# The Sun, Electromagnetic Waves, and Gravitational Waves

## Main Question or Discussion Point

This is a question about electromagnetic waves and gravitational waves.

Let's say we're on the Earth and we're looking up at the sun (safely).
If the sun were --for some reason-- to violently and dramatically jerk from its position, how would we first find out?

Would we first *see* the sun move?
Or would we first detect a change in our orbit?

Would the light, the electromagnetic wave, reach us first, or would the gravitational wave reach us first? Would they happen at the same time?

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I don't know a situation where the sun would jerk from its position but I'm fairly sure that it takes around 8 minutes and 20 seconds for light to travel from the sun to Earth, so you probably wouldn't notice anything until that time had elapsed.

Drakkith
Staff Emeritus
Changes in both gravity and electromagnetism travel at c.

This is a question about electromagnetic waves and gravitational waves.

Let's say we're on the Earth and we're looking up at the sun (safely).
If the sun were --for some reason-- to violently and dramatically jerk from its position, how would we first find out?

Would we first *see* the sun move?
Or would we first detect a change in our orbit?

Would the light, the electromagnetic wave, reach us first, or would the gravitational wave reach us first? Would they happen at the same time?
Same.

Electromagnetic waves have an electric field component and a magnetic field component that are orthogonal to each other.
Is there something analogous to this with gravitational waves?

Drakkith
Staff Emeritus
Electromagnetic waves have an electric field component and a magnetic field component that are orthogonal to each other.
Is there something analogous to this with gravitational waves?
Not to my knowledge. I believe the wave is in the metric and only has one "component" if you will.

Matterwave
Gold Member
Gravitational waves have 2 independent components of the metric corresponding to the 2 possible polarizations.

Drakkith
Staff Emeritus
Gravitational waves have 2 independent components of the metric corresponding to the 2 possible polarizations.
I assume this is different than the electric and magnetic components of an EM wave?

mfb
Mentor
It is different - but you can compare it to two orthogonal polarizations of light.

Drakkith
Staff Emeritus
It is different - but you can compare it to two orthogonal polarizations of light.
Got it.

Gravitational waves have 2 independent components of the metric corresponding to the 2 possible polarizations.
LIGO (Laser Interferometer Gravitational Wave Observatory) was built to detect such waves....but as far as I know, they have not found anything. So at this point gravity waves are still theoretical....right?

Drakkith
Staff Emeritus
LIGO (Laser Interferometer Gravitational Wave Observatory) was built to detect such waves....but as far as I know, they have not found anything. So at this point gravity waves are still theoretical....right?
I'd say so. We expect to find them as GR has been right about most observed effects so far, but we just haven't been able to locate the suckers yet!

Physicist50
Gold Member
Changes in both gravity and electromagnetism travel at c.
Wouldn't the speed of a gravitational wave depend on the mass of the object, (in this case, the sun) and the warpage of space-time?

Drakkith
Staff Emeritus