Gravitational Wave Impact

Question

1. What would we see and feel if the waves were powerful enough?

2. Do the waves influence whatever they pass through like a pressure wave would?

3. Or would they be more transparent to the subject there passing through and only visual to the observer? Similar to the bending light?

Answer 1

Gravitational waves literally change the shape of space. So if their effect was much MUCH bigger, a person's body would be accordingly distorted to an observer. In fact, this is how we managed to detect the presence of gravity waves at all. A miniscule change in the length of the path a laser beam had to travel indicated the warping of space.

Also you probably wouldn't feel very different because within space your body remains at rest. Similarly in an Alcubierre Drive, you would not feel the spacial distortion around you.

Answer 2

If a source of strong gravitational waves were to occur near enough to Earth, the tidal forces unleashed in the space-time fabric might tear the planet and us to pieces through a process known as spaghettification. Depending on the shape, size and propagation of the wave, our bodies might feel the gravitational wave as though we were subject to different gravitational pulls in our different body parts. For example, our legs suddenly might weigh 10,000 pounds while the rest of our bodies weighed 100 pounds. The weight of our legs would stretch our bodies like spaghetti and likely tear us asunder.

A passing gravitational wave creates strain by simultaneously stretching space-time in one direction and compressing it in the orthogonal direction. Gravitational waves travel at the speed of light and have a wavelength and a frequency, and an amplitude that manifests as strain, so if the ripples in space-time were of very long wavelength and small amplitude, they might pass through us without distorting our individual shapes very much at all.

A pressure wave such as a sound wave, unlike a gravitational wave, does not distort space-time. It's pressure front is sensed equally by all parts of our bodies.