# Mass distorting spacetime

1. Apr 22, 2004

### jlorino

ok if gravity is mass distorting spacetime then how does mass distort it like a bowling ball on a rubber membrane?
i would think it would need something to pull it down

2. Apr 22, 2004

### Severian596

LOL, it's an analogy so it's lacking the precise nuances you're looking for. I personally don't believe we humans are equipped to visualize (in 3D) the warping of 4D spacetime. The same way stick figures can't comprehend a sphere...they can glance it with a series of circles that grow, then shrink, but they can't think or visualize in 3D.

The bowling ball analogy uses gravity (the ball pulling the membrane down) to define gravity. Don't get caught up in the analogy, just revel in the evidence that supports the theory. :D

3. Apr 23, 2004

### jlorino

ok but what are the factors that warp spacetime?

4. Apr 26, 2004

### Stevo

I personally think that it's a mistake to interpret gravity as being identical to spacetime, and thus mass as deforming spacetime just as the analogous case where a bowling ball bends a rubber sheet. I think then we're basically talking about container space (a legacy of Newtonian physics) and one thing that general relativity shows, I believe, is that spacetime does not contain massive objects.

Remember that the gravitational field couples universally since it is generated, and effects, massive objects. Every object we can empirically experience has mass (mass-energy) so every object generates, and is influenced by, a gravitational force. Because of this, we can then use the gravitational field to define relative distances and relative acceleration. These relative distances and relative accelerations come in the form of the metric.

So gravity is not identical with spacetime. Gravity constitutes spacetime. What we perceive to be spacetime is a phenomenological manifestation of the gravitational field.

So why do we "perceive" spacetime to be warped? Because that is the way the gravitational field propagates.

5. Apr 27, 2004

### jlorino

o ok i get it now
i was just reading "The Elegant Universe" by Brian Greene