An iron meteorite typically has a density of 8000 tonnes per cubic meter. To fuel a craft to another galaxy, you'd need 2 spherical meteorites, each 1km wide. One made of matter, one made of anti-matter.
While this is large, we can pick up the 1km wide matter meteorite easily in space. So to travel 2 million light years to another galaxy requires us to 'only' produce a sphere 1km wide of anti-matter. This isn't really doable at the moment, but it's hardly a fantastical feat.
Hi, please see my other replies - a lot of people have asked the same thing! The answer, basically, is time dilation. Time for the people in the ship will slow down. While it will take 2 million years for people on Earth, it will only take 28 years for the people in the ship.
You could get there in 5 seconds, but the acceleration would pulp you.
Please have a look at some of my other replies to people asking the same thing.
> Is this due to relativistic effects making the ship clock run slower than an outside observers clock ?
Yes. Time dilation.
>but for the photons themselves the transfer appears to be instantaneous Yeah photons do not experience time or even distance. For them, everything is at the same place at the same time. You get zeros and infinities in the equations.
> BTW, what would the mechanism of your engine be?
Some sort of mechanism to turn mass into light.
Combining matter and antimatter would be a good candidate, although I assume we can do so with 100% efficiency. We can currently reach 50% I think, which is probably good enough.
> How would we account for conservation of momentum?
The light carries the momentum. For momentum to balance, you have to have that:
But you also don't want to carry lots of fuel. So you want the fuel_mass to be very very small and the fuel_velocity to be very very large. The natural candidate is to thus emit light itself. (In this context, light has (relativistic) mass)
As you accelerate, you 'just' get closer and closer to the speed of light and time slows down for the people in the spaceship. This is what this is all based on - that the constant acceleration means that time slows down more and more for the people on the space ship.
At the peak speed for travelling to another galaxy, say, they will still only be travelling close to the speed of light, but a million of years will pass on earth for something like a year or two for the people in the rocket.
> Wouldn't there also be the issue of navigation to avoid obstacles?
Yes, a huge issue. After accelerating for just one year, the heat that exists in space (microwave background cosmic radiation) will be hitting the spacecraft will be hotter than any known material could withstand. We would have to have some sort of 'light shield' that we have not yet invented or something.
You're forgetting about time dilation, just like everyone else that has replied to my comment asking about this. Time slows down for the people in the space ship (or viewed another way, the distance is length contracted)
Pretty much just the distance travelled, times 2, in years.
So going to Andromeda galaxy and back again (2,000,000 light years) would take 56 years according to the person in the spaceship, and he would come back to a world that has aged 4 million years.
Time dilation and distance contraction. This are special relativity effects.
For the people on earth, the ship takes 4 million years to travel 4 million light years at close to the speed of light. But for people in the rocket, it can be a very short amount of time.
> you didn't account at all for relativistic effects at all.
It fully takes into account SR effects.
> A big question is how come you can travel faster than light It doesn't. All times as for the people in the spaceship, as I stated. The reason it takes less time is because of time dilation.
> when you get to Vega everyone who sent you will be long dead. Indeed.
If you accelerate at 9.8m/s^2 for half the journey and -9.8m/s^2 for the second half of the journey (so that it's just like earth's gravity) then you would arrive at the planet after:
1.94 arccosh(n/1.94 + 1) years
For n=10.5 light years, this gives 4.9 years.
For other values of distance: 4.3 ly nearest star 3.6 years 27 ly Vega 6.6 years 30,000 ly Center of our galaxy 20 years 2,000,000 ly Andromeda galaxy 28 years
(For distances bigger than about a thousand million light years, the formulas given here is inadequate because the universe is expanding. General Relativity would have to be used to work out those cases.)
So for someone in the rocket, they could arrive at the planet in 4.9 years.
If you had an 100% efficient engine (using anti-matter/matter), the fuel required would be:
d Stopping at: M 4.3 ly Nearest star 38 kg 27 ly Vega 886 kg 30,000 ly Center of our galaxy 955,000 tonnes 2,000,000 ly Andromeda galaxy 4.2 thousand million tonnes
I find it fascinating that within a human lifetime (for the people in the rocket) we could travel to another galaxy.
> It might being worked on, but the current state is that it isn't there and it isn't available right now.
You're honestly saying that Xorg doesn't support DRI? Really?
> Where did I say I talked to the Xorg team?
You state on your 'People in the opensource community claim that there is no real performance penalty because of certain accelerated features, despite the fact 3D applications are just slowed down because they have to use non/semi-accelerated indirect rendering (depends on the driver).'
