How would gravity on another world influence human lifespan?

[Tazerfish]

This is just a wild-ass guess so what difference does the predicate assumption make?

I didn't pull the numbers completely out of my butt.
From looking at causes of mortality, I concluded that two thirds of causes will likely not be influenced by higher gravity. Why would asthma or cancer increase for example?

Then I looked at relationships between heart disease and height, under the assumption that height serves as a weak analogue of higher gravity, and found that tall people actually have less cardiovascular disease.
So pumping blood across a larger pressure difference between head and feet can't be that big of a deal.
Further credence is led to this idea when considering giraffe's or elephants Cardiovascular system or even the giant dinosaurs of old. We're nowhere near a limit on size/blood pressure.

And for joint damage and movement, we need only look to obese people on earth. When your BMI is 34 then you're already in 1.4 times gravity when compared to a person with a BMI of 24. Which is to say nothing of the added risk for Diabetes, acid reflux, problems of the liver, gallbladder, or even cancer.
I'd assume that with a healthy weight in g higher gravity, you're even avoiding some of the (metabolic) issues of obesity.


You ask why I even make a distinction between the two scenarios.
Well, one corresponds to a mass increase of 37% (11% more gravity), the other to a gravity increase of 37%.
I'm unsure, which one the OP was going for.

The first one is clearly marginal. Weighing 10% more is well within the population variation. Some are taller, some are shorter. Muscles, including your heart, can easily get 10% stronger.
We'd be well within our abilities to adap to this.

37% is a different story. This is now much more comparable to being obese. 37% is also an adaptation that isn't trivial, whether it's in strength or endurance.
We're reaching the limits of adaptability, especially in old age. You'd need a wheelchair or walking aids sooner. Bone fractures will also likely become more common. It's basically like falling 37% further.


The numbers clearly make a difference.
For an extreme example 4g isn't survivable long term.
You have fighter jet pilots wearing g suits and doing weird breathing exercises so as not to pass out, and that's not saying anything about walking.

Even 2g would be a struggle. Large fractions of the population struggle to leg press twice their weight. Suddenly you're like an old man at age 50, unable to get up after a fall.

I'm pretty happy with my guesstimate.
Now, I can't conclusively say that people won't drop dead before 60 on that 1.37g world or actually, miraculously do better.
But I'd be pretty surprised!

 

[hutchphd]

I will stipulate to "wild-ass guesstimate" if you prefer (see revision). There was certainly an attempt made.

 

[Hornbein]

Oops again. If the planet density doesn't change, then to get 37% increase in gravity you need 150% more mass. That means 2.5 more mass.

 

[gmax137]

To cool down it could be further from the Sun. Then the seasons would be milder and the years longer.

The seasonal variation is due to the tilt of the axis, something not discussed in this thread, afaik.

 

[DaveC426913]

The seasonal variation is due to the tilt of the axis, something not discussed in this thread, afaik.

I think it makes more sense if you take Horn's comments in their context: he's talking about absolute temperature of the planet cooling down. Moving farther from the planets would accomplish that.

The reference to seasons being "milder" I did not interpret as being "summers: cooler, winters: warmer", I interpreted it to mean "year-round temperatures will be more liveable and less skin-melting".

 

[Tazerfish]

I will stipulate to "wild-ass guesstimate" if you prefer (see revision). There was certainly an attempt made.

Yeah, and if you think about it, it was one of the few comments that may have actually been useful to the OP!
Though honestly, they seem to have left.


They're an author. Saying "nobody knows", while it's true and important to know, is not very useful for someone writing a book.
Especially because it doesn't mean "we have no clue at all". We know pretty damn well that life expectancy won't suddenly be 100+, and I find it exceedingly unlikely that humans would routinely die off under the age of 40, even at 1.4g.
There's different levels of "don't know".

Jrmichler had an interesting approach of reverse-applying zero-g effects, though it's unclear how that might affect life expectancy.

Then there was an interesting point about quicker falls and faster necessary reaction, where folks realized, it's not *that* different. Again, it's not terribly relevant to life expectancy.

No one made a quantitative estimate.
Now, you may argue it's pointless, but I don't think so.

There's a lot of stuff that's hard to predict!
Will stock prices go up or down, who will win the presidency and which teams will win sports cups?
On all of these things, people make predictions; on all of these things, people bet money.
Some of them are clearly better than others at it.
Plus, the equilibrium-price of these "prediction markets" is a pretty good agglomerate of expert opinion.
For the US Presidency, they typically outperform any single expert.

