Question #4647c

1 Answer
Nov 28, 2014

No.

Gravitational force exists between any two objects in proportion to the their masses and the distance between them.

#F = (GM_1M_2)/r^2#

Here #G# is the universal gravitational constant, #M_1# and #M_2# are the masses involved, and #r# is the distance between them.

Electrical charges come in two varieties, positive and negative. Like charges repel each other and opposite charges attract each other.

Magnetic fields also can be attractive or repulsive. However, it is not possible to isolate a magnetic "monopole." That is, you can never have a north pole without a south pole.

Gravity is something different. In all earth-based measurements, it is never repulsive. Gravity only attracts. Some advanced theories suggest that it is gravity which sets a direction for time. One might say that gravity only attracts things because time only moves forward. But these theories remain untested.

There are some curious observations from astronomy. Using the equations for gravity above, and having a pretty good guess for the mass of stars and clouds of dust in space, we can make predictions of how fast stars should be moving around their galaxies. And, they move faster than expected. This suggests that there is more mass there which we cannot see (dark matter). Or, perhaps that equation for gravitational force is not valid when #r# gets very very large.

Even more curiously, astronomers have shown that the universe is expanding. The distances between the galaxies are increasing. As if it came from some massive explosion, galaxies farther away are moving faster than galaxies closer to ours. If galaxies flew off at a variety of speeds, the ones moving faster should be farther away. That much seems to fit into one sensible theory. New observations since about the year 2000 have found that galaxies are actually accelerating away from each other. This suggests that some force is pushing them apart. The force is called "Dark Energy." We have no explanation.