Big Bang Theory Question?

The "size" of an individual elementary particle is not like the size of a piece of paper. Size for a particle really means tendency to interact with other nearby particles, i.e. scattering or absorption, and is measured by cross section in units of barns (no, really! - physicists do have a sense of humor, albeit a weird one), and this is determined by quantum characteristics of the particle including mass, charge, and spin. If you add in energy, then the particle also has wave-like interactions based on total energy (including mass), but this doesn't affect normal cross-section.

As far as I know, cross-section is not currently altered by the expansion of space, and since particles as such did not exist in the very early universe (too hot and high-energy), cross-section (and matter) did not exist then.

"If im an observer from the outside watching this happen, does matter expand with space? In other words, if I was an observer watching from the outside, would a single particle expand with space?"

It doesn't really make sense to ask the question from the point of view of being "outside", since the universe is a self-contained phenomenon.

Particles themselves are discrete quantum units. The universe is an immense, expanding volume of space, with matter and energy contained within it. When space expands, matter becomes more and more diluted, unless it is part of a gravitationally-bound system, like a planet, a star system, a galaxy, or a galactic cluster. This is why galaxies appear to be "moving away" from each other. The galaxies themselves are relatively stationary; it is space expanding between them that gives the appearance of recession.

The classic analogy, one which is quite accurate (except one dimension lower than the universe actually is), is an expanding balloon. If you draw a bunch of dots on the surface of a balloon and then inflate it, all of the dots will, even though they themselves are not actually moving, *appear* to move away from each other, precisely the way galaxies appear. The same was true in the very early universe, except the matter and energy in the universe would have been represented by about 10^80th individual tiny dots in a sea of particles that filled the entire volume of the universe, and which became increasingly less dense as the universe expanded. The "single point" you refer to was what is called the singularity, also known as the First Cause, the universe's initial state, the origin point of the universe's temporal continuum, or the beginning mathematical limit of the timeline. In the balloon analogy, this would be analagous to the balloon being deflated all the way down to a single point, where its circumference is zero, and all the energy contained in the universe is compressed, for a duration of exactly zero, into this infinitesimally small volume.

>does matter expand with space? In other words, if I was an observer watching from the outside, would a single particle expand with space?

Depends on which version of string theory you subscribe to... What you're describing is the 'Big Rip' - where atoms will spontaneously decay due to expansion of the universe. The universe is still relatively young - and the Big Rip would occur at some point in the future - far in the future - if it occurs at all. I'm... doubting it will.

>Does matter expand with space? In other words, if I was an observer watching from the outside, would a single particle expand with space?

Sorta.... So, there's a 'flavor' of string theory that says our universe, in addition to creating space as it expands, also *stretches* space that already exists. Atoms must live in this space, and they'll be subjected to it's rules. If the *distance* between two Planck points expands, so must the atom. But, this means that the atom, while increasing in size, still will not increase the strength of the forces holding it together - so... an outside observer would be able to see atoms swelling up like balloons being blown up (though *we* couldn't see it) - until it reached a point where the strong and weak nuclear forces could no longer keep the protons of it's nucleus together.

"...space and time are expanding from a single point..."

If you're thinking of the Big Bang as an explosion, that can be misleading. An explosion happens some 'where,' but as far as is known there was no 'where' until the Big Bang event; essentially that means that the Big Bang happened every 'where' at once. There is no 'center' to the universe; no matter where you are in it, that location will seem to be the center.

You are correct in undertanding that matter does expand along with space. Think of everything in the universe as being embedded in space, sort of like raisins in a loaf of bread. Bake the loaf and its dough (space) expands, carrying the raisins along with it.

Do NOT envision isolated matter itself as expanding. For example, the space within our bodies does not expand along with the cosmic expansion because of the forces that bind its molecules and atoms easily overcome the relatively weak energy that causes the universe as a whole to expand.

From what I've read, no it wouldn't. Gravity (and other forces) holds everything together so while the universe as a whole is expanding, the clusters of matter like galaxy or planets do not because any amount they would have expanded it pulled back in by gravity.

From my understanding, space itself is expanding so that should expand everything within it. Photons expand as they travel through space and become red shifted, allowing us to measure the expansion of the Universe. As I understand it this is in addition to the Doppler Effect.

The point I wanted to make, though, is that on a local scale, gravity is strong enough to counter the effects of expansion. We are not being pulled away from the nearest galaxies but travelling as a group. In fact Andromeda and the Milky Way will intersect in a few billion years. So the expansion of space is probably not affecting particles on a local level.

You are on your way and on the right path. The secret to understanding is to be on the outside, looking in but, in this universe, we cannot do that so we use our minds to create that scenario. I had to do just that to write my theory (below) and how I did it is explained in the theory, as is the whole of the universe. It will take you 20 minutes to read and is written in plain English so is easy to understand. Your comments or questions are welcome should you use the feedback page, OK?

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