In an event immortalised in this Google Doodle, at 4 minutes past midnight (GMT) on Jan 1, 2017, the density of Helium suddenly and inexplicably increased from 0.1664 g/L (at normal temperature and pressure) to 1.664 g/L (in the same situations), a tenfold increase of its apparent weight.

Other than causing balloons to tumble in comical fashion, this clearly had many not-quite-so-apparent effects. What were they, and what caused the most disruption to everyday life? How did we find replacements for those uses of Helium that were disrupted by this change? What impact did this event have on society?

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    $\begingroup$ does this phenomenon also aply on the sun? That would triple its mass. And the fusion reaction H+H=>He might not work anymore $\endgroup$
    – Madlozoz
    Jan 1, 2017 at 19:32
  • $\begingroup$ Are you sure in your mass data? I'd place lower bound on Helium's mass so that regular baloons would lose buoyancy, and a higher bound on assuming that baloons in that doodle travel at terminal velocity (since they don't seem to be accelerating) and that would get 2 pretty different numbers. $\endgroup$ Jan 1, 2017 at 20:43
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    $\begingroup$ Density is mass divided by volume. did the mass of helium increase, or did its volume decrease? or both? $\endgroup$ Jan 2, 2017 at 0:51
  • $\begingroup$ @ApproachingDarknessFish - I'm not really sure, except that I think the volume decreasing would imply a change of the ideal gas law, which would likely have effects elsewhere to, so I think it would have to be the mass. But answers for either possibility might be interesting. $\endgroup$ Jan 2, 2017 at 10:56
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    $\begingroup$ This should be posted to XKCD 'what-if?' $\endgroup$
    – G0BLiN
    Jan 2, 2017 at 17:35

3 Answers 3


Everybody would die.

Let's say you have a helium balloon in your house. This balloon, according to the almighty Google, holds 14L of helium.

That 14L is 2.289 grams of helium (if it's an aluminum balloon at STP; if it's latex, it'll be more because it's compressed).

If suddenly that were to become 22.89g of helium... that mass would have to come from somewhere.

(Hint: it's not going to come from nearby mass.)

So it'll come from energy, courtesy of E=MC^2.

How much energy? 2.0573*10^14 Joules.

(Sidenote: you probably have at least 1000 of these in your city right now. That energy is ~1.2x the amount of energy from the sun that hits the earth in one second. This is a LOT of energy.)

How much of an effect would this have?

Well, if you have an 1800 ft^2 house that's, on average, 8ft high inside, you'll have 520.05 kg of air inside it.

That 2e14J of energy would cause a change-in-temperature of that air of 5.511*10^8 K.

(Hint: it's not going to change that much; it, combined with every other balloon, would just freeze the world.)

And that's just the party balloon you still had from the birthday-party last week... Let alone all the other balloons and other uses for helium.

The only other place this mass could come from is other mass - meaning either fusing hydrogen into helium (Hint: releases a ton of energy) or fissioning heavier elements down to helium (Hint: absorbs energy). I haven't run the numbers, but I suspect these would be more damaging.

If you don't want the world to die, don't tag your question as "science-based." You are literally changing a fundamental law of physics for one single element, then changing the laws of physics more to prevent everybody from dying.

  • $\begingroup$ Or that mass could simply be some other mass, e.g. some little bits chipped off Uranus. $\endgroup$ Jan 1, 2017 at 20:39
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    $\begingroup$ "If suddenly that were to become 22.89g of helium" I think you have it backwards. The available mass wouldn't magically change, but the volume taken up by that mass would. Because the density has changed. TL;DR all volumes of hydrogen will suddenly shrink. $\endgroup$ Jan 1, 2017 at 23:30
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    $\begingroup$ @LightnessRacesinOrbit In that case, there would be even more interesting questions as to why intermolecular forces suddenly started acting differently. $\endgroup$
    – Cort Ammon
    Jan 2, 2017 at 1:27
  • $\begingroup$ @CortAmmon: That's right $\endgroup$ Jan 2, 2017 at 13:49

Depends on how the helium suddenly gains weight, and how far-spread that change is.


To make helium become denser, you must increase the weight of the individual helium molecules. Or you need to employ a special kind of magic that restricts the speed of Helium molecules to a fraction of their normal Brownian motion speed (i.e. slows them down and makes it so that they take up less volume for their weight).


If it is throughout the solar system, then the sun will certainly get problems -- it lives off fusing Hydrogen to Helium, after all. If helium is suddenly heavier, then that mass needs to come from somewhere, and that most likely will disturb the regular fusion process. Additionally, all helium that has already been produced and is massing in the sun's core, will become heavier and so the Sun's gravity will increase suddenly, and disturb its nice equilibrium. If helium is just slowed by magic, its volume will decrease suddenly, and so the sun's core will suddenly shrink. In both cases: There will at the very least be horrible solar flares for weeks, if the sun manages to stabilize. If not, we could be dealing with the sun suddenly going nova.

