An Isaac Asimov teaser

In one of his fairly lighthearted but factual books, Isaac once posed a question that went something like this:

What if one day we all woke up and everything was twice as big as before. EVERYTHING. How could we tell?

Please keep in mind that this sudden increase applies to all our measuring tools, wave lengths, etc.

To appease our nit picking brethren, do we need to amend the question to have the transformation occur all across the universe in nothing flat? If yes, so be it.

If I remember correctly Asimov’s question might have been inspired by the then new - and bigger - coke bottle that had recently come out. If you were on a desert island and saw this bottle float by, you might conclude you had shrunk.

Anyway, if memory serves, Asimov thought there is no way we could tell.

Curiously enough, however, I found a possible answer in another of Asimov’s books! (Again, a factual work.) But just when I decided to drop him a line, he died.

So, what are your ideas on the subject?

I’ll hold off on my answer until we have some inputs from you all.

Would speed change, too? If the speed of light remained constant, then it would serve as a measuring tool, wouldn’t it?


If everything changed including your physical and mental body then no, you could not tell.

If your physical person was the only thing that did not change, and your cognition remained the same, then of course you could tell.

I don’t know if Asimov considered the speed of light. Do with it as you see fit, please.

In the spirit of the question, today’s light year would be twice as long, as yesterday’s, wouldn’t it? But we would still perceive it as the same old 6 trillion.

The same goes for the time interval. Today’s second is twice as long as yesterday’s.

I think.

The physical person doubles, too.

As everything else becomes bigger, the force of gravity needs to become smaller in order for us not to notice.

If the physical person doubled too, yet their thinking remained as it were, the yes they would be able to tell. They would need situational amnesia to “forget” everything was smaller the day before, no?

I’d start by consulting the engineers and the physicists on structural strength. We know that if you enlarge a perfectly sound structure by a factor of two you may end up with a structure that can’t support its own weight, let alone perform all the tasks the original did.

Of course the usual assumption is that the size-doubled object is composed of atoms, molecules, etc, of the usual size — just many many more of them. Double the length, square the area, cube the volume?

So…if we size-double the elementary particles, do the bonds and forces that make them work on their normal scale do a nice linear-proportional scale-up, or would (let’s say) a hydrogen atom of double its conventional dimensions cease in any meaningful way to be a hydrogen atom as we know it? Do the strong forces and weak forces scale up cleverly along with the size-doubling of atomic and molecular volume, or would we immediately hit contradictory requirements that could not be simultaneously met?

(Exactly how does one interpret and implement in the imagination the concept of an electron of “twice its normal size” anyhow? They aren’t really like little blue marbles with minus signs painted on their sides…)

And yeah, the light thingie.

As AHunter3 says, if everything just doubled in size we’d notice as soon as our knees collapsed.

I propose a follow up question: Is there something you could adjust all the physical laws to to hide it?

For the purposes of this hypothetical, what does “twice as big” mean exactly? Does the Earth double its diameter, or its volume?

(I guess it doesn’t really matter, but I figured I’d ask.)

You’ll also get a lot hotter since your surface to mass ratio would drop. Oh, and your lungs won’t work as well too.

I’m not sure about using the speed to light since our measuring units would change too.

I"m not sure if some of these arguments would hold.

If EVERYTHING is doubling in size, then so should all the atoms and molecules. So the number of molecules in the bridge are the same, they’re just bigger.

If the speed of light stayed the same, then you would know right away. Electronic components such as computers would slow down and may not work at all in some cases and the GPS satellites would stop working because of their dependence on relativity. That would be known instantly be many people. Because the speed of light is the one constant in the universe, I think it would be silly for him to say that changed too because then you just changed the laws of the entire universe. Once you get to that point, it is about a good mind exercise as saying “If my grandmother had balls, she would be my grandfather”.

Actually, Isaac sort of answered this in his second “Fantastic Voyage” novel - the one without Raquel Welch. A kidnapped American scientist and the Russian running the miniaturization lab are shrunk to 50% of their size. To prove it isn’t just a trick with holograms or something like that, the Russian points out that while mass is proportional to length cubed, strength is proportional to length squared (actually the cross sectional area of the muscles). So if you are reduced in size by 50%, your mass decreases by a factor of 8, but your strength decreases only by a factor of 4, resulting in an apparent doubling of strength. She then easily lifts him over her head.

So if everything doubled in size, you’d appear to be half as strong as you were before.

I am assuming that this doubling in size does not affect the actual content of items? As in, while a 1kg bag of apples doubles (and thus weighs 2kg), the packaging will still say 1kg. And given that all weights would be double what the packaging said, we’d know something was up.

Or perhaps that’s too simple, and you’re looking for a more scientific response?

Perhaps given that molecules are based on atomic weight, doubling of these may cause Hydrogen with an atomic mass of 1 would now have an atomic mass of 2, and other elements who’s atomic masses are relative to Hydrogen would also double, meaning that the actual makeup of everything is altered. Water may no longer be water, and I think we’d notice that.

IANA a physicist. However, I would think that if all the fundamental constants of nature change proportionally so that dimensionless quantities remained the same, we would not notice.

More on this is discussed here: