# Expansion of the Universe, cop this!

1. May 30, 2005

### Ryan Lucas

Hi! Im doing year eleven physics and love it, im a teachers pet and all. Anyway, I have this theroy with my physics teacher, we came up with it together its really cool. So anyway, the expantion of the universe is accelerating, "defying gravity". Anyway, lets assume that it keeps accellerating infinitely. Now eventually the expansion of the universe must reach near light speed right? now an object travelling at near light speed GAINS MASS, it weighs more. Now with a higher mass, it thus has more gravity, more gravity means that the accelerating expansion of the universe must slow, Ergo universal equilibrium!!!

Have you got any thoughts on my theory? Can you disprove it? Please do!!!!

2. May 30, 2005

### Danger

If I'm understanding it correctly, it would appear to be another case of misunderstanding the expansion of the universe. The things in the universe are not moving relative to the space they're in; the space itself is expanding. Therefore, no relativistic mass increase.

3. May 30, 2005

### Staff: Mentor

I'll move this to the General Astronomy and Cosmology section, where experts aplenty will inform and delight you!

4. May 30, 2005

### GOD__AM

An accelerating body does not have more gravity or mass. What you are talking about is relativistic mass, and that does not add to the weight of an object. Consider an object falling to earth. As it gets closer there is acceleration due to gravity, so the object speeds up. It does not change its weight as it is falling. When it hits the ground it may leave a deep impression, deeper than it would have if it was dropped from less of a height. This is because of the objects inertia and not its weight which remains constant.

5. May 30, 2005

### Nereid

Staff Emeritus
Welcome to Physics Forums, Ryan_Lucas!

As Danger already mentioned, part of your idea is one of the most common misconceptions about cosmology (and GR). There's a recent issue of Scientific American with an article by Lineweaver (he of UNSW) on this (and other) misconceptions. IIRC, there's a link to an online version of this article in another thread here in GA&C. If not, I'm sure a quick google will find it. If you're interested, here's a more technical paper by Lineweaver and his colleague, Tamara Davis

6. May 30, 2005

### Ryan Lucas

Mmmm, thanks for your responses, they really helped. By the way, am i right that when they reach NEAR LIGHT velocity, an object will gain mass? This is shown by Einstien's famous formula?

7. May 31, 2005

### Danger

An object gains relativistic mass with every increase of speed. (And keep in mind that velocity is a vector, as opposed to speed which is a scalar measurement. ie: velocity requires a direction as well as a speed. This is why something veering off on a tangent to its original course undergoes a change of velocity even if its speed remains constant.) You have the right basic idea, but serious refinement of it is necessary.

8. May 31, 2005

### Chronos

If you were co-accelerating with the body in question, you would both swear neither of you gained a pound.

9. May 31, 2005

### Danger

I am so tempted to make a Jenny Craig joke here, that I think I shall head down to GD before I say something embarrassing.

10. May 31, 2005

### Anomalous

This is cool man

If what U r saying is right then all the objects apporaching speed of light must collapse into BlackHoles, Wow I never thought of that before. All this is vrey enlightening.

11. May 31, 2005

### matt.o

no, that is incorrect. the mass of the object in it's own reference frame does not change, hence it doesn't collapse into a black hole.

12. Jun 1, 2005

### Anomalous

O yaa

Then where is the resistance to the acceleration comming form as we approach highere speeds ? Or is it an problem limited to the particle accelerators only.

13. Jun 1, 2005

### matt.o

actually, I think relativistic mass may contribute to a gravitational field, I am no expert here! nevertheless, the mass has to be confined within a region such that the density must be high enough to form a black hole. mass alone does not cause a body to collapse into a black hole, extreme densities are needed.

14. Jun 1, 2005

### Danger

That's where the 'relative' part of 'Relativity' comes in. To itself, the object undergoes no change. Relative to an outside observer, it gains mass, shortens, and has its time slowed. If, for instance, the Earth were to speed up in its orbit, taking you with it, you would still weigh the same on your bathroom scale even though you are moving faster. Someone on Mars would think, "Jeez, that guy's getting heavy!"