Near-Light Speeds Dangerous - Do Tell!
In a good example of an announcement of something which presumably all physicists, and most hard-science fiction writers and fans were already aware, in a condescencing style which implies both that they weren't and that this is some amazing new discovery, comes this article "Warp Speed Will Kill You," by Jeremy Hsu in Space.com (http://www.space.com/businesstechnology/warp-speed-kills-100308.html?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+spaceheadlines+%28SPACE.com+Headline+Feed%29&utm_content=LiveJournal):
Captain Kirk might want to avoid taking the starship Enterprise to warp speed, unless he's ready to shrug off interstellar hydrogen atoms that would deliver a lethal radiation blast to both ship and crew.
There are just two hydrogen atoms per cubic centimeter on average in space, which poses no threat to spaceships traveling at low speeds. But those same lone atoms would transform into deadly galactic space mines for a spaceship that runs into them at near-light speed, according to calculations based on Einstein's special theory of relativity.
... and first made in connection with spaceflight over half a century ago, but you wouldn't know this from reading the article.
Edelstein's personal interest in this thought experiment began 20 years ago, when his son Arthur asked him if there was friction in space. The father responded that yes, there would be hydrogen bumping off a spaceship. But he soon realized that the stray atoms of hydrogen gas would actually go right through the ship traveling close to light speed, and irradiate both crew and electronics in the process.
Well, actually that would be "friction" -- of a particularly lethal kind. If the hydrogen physically interacts with the matter of the spaceship (which by definition it would be doing if it were "irradiating" anything) the hydrogen would most definitely absorb kinetic energy from and thus slow down the spaceship. The fact that it would be also be doing much worse to the spaceship and her crew is irrelevant to that point!
Indeed, "friction" is often lethal to rapidly-moving vehicles. For an example which strongly affects present spaceflight, consider the need for re-entry shielding, which is caused by the heat of friction a hypersonic body encounters from the Earth's atmosphere. (This was what resulted in the loss of the Columbia in 2003).
Some audience members at the American Physical Society event protested that Kirk, Spock and the "Star Trek" crew would all still live because of the starship Enterprise having shields. But Edelstein noted some of the existing difficulties with creating an electromagnetic shield with any resemblance to "Star Trek" technology.
Thus, Edelstein proved himself a good physicist but a poor analyst of science-fictional technology, since Star Trek shielding most explicitly requires a physics considerably beyond our own (among other things, ST tech routinely maniuplates gravity and thus implicitly is post Unified Field Theory, possibly even post Grand Unified Theory). Not that I'm holding up Star Trek as a shining example of hard science fiction (it isn't), but Edelstein is treating it unfairly.
(Of course, warp speeds explicitly refer to faster-than-light rather than near-light speed travel. But the radiation hazards are actually worse inside the sort of warp field that we currently believe physically possible, so Edelstein's point would apply better if he better understood the science-fictional universe he was criticizing).
No doubt the Edelstein of 1810 would be explaining to us that spaceflight was impossible because not even black powder, coal, or even whale oil provides sufficient specific impulse for rocketry. Well, he would if the whole concept of "specific impulse" wasn't developed later in the 19th century than 1810 ...
The physicist concluded by suggesting that extraterrestrials might not have visited Earth because of all the problems in traveling at near-light speeds, including how to deal with deadly hydrogen space mines. But for the record, he does believe that alien life exists.
This is poor logic, since it assumes that traveling at near-light speeds is required for interstellar flight. It isn't: at a mere 10 percent of lightspeed, travel times between most stars would be around 50-100 years, which is a long time but not beyond the capability of an advanced civilization possessing some sort of suspended animation or life extension technology, or simply a purpose strong enough to make a relatively short-hop generation ship seem a viable solution.
Tsiolovsky and Goddard grasped this in the mid-1920's. Some scientists clearly haven't yet caught up to them.
In general, there are two solutions to the problem. The first is to not travel near light speed. The hazard (and fuel expenditure) grows exponentially worse, and the actual advantage in travel time from the POV of the rest of the Universe is very small, the faster one travels.
(assuming good enough life suspension and extension technology, the advantage of reducing travel time from the POV of the starship is not really all that important).
The other is to protect the spaceship against the radiation hazards of high speed flight. This can be done in a variety of ways. Assuming that one is staying under 90% of lightspeed (note: the kinds of starships we have the physics to build today would be limited to around 40-50% lightspeed maximum, and probably more like 10-25% in practice), it's perfectly practical to shield the ship's bow, by a combination of armor, magnetic fields, and lasers to disperse and ionize larger objects (such as micrometeorites). This means that a starship would be streamlined, because streamlining would reduce the amount of surface which would require strong shielding and thick armor, hence increase payload.
This assumes of course that, when we actually are ready to build starships, both our physics and our technology haven't advanced much further than even my speculations. How well would the Jordan Bassior of 1810, thinking in terms of black powder, coal and whale oil, have imagined a Saturn V or a Space Shuttle?
Captain Kirk might want to avoid taking the starship Enterprise to warp speed, unless he's ready to shrug off interstellar hydrogen atoms that would deliver a lethal radiation blast to both ship and crew.
There are just two hydrogen atoms per cubic centimeter on average in space, which poses no threat to spaceships traveling at low speeds. But those same lone atoms would transform into deadly galactic space mines for a spaceship that runs into them at near-light speed, according to calculations based on Einstein's special theory of relativity.
... and first made in connection with spaceflight over half a century ago, but you wouldn't know this from reading the article.
Edelstein's personal interest in this thought experiment began 20 years ago, when his son Arthur asked him if there was friction in space. The father responded that yes, there would be hydrogen bumping off a spaceship. But he soon realized that the stray atoms of hydrogen gas would actually go right through the ship traveling close to light speed, and irradiate both crew and electronics in the process.
Well, actually that would be "friction" -- of a particularly lethal kind. If the hydrogen physically interacts with the matter of the spaceship (which by definition it would be doing if it were "irradiating" anything) the hydrogen would most definitely absorb kinetic energy from and thus slow down the spaceship. The fact that it would be also be doing much worse to the spaceship and her crew is irrelevant to that point!
Indeed, "friction" is often lethal to rapidly-moving vehicles. For an example which strongly affects present spaceflight, consider the need for re-entry shielding, which is caused by the heat of friction a hypersonic body encounters from the Earth's atmosphere. (This was what resulted in the loss of the Columbia in 2003).
Some audience members at the American Physical Society event protested that Kirk, Spock and the "Star Trek" crew would all still live because of the starship Enterprise having shields. But Edelstein noted some of the existing difficulties with creating an electromagnetic shield with any resemblance to "Star Trek" technology.
Thus, Edelstein proved himself a good physicist but a poor analyst of science-fictional technology, since Star Trek shielding most explicitly requires a physics considerably beyond our own (among other things, ST tech routinely maniuplates gravity and thus implicitly is post Unified Field Theory, possibly even post Grand Unified Theory). Not that I'm holding up Star Trek as a shining example of hard science fiction (it isn't), but Edelstein is treating it unfairly.
(Of course, warp speeds explicitly refer to faster-than-light rather than near-light speed travel. But the radiation hazards are actually worse inside the sort of warp field that we currently believe physically possible, so Edelstein's point would apply better if he better understood the science-fictional universe he was criticizing).
No doubt the Edelstein of 1810 would be explaining to us that spaceflight was impossible because not even black powder, coal, or even whale oil provides sufficient specific impulse for rocketry. Well, he would if the whole concept of "specific impulse" wasn't developed later in the 19th century than 1810 ...
The physicist concluded by suggesting that extraterrestrials might not have visited Earth because of all the problems in traveling at near-light speeds, including how to deal with deadly hydrogen space mines. But for the record, he does believe that alien life exists.
This is poor logic, since it assumes that traveling at near-light speeds is required for interstellar flight. It isn't: at a mere 10 percent of lightspeed, travel times between most stars would be around 50-100 years, which is a long time but not beyond the capability of an advanced civilization possessing some sort of suspended animation or life extension technology, or simply a purpose strong enough to make a relatively short-hop generation ship seem a viable solution.
Tsiolovsky and Goddard grasped this in the mid-1920's. Some scientists clearly haven't yet caught up to them.
In general, there are two solutions to the problem. The first is to not travel near light speed. The hazard (and fuel expenditure) grows exponentially worse, and the actual advantage in travel time from the POV of the rest of the Universe is very small, the faster one travels.
(assuming good enough life suspension and extension technology, the advantage of reducing travel time from the POV of the starship is not really all that important).
The other is to protect the spaceship against the radiation hazards of high speed flight. This can be done in a variety of ways. Assuming that one is staying under 90% of lightspeed (note: the kinds of starships we have the physics to build today would be limited to around 40-50% lightspeed maximum, and probably more like 10-25% in practice), it's perfectly practical to shield the ship's bow, by a combination of armor, magnetic fields, and lasers to disperse and ionize larger objects (such as micrometeorites). This means that a starship would be streamlined, because streamlining would reduce the amount of surface which would require strong shielding and thick armor, hence increase payload.
This assumes of course that, when we actually are ready to build starships, both our physics and our technology haven't advanced much further than even my speculations. How well would the Jordan Bassior of 1810, thinking in terms of black powder, coal and whale oil, have imagined a Saturn V or a Space Shuttle?