model is needlessly complicated, and can be recreated using much simpler curves. [1] - https://en.wikipedia.org/wiki/Barycenter https://en.wikipedia.org/wiki/Barycenter [2] - https://en.wikipedia.org/wiki/Barycenter#/media/File:Solar_system_barycenter.svg https://en.wikipedia.org/wiki/Barycenter#/media/File:Solar_s... [3] - Only forces from outside the considered system could cause it to move, which we're by definition not considering when talking about our system in isolation. And besides, they add up to negligible amounts anyway. Nice thing about forces in our reality scaling like 1/r^2 or worse[4] is that they very quickly add up to nothing with distance, which makes it easy for us to treat systems as isolated in calculations, and have the results match up to reality with extreme accuracy. [4] - https://en.wikipedia.org/wiki/Inverse-square_law https://en.wikipedia.org/wiki/Inverse-square_law applies to gravity and electromagnetism; weak and strong forces drop much faster with distance. [5] - Like using ellipses instead of circles as the fundamental curve, because your competition that used circles moving on circles could just keep adding circles - they were doing a Fourier transform without knowing it, and each circle added a frequency component, increasing the accuracy of approximating the actual ellipse.
dhsksbs 5y ago
You can, and you’d be 100% correct. It actually annoys me that we still teach kids that the Earth revolves around the Sun and the ancients with their silly earth-centric system were wrong. Just the math is (kinda [1]) simpler, thats all. First, its a lie. And second it breeds contempt for the ancients that said and discovered many great things. I dont mind telling them that heliocentism is a great (amazing) approximation. But I really dont appreciate how from K-University previous work that has been outdone is dismissed [2] [1] the higher order terms are sill there in the heliocentric system, they're just smaller in magnitude. [2] Another example is atomism and how the physicists who rejected it are mocked in undergrad classes. Those guys were bloody titans and their models and methods are the cornerstone of modern engineering (try designing a bridge w/out continuum mechanics but using MD)

dylan604 5y ago

> Remember that everything is relative and perspective is key. A question about speed depends on who you’re asking. I wonder if this will work on trying to talk yourself out of a speeding ticket?

midasuni 5y ago
The richer is for travelling at an 80mph speed difference to the camera, which was travelling at the speed of the road surface.
tsimionescu 5y ago
There is a story (I am certain it's apocryphal, but who knows?) of someone trying to get out of a ticket for running a red light by claiming that the light of the semaphore had been blueshifted because of their speed, so they had seen it as something similar to green. The story then goes that the judge decided to calculate how fast they would have been going for red light to appear greenish because of blue shift, and then issued them the mother of all speeding tickets for going some fraction of the speed of light in a 30mph area. Edit: according to [0], you would have to be driving at 30855km/h (2237mph) to see a red semaphore as green, which comes up to ~3 millionths of c. [0] http://www.astronomy.ohio-state.edu/~ryden/ast143/ps3_soln.pdf http://www.astronomy.ohio-state.edu/~ryden/ast143/ps3_soln.p...

LorenPechtel 5y ago

I can't imagine even an inner world surviving. If a star is ejected at 150,000 km/sec and Mercury got an acceleration one part in 7,500 more it would be ejected. Is the gravity field flinging the star really that flat over that much distance??