The sinuses alone are what, like 2-3% of the volume alone? So being a bit stuffed up one day would probably put you over the threshold.
I dunno, my total body mass easily varies by >1% day-to-day and even more across a few days, despite me weighing myself under basically exactly the same conditions each time. As best I can tell most of this variation is from changes in water retention. Although the brain is probably less affected than other organs, plenty of the head’s total volume is just skin and muscle, which I’d expect to be as affected as anything.
If an average head is 4 kg, 1% of that is just 40 grams. And really we should be thinking of deviations; if we’re just 20 grams “low” on one day, and 20 grams “high” on the next, that’s still 1%.
For the record, this is all just personal speculation based on a limited amount of personal knowledge. Contrary to what some have claimed, I do not in fact have a personal collection of human heads in jars that I can draw inferences from.
ETA: It would not shock me if the trimmings from a haircut weighed >40 g (I have very thick hair).
Consider also the possibility that I’m enraged due to someone trying to cut off my head in order to weigh it. My blood vessels will have dilated significantly, possibly by >10% in average cross-sectional area. If my head typically contains 500 ml of blood, it will now contain 550 ml (taken from less important parts of my body), which is also enough to cause 1% variation.
One day we’ll be a Kardashev Type II civilization and Coca-Cola will use gravitational wave manipulators to engrave their logo into the Sun (even though it’s actually better suited to Pepsi).
Okay this strays farther afield but where better to nerd out on a question like this?
Item the first. Accuracy of volumetric MRI. Different software using the same machines and same imaging protocols will vary by 5 to 10%.
The second. Day to day variation. OTOH any true day to day is still the real weight of the head at that moment. But no, head mass should change little compared to the rest of the body. Cerebral blood flow does shift in various regions but total blood volume in the brain just has no space to increase. It is a confined space and increasing pressure … is bad. The sinuses don’t typically go from all air filled to socked in with fluid and pus. Maybe day to day a little mucosal thickening? But that is insignificant on scale. You are correct that muscles and various organs can change volume day to day, just with how much glycogen and obligate water is there, (skin not much but can vasodilate and increase blood volume a little), but the head actually has little of its volume or mass as muscle.
Uh, what? A Type 4 controls all energy in the known universe. What the heck is a Type 6+?
Granted, I am assuming some future tech allows manipulation of gravity using energies a bit less than black hole scale. Or at least using stable micro black holes. Either way, something on the order of the sun’s energy output, rather than the galaxy or more.
D. D. Harriman is a private businessman who’s driving the first manned mission to the Moon, and is securing funding wherever he can. He ends up selling rights to advertising on the Moon’s surface, visible from Earth, to a soft drink company who has no intention of using those rights, by hinting that 6+ (a fictitious rival soft drink brand) would buy them instead.
Yeah, like I said originally, no way you’re actually getting within 1% with an MRI. Though I see from the paper that they had the greatest variation when measuring specific brain structures. Well, that’s not too surprising. The “whole brain” volume was <2% different.
But we’re talking about only 1%–again, on the order of 40 grams. A Google search tells me that the surface area of the sinuses and nose are 100-200 cm^2. So you could add 15-30 grams just from a 1 mm difference.
Ahh! Perhaps suprirsingly, I’ve never read that particular Heinlein (though I’m aware of the advertising angle). I keep meaning to get the full collection and go through it.
Total volume of the sinuses is roughly 20 to 25 ml. Go from all air filled to all fluid filled, complete opacification, which can happen over the course of a week with the onset of severe pansinusitis, can gain up to 25g. Limit case.
1 mm may sound like a little but in the spaces it is a lot.
So I figured 1 mm was a fairly normal level of thickening.
In any case, we’re getting pretty far afield of the thread topic . Maybe 1% total head variation is a little on the high side, but I think a couple tens of grams difference day to day is plausible, and maybe more if you count hair and… a large double chin.
. Maybe 1% total head variation is a little on the high side, but I think a couple tens of grams difference day to day is plausible, and maybe more if you count hair and… a large double chin.