Rubber sheet analogy - density change

In summary, when a rubber sheet with a bowling ball in it stretches, the density of the rubber decreases as the molecules become more spaced out. However, this analogy does not accurately represent the concept of space-time. In reality, the distances along space-time dimensions (the metric) change and there are no particles of space-time involved. It is a smooth manifold with a intrinsic curvature, and objects move on geodesic paths.
  • #1
Pjpic
235
1
When the rubber sheet with the bowling ball in it stretches, the density of the rubber is lowered as the rubber molecules become more widely separated by empty space. Are there particles of space time(?) that are similarily separated by more empty space when when the amount of nearby mass(?) changes?
 
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  • #2
Pjpic said:
When the rubber sheet with the bowling ball in it stretches, the density of the rubber is lowered as the rubber molecules become more widely separated by empty space. Are there particles of space time(?) that are similarily separated by more empty space when when the amount of nearby mass(?) changes?

No. You are stretching the rubber sheet analogy too far.

(:biggrin:)
 
  • #3
DaveC426913 said:
No.

If the amount of mass changes space time, what is changing? If there is a measurement and the numbers are changing, what whole does each interger represent?
 
  • #4
Pjpic said:
When the rubber sheet with the bowling ball in it stretches, the density of the rubber is lowered as the rubber molecules become more widely separated by empty space. Are there particles of space time(?)
The rubber sheet usually represents only space, and is therefore misleading. See post #4 in this thread:
https://www.physicsforums.com/showthread.php?t=286926
Pjpic said:
If the amount of mass changes space time, what is changing?
The distances along space-time dimensions (the metric) change. Space-time is "streched" but there are no "particles of space time" in the model. It is a smooth manifold with a intrinsic curvature, and free falling objects are moving on geodesic paths.
 

1. What is the rubber sheet analogy?

The rubber sheet analogy is a way to explain changes in density by using a stretched rubber sheet as a visual representation. When an object is placed on the sheet, it causes a dip or indentation in the sheet, similar to how an object placed in a fluid causes a change in density.

2. How does the rubber sheet analogy relate to density changes?

In the rubber sheet analogy, the weight of the object placed on the sheet represents the mass of a substance, while the indentation in the sheet represents the change in density caused by the object. The deeper the indentation, the higher the density change.

3. Can the rubber sheet analogy be used to explain changes in density in all substances?

Yes, the rubber sheet analogy can be used to explain changes in density in all substances, as long as they are in a fluid state. This includes gases, liquids, and even semi-solids like magma.

4. How does the rubber sheet analogy help us understand changes in density in real-life scenarios?

The rubber sheet analogy helps us visualize and understand changes in density in real-life scenarios. For example, it can help us understand why ice floats on water, as it is less dense than liquid water and causes a less deep indentation in the rubber sheet.

5. Are there any limitations to the rubber sheet analogy?

While the rubber sheet analogy is a helpful visual tool, it is important to note that it is not a perfect representation of changes in density. In reality, changes in density can also be affected by factors such as temperature and pressure, which are not accounted for in the analogy.

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