Earth only: If Helium is heavier than air, it will sink to the ground. There are 5.2 parts per million in the atmosphere; a rough estimate has 10km of atmosphere, so helium should pile about 5.2cm high on the ground. Since it will flow from higher ground down to sea level, rowing a boat on the ocean might become hazardous, and I am not sure what the fish in the water (and the ocean-dwelling mammals) will do.

Helium is used in the industry for supercooling magnets etc. It's got a melting point of -272°C, and slowing down its molecules will certainly raise that melting point by tens if not hundreds of degrees. As a result, any and all technical applications that use Helium for cooling, will suddenly run hot.

Helium is also a sideproduct of radioactive decay (alpha rays are helium nuclei). No clue how radioactive decay will be disturbed if suddenly the breaking-off helium cores are fifteen times heavier than normal (that mass needs to come from somewhere, after all). The alpha rays themselves should lose much of their already small penetrating power (can be stopped by a sheet of paper), but since they are a lot heavier they will probably cause a lot more damage when something like Iodine-13 is ingested. Additionally, whereever alpha decay takes place in an enclosed room, you are in serious danger of suffocating (it can't get out, so it will pile up like carbon monoxide).

Tumbling balloons like in your doodle will be the most harmless side effect of heavier helium by far. And, since many DIY youtube instructions for floating balloons all produce Hydrogen from a redox reaction (DO NOT DO AT HOME -- hydrogen is highly flammable, see the Hindenburgh!), there will be many balloons still afloat.

Unless you suddenly make Hydrogen denser, too.

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    $\begingroup$ This answer captures a common challenge for questions such as these. "Helium becomes denser" is tricky because density is a bulk property, and most of science breaks these bulk properties down into smaller parts (such as increasing the molecular weight of helium). Which particular way this is broken down matters for making predictions with science. Science does not like to make predictions without knowing things first. $\endgroup$
    – Cort Ammon
    Jan 1, 2017 at 17:46
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    $\begingroup$ I wonder what the orbit of earth would look like if the sun was suddenly heavier. It'd definitely become very eccentric and we would all burn up and die... if the sun didn't just die out first. $\endgroup$
    – iAdjunct
    Jan 1, 2017 at 19:15
  • $\begingroup$ The ramifications of 5 cm of heavy, inert gas settling to the surface of the earth are probably pretty extreme. Nothing living at that height (ants, beetle, worms, anything living in burrows under the ground) now has any breathable O2 & would suffocate in pretty short order. As a guess, that might have some drastic effects on the ecosystem. Not to mention, how much CO2 is the grass now getting to use for photosynthesis? This isn't looking like it will turn out well... $\endgroup$
    – Ralph J
    Jan 2, 2017 at 20:29
  • $\begingroup$ @RalphJ Well, since the helium is heavier than air, it would flow downward just like water, to accumulate at sea-level. So higher elevations (50m above sea level) should be perfectly fine, with no helium resting there unless it's got a cauldron shape. You'd probably have to take care to not step into the invisible Helium rivers, especially if there is a source that produces natural helium (see radioactive decay) anywhere closeby, but it should not effect nature everywhere $\endgroup$
    – subrunner
    Jan 3, 2017 at 11:10

A ten-fold density increase will kill helium cooled nuclear reactors.

Helium is used for buoyancy, low boiling point (superconductors) and heat transfer/working fluid.

In the latter capacity, helium's monatomic nature and especially its low molecular weight are vital. The only way (under our physics, via the ideal gas law) to increase gas density (at same conditions) is to raise molecular mass. A 10x increase in helium gas density would make nuclear reactors using gaseous helium fail. The increase in density would make the key heat removing mechanism ballpark 10x (it might be a square root effect (but still sqrt(10) ~= 3,16..., my statistical mechanics is hazy) less effective. I wouldn't want to be downwind!

It will also wreak other devices using gaseous helium for as either a working fluid (some Stirling engines) or as a heat transfer fluid in non-nuclear applications (some chip packaging, or was that technology {IBM, I'm pretty sure} abandoned?)

  • $\begingroup$ What reactors use helium? $\endgroup$
    – kingledion
    Jan 2, 2017 at 2:04
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    $\begingroup$ en.wikipedia.org/wiki/Gas-cooled_reactor lists a handful. $\endgroup$
    – Catalyst
    Jan 2, 2017 at 2:11
  • $\begingroup$ As far as I can tell from that link, the only currently operational gas-cooled reactor is in North Korea, and that uses Carbon Dioxide, not helium. $\endgroup$
    – kingledion
    Jan 2, 2017 at 3:02
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    $\begingroup$ @kingledion There are seven second-generation gas-cooled reactors operating in the UK at present (they are due for closure at various dates between 2023 and 2030) but they also use carbon dioxide coolant, not helium. en.wikipedia.org/wiki/Advanced_gas-cooled_reactor $\endgroup$
    – alephzero
    Jan 2, 2017 at 10:47
  • $\begingroup$ So I guess the conclusion is that an increase in helium density won't do anything to any nuclear reactors. $\endgroup$
    – kingledion
    Jan 2, 2017 at 18:26

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