> Where is it? I don't see it in Ubuntu intrepid. Because it's not done. If every company did it NVidia's way, we'd a have reimplementation of a manager manager for every driver. Are you really arguing that this is the best solution?
So basically, NVidia wrote their own memory manager rather than working with the community. Compared to Intel which is working with the to write a memory manager (TTM) which will benefit everyone.
Of course X does direct rendering. It's called Direct Rendering Interface - DRI. And the new improved DRI2 being worked on now.
His other argument is that Xorg will never be able to have a unified memory manager... which is exactly what TTM and its successor GEM do.
And noone in the Xorg team claims that indirect rendering is as fast as direct rendering.
Companies like NVidia just replace chunks of Xorg without contributing anything back. Whereas its companies like Intel that actually contribute to improving X for everything - pushing a unified memory manager (TTM/GEM) into the kernel etc.
> A clean new implementation of x11 would probably benefit us a lot more than another Y windows, Wayward, Aqua etc
Not really. KDrive was a clean implementation of X which had a few nice improvements. Those improvements were incorporated into Xorg and now there's just no advantage to using kdrive over xorg.
I see no evidence that Xorg would benefit from a rewrite, compared to putting that energy into working on Xorg.
Slashdot Mirror
Thanks for the reply. I was thinking about your previous reply last night - I didn't mean to reply to you in such a terse form.
I will reread what you've written and think about it all some more - thank you.
Do you have any suggestions on what to read for this? Thanks
Which is why I specifically stated that my equations will not hold for distances larger than a galaxy, where you require GR.
An iron meteorite typically has a density of 8000 tonnes per cubic meter. To fuel a craft to another galaxy, you'd need 2 spherical meteorites, each 1km wide. One made of matter, one made of anti-matter.
While this is large, we can pick up the 1km wide matter meteorite easily in space. So to travel 2 million light years to another galaxy requires us to 'only' produce a sphere 1km wide of anti-matter. This isn't really doable at the moment, but it's hardly a fantastical feat.
Hi, please see my other replies - a lot of people have asked the same thing! The answer, basically, is time dilation. Time for the people in the ship will slow down. While it will take 2 million years for people on Earth, it will only take 28 years for the people in the ship.
You could get there in 5 seconds, but the acceleration would pulp you.
Please have a look at some of my other replies to people asking the same thing.
> Is this due to relativistic effects making the ship clock run slower than an outside observers clock ?
Yes. Time dilation.
>but for the photons themselves the transfer appears to be instantaneous
Yeah photons do not experience time or even distance. For them, everything is at the same place at the same time. You get zeros and infinities in the equations.
> Don't your calculations require the assumption of Newtonian physics?
No, this is an integration of the special relativity lorentz transformation.
> BTW, what would the mechanism of your engine be?
Some sort of mechanism to turn mass into light.
Combining matter and antimatter would be a good candidate, although I assume we can do so with 100% efficiency. We can currently reach 50% I think, which is probably good enough.
> How would we account for conservation of momentum?
The light carries the momentum.
For momentum to balance, you have to have that:
fuel_mass * fuel_velocity = ship_mass * ship_velocity
But you also don't want to carry lots of fuel. So you want the fuel_mass to be very very small and the fuel_velocity to be very very large. The natural candidate is to thus emit light itself. (In this context, light has (relativistic) mass)
As you accelerate, you 'just' get closer and closer to the speed of light and time slows down for the people in the spaceship. This is what this is all based on - that the constant acceleration means that time slows down more and more for the people on the space ship.
At the peak speed for travelling to another galaxy, say, they will still only be travelling close to the speed of light, but a million of years will pass on earth for something like a year or two for the people in the rocket.
> Wouldn't there also be the issue of navigation to avoid obstacles?
Yes, a huge issue. After accelerating for just one year, the heat that exists in space (microwave background cosmic radiation) will be hitting the spacecraft will be hotter than any known material could withstand.
We would have to have some sort of 'light shield' that we have not yet invented or something.
You're forgetting about time dilation, just like everyone else that has replied to my comment asking about this. Time slows down for the people in the space ship (or viewed another way, the distance is length contracted)
Pretty much just the distance travelled, times 2, in years.
So going to Andromeda galaxy and back again (2,000,000 light years) would take 56 years according to the person in the spaceship, and he would come back to a world that has aged 4 million years.
Pretty mind blowing.
Right, time dilation and length contraction.
> The first half is correct, but the second half is wrong.
No it's not :P
> so the fuel you need is proportional to travel time in the traveller's timeframe, not the distance traveled.
The formula I gave isn't proportional to the distance traveled. it's a hyperbolic relation to distance.
> This is of course assuming mass_ship >> mass_fuel, but I think you assumed that as well.
The opposite - I assume mass_fuel >> mass_ship
> You left out where the energy to sustain 1 gee is going to come from
I gave the calculations for the energy/mass required to sustain 1g.
> Also with \gamma>>50 the blue shifted microwave background is not looking so nice.....
Shields :-)
Time dilation and distance contraction. This are special relativity effects.
For the people on earth, the ship takes 4 million years to travel 4 million light years at close to the speed of light. But for people in the rocket, it can be a very short amount of time.
> you didn't account at all for relativistic effects at all.
It fully takes into account SR effects.
> A big question is how come you can travel faster than light
It doesn't. All times as for the people in the spaceship, as I stated. The reason it takes less time is because of time dilation.
> when you get to Vega everyone who sent you will be long dead.
Indeed.
I did the calculations for an earlier post:
If you accelerate at 9.8m/s^2 for half the journey and -9.8m/s^2 for the second half of the journey (so that it's just like earth's gravity) then you would arrive at the planet after:
1.94 arccosh(n/1.94 + 1) years
For n=10.5 light years, this gives 4.9 years.
For other values of distance:
4.3 ly nearest star 3.6 years
27 ly Vega 6.6 years
30,000 ly Center of our galaxy 20 years
2,000,000 ly Andromeda galaxy 28 years
(For distances bigger than about a thousand million light years, the formulas given here is inadequate because the universe is expanding. General Relativity would have to be used to work out those cases.)
So for someone in the rocket, they could arrive at the planet in 4.9 years.
If you had an 100% efficient engine (using anti-matter/matter), the fuel required would be:
d Stopping at: M
4.3 ly Nearest star 38 kg
27 ly Vega 886 kg
30,000 ly Center of our galaxy 955,000 tonnes
2,000,000 ly Andromeda galaxy 4.2 thousand million tonnes
I find it fascinating that within a human lifetime (for the people in the rocket) we could travel to another galaxy.
(I'm a theoretical particle physicist)
You can filter out salt with a membrane system?
When you have an A4 book that you want to display on an A5 kindle? That's the most obvious example where you want to reprocess
> It might being worked on, but the current state is that it isn't there and it isn't available right now.
You're honestly saying that Xorg doesn't support DRI? Really?
> Where did I say I talked to the Xorg team?
You state on your 'People in the opensource community claim that there is no real performance penalty because of certain accelerated features, despite the fact 3D applications are just slowed down because they have to use non/semi-accelerated indirect rendering (depends on the driver).'
> Where is it? I don't see it in Ubuntu intrepid.
Because it's not done. If every company did it NVidia's way, we'd a have reimplementation of a manager manager for every driver. Are you really arguing that this is the best solution?
So basically, NVidia wrote their own memory manager rather than working with the community. Compared to Intel which is working with the to write a memory manager (TTM) which will benefit everyone.
And somehow NVidia is better than Intel? lol
Ash-foxes blog post is close to being a troll.
Of course X does direct rendering. It's called Direct Rendering Interface - DRI. And the new improved DRI2 being worked on now.
His other argument is that Xorg will never be able to have a unified memory manager... which is exactly what TTM and its successor GEM do.
And noone in the Xorg team claims that indirect rendering is as fast as direct rendering.
Companies like NVidia just replace chunks of Xorg without contributing anything back. Whereas its companies like Intel that actually contribute to improving X for everything - pushing a unified memory manager (TTM/GEM) into the kernel etc.
> A clean new implementation of x11 would probably benefit us a lot more than another Y windows, Wayward, Aqua etc
Not really. KDrive was a clean implementation of X which had a few nice improvements. Those improvements were incorporated into Xorg and now there's just no advantage to using kdrive over xorg.
I see no evidence that Xorg would benefit from a rewrite, compared to putting that energy into working on Xorg.
You can play nethack as a tourist and complete it without killing a single creature.
You can even play as a vegetarian or a vegan.
It's a bug in your understand. Time slows down when you go faster.
Plus 'lifetime' means half-life.
"lifetime" in the context of particles is always understood to mean "half life". It's just the terminology of the field.
> Secondly, time may slow down for muons but the "1cm in 20ps" was quoted for the unknown particle
Yeah typo :) I was using muons as an example in another post, because muon decays were the first major pieces of evidence for time dilation.