Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Highly relativistic spaceflight would be fatal for passengers and instruments

scirp.org

Post reply on HN
Print view View original

21–30 of 75 posts

Re: Highly relativistic spaceflight would be fatal for passengers and instruments

#21

Post by schiffern »

salimmadjd wrote: post #7

I think once we are advanced enough to figure out how to propel anything that fast or able to pack the needed energy, this part might be easy to solve. Remember per special relativity mass increases as we approach C. Also I think there will be other physiological problems while accelerating to C. It would take like 34 days at 10g acceleration to get to C. I wonder how our bodies would handle 34 days at that kind of g…

>It would take like 34 days at 10g acceleration to get to C.

So why not take 340 days at 1g?

There are many problems with high relativistic travel. This is not one of them.

Re: Highly relativistic spaceflight would be fatal for passengers and instruments

#22

Post by jessriedel »

noonespecial wrote: post #12

There's one thing I never quite got about these speculations. When you consider a ship leaving a solar system and accelerating, and the speed gained turning the "ambient hydrogen" into deadly radiation, why does it always seem to assume that hydrogen atoms are just kind of hanging out at low velocities relative to the home solar system and only turn into a problem when the bald captain says "engage"? Its a big univer…

In short, because the Milky Way disk sets a preferred rest frame. Other matter in the galaxy all rotates with approximately the same speed around the galactic center. Here are some numbers to give you intuition.

Tangential speed of the galactic disk, obtained by averaging over nearby stars: ~ 250 km/s

Speed of sun (and other nearby stars, in random directions) with respect to the galactic disk: ~ 15 km/s

Speed of Earth with respect to the Sun: 30 km/s

Speed of satellites in low-Earth orbit: 7.8 km/s

Speed of light: 300,000 km/s.

If you want more, this article discusses these speeds in the context of estimating the dark matter velocity distribution.

http://pa.brown.edu/articles/Lewin_Smith_DM_Review.pdf

It's fairly accessible as far as physics articles go.

Even if you get outside the Milky Way, the cosmic microwave background sets a preferred rest frame. I can't find the exact speed of the Milky Way in that frame, but the speed of the Earth is ~360 km/s. (This means the Milky Way's speed is somewhere between 100 and 600 km/s.)

The take-home message is that the although the laws of physics have no preferred rest frame, the actual matter out there in the universe most certainly does.

Re: Highly relativistic spaceflight would be fatal for passengers and instruments

#23

Post by noonespecial »

jessriedel wrote: post #22
noonespecial wrote: post #12

There's one thing I never quite got about these speculations. When you consider a ship leaving a solar system and accelerating, and the speed gained turning the "ambient hydrogen" into deadly radiation, why does it always seem to assume that hydrogen atoms are just kind of hanging out at low velocities relative to the home solar system and only turn into a problem when the bald captain says "engage"? Its a big univer…

In short, because the Milky Way disk sets a preferred rest frame. Other matter in the galaxy all rotates with approximately the same speed around the galactic center. Here are some numbers to give you intuition. Tangential speed of the galactic disk, obtained by averaging over nearby stars: ~ 250 km/s Speed of sun (and other nearby stars, in random directions) with respect to the galactic disk: ~ 15 km/s Speed of Ear…

Ahh. Understood. Most enlightening. Thanks for that.

Re: Highly relativistic spaceflight would be fatal for passengers and instruments

#24

Post by linuxhansl »

There's also the risk of hitting small dust particles, etc.

A quick back of the envelope calculation reveals that hitting a spec of dust that weighs just 1 ug (a millions of a gram) at 90% c produces ~36 mega joule. Not a huge amount of energy (about the energy of burning 1kg of coal), but still.

Hitting a grain of sand (10mg) at 90% c produces ~360 giga joule (energy of a small lightning)

Re: Highly relativistic spaceflight would be fatal for passengers and instruments

#25

Post by serfdomroad »

gliese1337 wrote: post #15
mbq wrote: post #8

Another point for using warp drive (=

Not necessarily. There are some interesting potential radiation issues with "warp drives" as well. For example, at the boundary of a warp bubble of the generally-Alcubierre-like variety, space is shearing / expanding such that virtual particle pairs are incapable of recombining, just like at an event horizon. That could potentially create a great deal of radiation draining energy from the warp field. Additionally, wh…

Do you have any other info/links on the problems associated with the Alcubierre?

Re: Highly relativistic spaceflight would be fatal for passengers and instruments

#26

Post by gliese1337 »

serfdomroad wrote: post #25
gliese1337 wrote: post #15

Earlier quoted context omitted.

Not necessarily. There are some interesting potential radiation issues with "warp drives" as well. For example, at the boundary of a warp bubble of the generally-Alcubierre-like variety, space is shearing / expanding such that virtual particle pairs are incapable of recombining, just like at an event horizon. That could potentially create a great deal of radiation draining energy from the warp field. Additionally, wh…

Do you have any other info/links on the problems associated with the Alcubierre?

Here is a paper on the results of interactions with external matter en-route: http://arxiv.org/abs/1202.5708

With a couple of popularizations:

http://www.theregister.co.uk/2012/03/04/killer_warp_drive/

http://www.universetoday.com/93882/warp-drives-may-come-with...

(Essentially, particles encountered en-route pile up near the boundary and are released in a large burst when you turn the thing off, which is potentially very bad for the local environment, of which you are a part.)

And here's a paper on the horizon-like properties of the warp bubble boundary: http://staff.science.nus.edu.sg/~scilooe/srp_2003/sci_paper/...

Re: Highly relativistic spaceflight would be fatal for passengers and instruments

#30

Post by _b8r0 »

I love this quote from the abstract:

  Diffuse interstellar H atoms are the ultimate cosmic space mines and
  represent a formidable obstacle to interstellar travel.
The paper[1] is an interesting read too, but of course there are other obstacles to relativistic spaceflight, such as reaching velocities capable of relativistic spaceflight.

[1] - http://www.scirp.org/journal/PaperDownload.aspx?paperID=2391...

Post reply on HN