Is Gravity the Same Everywhere?

One of the big questions in astrophysics is about variation of the laws of Physics.  The laws we know and are familiar with; angular momentum, gravity, energy, are the same everywhere on Earth.  But what about beyond Earth? The universe is so large and so vast, we may be in a local region where the laws of Physics are set, and our laws may be different from a distinct region somewhere else in the universe.

A Pulsar and a White Dwarf used to test Gravity across the cosmos. Credit: B. Saxton (NRAO/AUI/NSF)

The good news is that we can make predictions based on our understanding of physics. And with our powerful telescopes that allow us to view a variety of astronomical events from all over the universe, we can test these predictions to verify that the laws we know apply everywhere. Astronomers are constantly looking for new and innovative ways to test predictions.

Astronomers working with the National Science Foundation (NSF) have done just that, in a painstakingly precise 21-year long study of a distant Pulsar.  A pulsar is a collapsed star made mostly of neutrons, sometimes spinning as quickly as 10 times per second! This rapid spin produces intense magnetic fields and releases powerful jets of radiation.  When those jets point toward the Earth they can be observed as a ticking of sorts, keeping very good time.

This particular pulsar has a white dwarf companion star, and has a 68 day orbit, which is unusually wide for a system of this type.  But it is necessary for this experiment to study the effects of gravitational radiation, which is  the steady conversion of orbital velocity to gravitational waves as predicted by Einstein.  If the gravitational constant was at all different, the resulting waves would have an effect on the timing of the pulsar.  However, over the 21 years of the experiment, everything seems to be normal.

Lead author Weiwei Zhu, formerly of the University of British Columbia, says  “The gravitational constant is a fundamental constant of physics, so it is important to test this basic assumption using objects at different places, times, and gravitational conditions. The fact that we see gravity perform the same in our Solar System as it does in a distant star system helps to confirm that the gravitational constant truly is universal.”

As far as we know, gravity is the same, but new theories and ideas will ultimately come forward, with the sheer uncertainty of our cosmic understanding.  dark matter and dark energy are two mysterious concepts we know little about, and they are testing the limits of our scientific capacity.  Perhaps gravity acts differently on the largest scales, and this is where the great mystery of dark energy comes from.  Or maybe, as I’m inclined to think, its far more complex and magnificent.

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