am I expanding with the universe?

since all the galaxies are distancing themselves and “expanding”… are the atoms in my body doing the same thing? when I wake up in the morning am I farther apart from my bed than when I went to sleep?

I would assume it safe to say “No”. If EVERYTHING were expanding - you, me, Earth, atoms, quarks, etc. - then we would never be able to tell, as the detection equipment would also be expanding.

Think of it this way… measurement is really just a system of comparing an object to a set standard. But what if the standard were also expanding?

My understanding is:

All of space is constantly expanding.
As we speak, the space between the atoms in your body is expanding.
It’s expanding very very slowly. The forces of gravity, and the other forces that are keeping your body/the earth/etc together significantly outweigh the expansion by many orders of magnitude.

So maybe the expansion of space would have caused you to wake up a millionth of a zillionth of meter further from your bed, but gravity had no problem overcoming that and pulled you back to your normal bed/body distance.

[small]By the way, I am not a physicist[/small]

On the other hand, I am expanding as is proved by the results on my bathroom scale this morning.

Physically quantifying the expansion of the universe by some sort of measurement is a rather thorny issue. This is because the universe and everything in it (including all of our measuring devices) undergo the same effects from expansion. We can’t just take a measurement of some 1-meter long standard rod, and then re-measure it again later because the rod and the measuring tool will have expanded. The only way to measure expansion is to use something that is independent of the effects. This happens to be time. By bouncing LASER pulses mirrors separated by very large distances, two travel times can be compared, and expansion can be measured.
This type of experiment has not yet been perfected. The tolerances are so fine that signal is virtually indistinguishable from noise.

Gentlemen, while I enjoyed your speculations, I must inject some conclusions based on observed data: No, facough, you are NOT expanding with the Universe.

Hubble’s observation in the 20’s that the Universe is expanding is based on the Doppler shift toward the red end of the spectrum of light reaching us from distant galaxies. You and I, the Earth, our Solar system, our Galaxy and the handful of galaxies closest to us, forming a cluster, remain at approximately the same distance from each other as time goes on. The expansion leading to the Big Bang theory and most of modern cosmology applies only to the space beween our galactic cluster and other galaxies and clusters.

I suggest a Google search on “Hubble expansion” or some such for a long, long list of citations. Here’s the first I happened to come across:

There are different forces that act over larger distances. We are not expanding because we’ve got forces keeping us bound. The Andromeda galaxy is moving toward us, and so the expansion of space only occurs at great distances - between clusters of galaxies. We dont have a good explanation of why, but no, we are not expanding, the earth isnt expanding, and our galaxy isnt expanding either.

The Hubble Constant (the rate at which the universe is expanding) is on the order of 75 km/s/Mpc (approximately). That means if two objects are one megaparsec apart, they will be moving away from each other at a speed of 75 km/s due to expansion of the space between them. If they were seperated by two megaparsecs, they’d be moving apart at 150 km/s, etc. Now, a megaparsec is a hell of a long way. On the order of 3.26 million light-years (3.086 x 10^22 meters). So, if the top of your head and the bottom of your feet are 2 meters apart from each other (6.48 x 10^-23 megaparsecs), they will be moving apart from each other at a speed of (6.48 x 10^-23) * (75 km/s/Mpc) = 4.86 x 10^-21 m/s due to universal expansion. The diameter of a proton is about 1.6 x 10^-15 m, and this is a million times smaller than that. Electromagnetic forces are easilly able to resist this expansion and hold your body at the same size.


Aww, shoot, bryannmcc, I was all ready to pull down my New York Times Science Desk Reference and plug in some numbers and you beat me to the punch.

I would just like to add that if we were expanding, we might see some interesting side effects, given various assumptions. If the various particles that you are made up of are not expanding, just the spaces between, you’d see yourself getting sorta rarefied. But even if we ignore the electromagnetic effects that bryannmcc so rightly pointed out, it still doesn’t amount to much. According to my admittedly hasty calculations, the total amount if expansion experienced by a two meter tall being who had lived from the origin of life on earth about 4 billion years ago to the present day would be 6.131 X 10^-4 meters, or about half a millimeter. And yes, I know that there were no 2 meter beings on Earth 4 billion years ago. I’m speaking in my blue-skying hypotheticalizing mode.

Sorry ForgottenLore. :slight_smile: If it’s any consolation, I am beginning to think I may have screwed up my powers of ten in there somewhere. Feel free to check, if you like. I believe it should be 4.86 x 10^-18 m/s, which is only (;)) a thousand times smaller than a proton.

More fun facts: The distance from the earth to the sun would be increasing at a whopping 3.64 x 10^-7 m/s, or about a meter every month. If, that is, it weren’t for all that gravity.


No discussion of this is complete without a link to the last time we covered this. Classic thread.