Why can't we go to the center of the galaxy?

[MonstersFromTheId]

This is an incredibly interesting conversation. But a few q's from a complete neophyte here if you don't mind.
Three actually.
1) Even in REALLY deep DEEP interstellar space, the "vacuum" of space is no "vacuum" right? I mean there are ALWAYS at least SOME stray molecules floating around in every cubic foot of space right?
So even if the "vacuum" of space looks like a "vacuum" at mach 18, at .1c wouldn't the "vacuum" of space start to look a lot more like a kind of soup?
2) Wouldn't hitting just random molecules along the way essentially irradiate the living piss out of any potential crew?
3) What would happen if you tried to tear ass through the Sagittarius Nebula at something like .1c? Wouldn't that wind up being a bit like diving head first into a shotgun blast?

 

[selfAdjoint]

You are describing the "relativistic ramjet" idea. This was popular a couple of decades ago but detailed studies showed that the drag would exceed the reaction generation. So we're back to carrying your reaction mass along.

Of course there are "new physics" (i.e. crank) proposals all the time. "Vacuum propellers" or coupling to the zero point energy was one. And there are always the weird solutions of Einstein's field equations, like wormholes and the Alcubiere warp drive.

 

[Nereid]

This is an incredibly interesting conversation. But a few q's from a complete neophyte here if you don't mind.
Three actually.
1) Even in REALLY deep DEEP interstellar space, the "vacuum" of space is no "vacuum" right? I mean there are ALWAYS at least SOME stray molecules floating around in every cubic foot of space right?
So even if the "vacuum" of space looks like a "vacuum" at mach 18, at .1c wouldn't the "vacuum" of space start to look a lot more like a kind of soup?
2) Wouldn't hitting just random molecules along the way essentially irradiate the living piss out of any potential crew?
3) What would happen if you tried to tear ass through the Sagittarius Nebula at something like .1c? Wouldn't that wind up being a bit like diving head first into a shotgun blast?

The ISM is (mostly) a plasma, so, being charged, there is a way - in principle! - to reduce the multiple hazards of colliding with lots of ions and electrons (really intense and well-designed magnetic fields). However, this doesn't work so well for neutral particles.

I'm sure all readers realize that denizens of the ISS, Shuttle, etc are doing a real-life experiment with the effects of impacts with relativistic particles ... right now. Cosmic rays are comprised of both neutral (few) and charged particles (mostly protons), and the Sun emits copious quantities of them too (though not really 'relativistic'). We here on the surface of the Earth are being hit in the head by ~6 CRs per second (IIRC); effect? And that's with a few hundred kms of air.

I suspect the infrequent collision with micron-sized ISM dust grains would be far more hazardous than even the ISM neutral gas at 0.1c

Anyone like to suggest a back-of-the-envelope calculation? (It's not all that difficult)

 

[russ_watters]

No one addressed this one...

12 years to travel to the centre which is thousands of light years away? are you sure.. if so...
that means as far as the travelers are concerned, they are moving towards the centre faster than light. It's a funny bit of SR. first you get your head round the idea that nothing can travel faster than light so you'd think it'd take thousands of years even from the travels point of view, then you realize space contraction effect cancels it out so things can appear to travel faster than light, in this case, the centre.

Does this case work for any old particle flying towards the earth?

Not quite. The length contraction cancels out time dilation in such a that they would not percieve themselves travleing faster than C. They wouldn't travel 33,000 ly in 20 years, but rather they'd travel 17 ly (guess) in 20 years (according to them), never exceeding C.

 

[billy_boy_999]

DOc Al - okay, i think i understand the 'exhaust velocity' idea a bit better, but i don't see how the exhaust velocity would limit accrued speed, it simply limits the gradient of acceleration...

nereid - very interesting, could we really design a magnetic 'shield' to neutralize charged particles? what about the dust grains? would there be any (theoretical) way to use the energy and rest mass of these dust grains to our advantage in the same way that we can funnel interstellar hydrogen into our (again, theoretical) fusion drive?

russ - this is a very important point, length contraction and time dilation adjust themselves in such a way that no one can ever measure his speed to be greater than c...but i think, too often, the popular impression is one that ignores length contraction, and time dilation, and insists on using simple earth-based measurements of distance to prohibit travel to the rest of the galaxy...within the bounds of relativity there is no limit to where you can travel in a certain amount of time...

 

[franznietzsche]

the "speed of light" relative to what? to earth? relative to earth, yes it would take a very long time but remember time dilation and the principle of relativity...as far as the crew of the spaceship is concerned there is no speed limit...

the time it would take to get to the center of the galaxy is only limited by the gradient of acceleration...the gradient of acceleration is only limited by the thrust of the rockets and the mass of the ship, if we can make nuclear thrust technology very efficient i think the journey is a perfectly plausible one...

Slightly erroenous, the speed of light is constant for all observers. The travelers are still limited to the speed of light, the velocity they would measure for the objects moving apst them. But because of length contraction they would say they were traveling at the speed of light, but convering a shorter distance. This is what causes the shorter travel time by the moving clocks.

 

[energia]

let's just face the fact that no existing propulsion system will ever result in interstellar travel

it will take breakthrough physics to accomplish that

and breakthrough physics discoveries are few and far between

the current prospects of joining the federation of planets are dismal

so just get used to watching perpetual space shuttle launches for the forseeable future - as far as propulsion technology is concerned - there has been no progress since the 1960's

the last moon landing (11 December 1972) tolled the end of manned planetary exploration for the 20th century (nearly 32 years ago!) who knows how long it will be before the next moon landing - 32 more years maybe? (most likely with 60's technology) and manned missions to Mars are just a dream until the next generation of propulsion becomes reality

since the cold war ended - the days of cowboy rocketscience are over
(those were the days) I would guess that interplanetary manned missions (within this solar system) may happen by the end of the 21st or 22nd century

missions to the nearest stars?
possibly 300 to 1000 years into the future (maybe)

galactic missions?
possibly never
current physics notwithstanding

 

[setAI]

it seems to me that it would be rather silly to send huge primates and chunks of plastic/steel- if I were considering such a long journey- I think that it would be more prudent to encode the crew/environment/ and a copy of all human knowledge into some quantum-scale computing system- you would transmit or project the ship to it's destination- I would be quite dissapointed in the engineers if the vessel were big enough to be visable by the human eye-



BTW- hello I'm new! (^_^)- I'm not a physicist- I'm a computermusic composer and incorporate some AI/AL/cog sci research into my art- [physics was my first declared major-I was going to go into cosmology but this was the late 80's and my love of the human brain and AI [and sythesizers] won me over so I ended up swept up into the great attractor that was the Santa Fe Inst in the early 90's- when the party was over I settled down into life as a self-styled crackpot/ chaos-shaman/ artist/ polymath/nutter [with a day-job]- thanks to excessive research into psychotropics and too much free time/money (as most of my collegues at SFI did- I think) ]

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