Hacker News Reader

Comment by JoeAltmaier | Hacker News Reader

The health hazards of space may be entirely treatable or preventable, with enough research. By no means in the human body any kind of barrier to exploring space!

There have been so very few space denizens, the science is in its infancy.

Space travel itself could be changed. For instance, a rocket to Mars may swing the habitat in a circle at the end of a miles-long wire to create artificial gravity. To those that claim 'acceleration is different from gravity', take your physics course again.

And people can be changed. It took a special kind of person to live at high altitude, and on an island with periodic feast-and-famine, and on a 2000 calorie rice diet, and in a crowded city, and on a submarine.

We can imagine (and often have in science fiction) a person built to crew long space missions. And we can imagine space missions designed for humans. Right now it's all in early days.

View on HN

> create artificial gravity. To those that claim 'acceleration is different from gravity', take your physics course again.

The physics course, at least if it includes General Relativity, will tell you that what the human body is used to is not gravity but acceleration. The astronauts in free fall in the ISS are fully responding to Earth's gravity; the difference between them and the rest of us stuck here on the Earth's surface is that we are feeling acceleration, because the Earth's surface is pushing upward on us, and they are not.

The potential issue with having a spaceship habitat swinging in a circle to create acceleration is the Coriolis effect; that would make it feel at least somewhat different from being on the Earth's surface, even if the magnitude of the acceleration were 1 g. That might cause something like motion sickness in some people--but then again, so does free fall. (I myself don't even like roller coasters, so I would probably be a very poor candidate for being a free-fall astronaut.)

AFAICT, the equivalence of gravitational and inertial masses is not a completely solved problem in modern physics.

Earth also rotates, and thus the Coriolis effect is present. It's not as noticeable as in a fast-rotating habitat in space, but air navigation, naval navigation, and artillery all make adjustments for it, among other factors, especially at high latitudes.

>* the equivalence of gravitational and inertial masses is not a completely solved problem in modern physics.*

I'm not sure what you mean. In GR the two are equivalent, period. There is no open issue there.

> Earth also rotates, and thus the Coriolis effect is present.

Yes, but on the scale of a human it is far, far too tiny to be detectable. So it doesn't make a difference to what humans experience on Earth, even though, as you note, there are scenarios in which it has to be taken into account.

In a space habitat swinging around to provide artificial acceleration, however, I think the Coriolis effect on a human would be large enough to be detectable by the human. At least unless you made the length of the cable it was swinging on of the same order as the radius of the Earth, i.e., thousands of kilometers, which is not likely to be practical.

In GR, the equivalence of inertial and gravitational masses is assumed, not proven in any way [1]. GR, of course, holds exceptionally well during the last 100+ years of experiments.

Indeed, in a small enough rotating habitat, jumping straight up would reveal the direction of rotation, and jumping "forward" and "backward" would have noticeably different results.

There's hoping though that the mechanisms which under zero g make the bones lose calcium, make tissues with a lot of small blood vessels swell, etc, won't be as seriously affected by the small variations introduced by the Coriolis effect as they are affected by the lack of weight and the pressure resulting from the weight. Solving 100.00% of a problem would be wonderful, but solving roughly 90% would already be highly beneficial.

[1]: https://en.wikipedia.org/wiki/Equivalence_principle#Einstein...

> In GR, the equivalence of inertial and gravitational masses is assumed

No, it's not, it's a necessary part of the way GR models gravity as spacetime curvature with the metric being the only "field" associated with gravity. You can't do that and have inertial and gravitational masses being different. I guess you could call modeling gravity as spacetime curvature with the metric being the only "field" associated with gravity an assumption, but it's an assumption that has a lot more consequences than just the equivalence of inertial and gravitational mass. So the latter is not usefully viewed as an "assumption" in GR by itself. It's one of many consequences of a much broader assumption that is the entire basis of the theory.

It is true that there are other theories of gravity that use spacetime curvature, but they all have additional fields besides the spacetime metric that are associated with gravity. And all of them known so far are ruled out by experiment, or at least the only region of their parameter spaces that are compatible with experiment make the extra fields observationally meaningless and the theories become equivalent to GR in all their predictions.