Just because something is deep within the fog of war, doesn't mean there aren't better or worse answers to a question.
Plus, munching a bunch of answers together usually improves the result.

I'd be willing to bet that humans that would have a 80 year lifespan will still die between 65 and 85 (at one to one odds).
Which, to be frank, feels like a pretty conservative estimate, I could either take a steeper bet or narrow the age range down way further.
When writing a book, I'd go with 0-5 years less life expectancy when compared to their equivalent 1g counterparts.

Hell, someone even agreed that medical progress or dutifully applying current health guidelines would result in a larger life expectancy effect than 10% more gravity. I'd guess it's even stronger than 40% more gravity, but I might be way off.
Both *agreement* and *disagreement* are then important in further shaping the best "group guess".

It's okay if you don't agree with this epistemological approach, but I wanted to put it out there. I don't think it was all pointless.
I'm pretty sure, if humanity threw a ton of resources at this, we could give a decent guess, even without some long term experiment with some folks living in a centrifuge at different gravity.

I'll get off my soapbox now.

 

[hutchphd]

I'll get off my soapbox now.

What you say may be true but

I wanted to put it out there. I don't think it was all pointless.

This is true for nearly all practitioners.
I do not accuse you of ill intent, but unless your purported guesstimate carries a reasoned affiliated uncertainty, it should not be considered in any way quantitative. Attempting to cloak it in the scientific raiments merely sullies the wrapper: I take exception, and stand by my previous characterization.

 

[Vanadium 50]

Saying "nobody knows", while it's true and important to know, is not very useful for somshoone writing a book.

So what false answer should we provide if we want to be helpful?

 

[Tazerfish]

Is it really somehow more noble to say, "Whereof one cannot speak (scientifically), thereof one must be silent."?
It's ultimately a philosophical question.

I feel that an answer providing an age range and some of the reasoning which led me to it is useful.
Moreover, a specific quantitative answer is more easily testable. Of course, it's a huge mistake to treat these numbers anything like those produced by statistical analysis, but so long as people are aware of how they came to be, I think it's useful.

When looking back on a concrete (quantitative) guess, it's much harder to worm your way out of a mistake; instead, you are forced to reconsider your belief when a prediction doesn't come to pass.

Some guesses are really valuable, even if they're not backed up by formal scientific analysis.
Researchers can guess how likely a study in their field will replicate; appraisers can guess whether a piece of art is real or a forgery; medical professionals can guess at a diagnosis or what the medical outlook of a patient will be.

Yes, these guesses are often surprisingly bad when evaluated, and statistical algorithms usually outperform experts, where they exist.
Despite all this, they're still better than chance (usually)

I'd only accept this criticism if you feel that within the vast web of factors affecting human lifespans, we are in way over our head.
Like a random person looking at an MRI image, supposed to make a diagnosis while not even able to tell apart the different organs.

It's not like any one of us is an expert on human longevity and it's dependence on environmental factors...

IMO, guesses are valuable.
Between complete ignorance and firmly established science, there exists a middle ground.
A middle ground we traverse constantly.
From investment to parenting, you never have all the data. You never know the future for certain.
But you can guess!
Often, that's the only way to get anywhere.

But we're turning in circles, having left science behind, straying into philosophy.
You know my position, I sort of know yours.
It's probably time to leave it at that.

 

[Nik_2213]

Came late to thread...
Assuming settlers get past the first generations by wearing pressure-sox routinely, spending a lot of time pool-resting and swimming for relief via buoyancy...:
IMHO:
Some may go stocky, like power-lifters
Some may go slight, like dainty Asians.
Scant few will be tall...

Uh, what's the planet's day length ? If really short, equatorial regions will feel a significantly lower gravity...

 

[Nik_2213]

Another consideration: 'Personal Protective Equipment' ??
Hip / elbow / head protection may be popular...

Disclosure: I wear discreet hip-protection pads, as my age etc leaves me vulnerable to a disastrous stumble or slip. Our now-elderly cats leave fewer toys about, but still leg-weave from time to time. Out-doors, cash-strapped local authority is far, far behind on repairs to all but the worst 'wonky walk-ways'.
'In Extremis', knowing 'leading' hip is probably safe lets you concentrate on rest of 'break-fall' slap-down...

 

[Laroxe]

Well, this seems to directly address the question while (helpfully?) adding the complexity of hormonal control.

https://pmc.ncbi.nlm.nih.gov/articl...t,some physiological and behavioral variables.