View Full Version : Is there a limit to how small an object can be

2009-Mar-24, 08:54 PM
Hi there im new here just found this forum and some really nice articles here.

a question has been nagging me for a while and i was wondering if anyone could help shed light on this one for me. In theory is there a limit to how small an object could be?

With space expanding as it is there is going to be more room and bigger galaxies can develop. Could there be galaxies so small that we cant ever perceive them?

Sorry if my question doesnt seem to well thought out.

2009-Mar-24, 09:25 PM
In theory is there a limit to how small an object could be?

The ancient Greeks wondered about that, and probably also did those upon whose shoulders they stood.

They wondered if you can keep on cutting an object, like cutting it in half, forever and ever. Through reasoning they conceived of an uncuttable stage, the realm of the smallest possible object and named it "atom", a- for "not" and the root tom for "cut".

Centuries later scientists confirmed the existence of atoms. And not so very much longer after that, new scientists described the even smaller parts of which atoms are made -- since they were "cuttable" after all. But those parts, the quarks and leptons, are the smallest particles we conceive of now. We don't know if we are at the final limit of cutting, but the current theory of quantum mechanics throws up some pretty firm limits on what we can ever measure.

Ask a particle physicist from the future.

Can a galaxy be smaller than, say, a planet? Not by the definition of what a galaxy is.

2009-Mar-24, 09:46 PM
Welcome to BAUT JamesT.

Theoretically, Quantum mechanics says that elementary particles are 0 dimensional points. String theory says they are 1-dimensional strings, with a length equal to the Planck length (1.616 252 10-35meters), which is much smaller than we could ever observe. It has been estimated that to explore this scale, we would need a collider the length of the Milky Way.

I doubt we will ever know what the lower limit is in reality within the foreseeable future...

2009-Mar-24, 11:34 PM
You might postulate that all the matter in the Universe ( ~about 1084 protons (I'm taking the liberty of ignoring electrons' mass ) be converted to energy using E=mc2. Then let that be part of a single photon. Since E=hv holds, and (v)(Lambda)=c....c/v yields avery, very, short photon, holding all of the energy of the universe. Yes I'm ignoring all the energy not in mass, too......lighten up.

Since you're new here....the proof is left as an exercise for homework....:shifty::doh::lol: pete

2009-Mar-25, 01:38 AM
With space expanding as it is there is going to be more room and bigger galaxies can develop.

Just thought I'd correct one misconception; Expansion doesn't make galaxies any bigger, it makes the space between galaxies bigger. Galaxies, and clusters and superclusters thereof, are bound together by gravity, and stick together even as space they occupy expands. They won't get any bigger in and of themselves, unless a "big rip" occurs: http://en.wikipedia.org/wiki/Big_Rip
...Which is highly speculative and far from a given at this point.