There is a gravity gradient in the centrifuge, for a 2m tall person, if the radius is only 10m, gravity gradient ranges from 20% to 100% from head to toe, meaning it's quite noticeable. But at 100m radius it's only 2%, and presumed to not be noticeable (I'm not sure if they've actually put that to the test).

https://ntrs.nasa.gov/api/citations/20070001008/downloads/20...

> a gravity gradient

More precisely an acceleration gradient, at least in the terminology I was using in my previous post. Yes, this is a good point.

So use a 1km tether. Lots of room in space.

By a lot of means is the human body a kind of barrier to exploring space, so many and with such intensity as to call into question the whole exercise. Maybe it'll all work out, but it seems unreasonable to literally dismiss the question.

All we need to do is compare the extent to which Man has explored space (and oceans and volcanoes etc.) vs. the extent that robots have been sent on our behalf, with quite resounding success, and the barriers are self-evident.

Not to mention the liability and really bad P.R. when human lives are lost in that pursuit.

I think it's unlikely. Humans (and all other life on Earth) evolved to live on Earth. I think it's very doubtful that humans can live long-term anywhere else.

It's just a technology problem.

That supposition is not altogether clear - seeds of life may have been asteroid/meteorite provided, in which case life on earth was evolved for different places entirely.

Anyway, the Cambrian explosion shows how life can fill any ecological niche from ocean-bottom sulfur vents to mountaintops, from the stratosphere to mudpots in Yellowstone.

We don't have to wait for that. Lots of science fiction about making people to fit the world. An obvious solution, and already we're gaining the tools to do it.

Sure, but once you engineer a creature capable of living in 0g, it seems likely that the biological difference will be great enough that we'll be calling it something other than "human". And it almost certainly won't be capable of living on Earth without life support.

Eyesight issues? Bone issues? Null-gravity related. Solutions are clear there, and not even hard

Radiation, that one is difficult. Water barrier? Magentic bottle? harder.

What other issues? The 'submarine' one has been largely solved, for, you know, submarine crews.

It seems you take my point. :)

And I presume you take mine - that smarter people than us will be highly motivated to solve the problem. :)

I don't agree, but past "this is a question worth taking seriously" I don't feel committed to litigating it; reasonable people can disagree!

Yes, there's clearly hurdles on the path but I think they're well worth figuring out how to clear.

There's multiple reasons why but one that stands out in my mind is the sheer difference in trajectories between a species that embraces spacefaring and comes to live on multiple worlds compared to a species that remains confined to its point of origin. In the long term, the former of those two will eventually fan out to other star systems and explore countless more modes of existence, structuring of societies, ways of expression, avenues of science, etc than the latter can ever hope to. Staying put stymies potential to an extent that's difficult to even comprehend.

In the long term, with the distances in space, the former of the two probably isn't a single species, so the scenario isn't really "a multi-planet species", it's "multiple single-planet species with a common ancestor".

You are mixing few different things here - yes AFAIK sherpas / tibetans have genes preselected to cope better with altitude, but there is absolutely 0 zilch nothing of such about 'crowded city or a submarine'.

WTF would that actually even be, submarines have cca surface pressure, maybe you meant adaptation to generally shitty soulless draining more stresful environments? Again, nothing like that out there in gene pool, city folks generally love running away to the nature as much as they can, at least those who already experienced how healing and recharging it can be and can afford it.

Yet they screen successfully for submariners and get a good crew. Their genes came from somewhere.

And every human in existence has been adapted over the last 50K years for tribal, village and city conditions. Early hominids were very different - hairier, loners, more fractious, used more calories, communicated less.

AMH (anatomically modern humans) have co-evolved with crowded conditions, to live in groups and tolerate each other without killing one another. So maybe three modifiers on that was hyperbole.

>And every human in existence has been adapted over the last 50K years

50k years is a blink in the context of evolution. You're looking exclusively at cultural adaptations in this timeframe.

Not an evolutionary biologist? Read up on it.

Humans have evolved more in the last 50K years than in the 1M preceeding that. I'm talking about biological adaptation, though you bring up a reasonable point that cultural adaptation is another tool to help bring success.

Man you are all over the place and mixing stuff that doesn't make sense.

Evolution of some trait as adaptation to environment vs selecting by test from general population with variable levels of traits are completely different things.

The other points are in same vein, no point wasting more time.

Reply on news.ycombinator.com