Now, we come to gravitational waves. These are sort of unique, because we’ve only seen the wave-like part of them, never the particle-based part. However, just like water waves are waves that are made of particles, we fully expect that gravitational waves are made of particles, too.

The Penrose Triangle is an impossible figure (or impossible object or undecidable figure): it depicts an object which could not possibly exist. It is impossible for the Impossible Triangle to exist because in order for it to exist rules of Euclidean geometry would have to be violated.

Of the universe’s four fundamental forces (gravity, electromagnetism, and the strong and weak nuclear forces), only gravity lacks the “quantum” description. As a result, no one knows for sure (although there are plenty of ideas) where gravitational fields come from or how individual particles act inside them.

The graviton must be a spin-2 boson because the source of gravitation is the stress–energy tensor, a second-order tensor (compared with electromagnetism’s spin-1 photon, the source of which is the four-current, a first-order tensor). …

Wave–particle duality is the concept in quantum mechanics that every particle or quantum entity may be described as either a particle or a wave. This phenomenon has been verified not only for elementary particles, but also for compound particles like atoms and even molecules. …

Einstein believed light is a particle (photon) and the flow of photons is a wave. The various properties of light, which is a type of electromagnetic wave, are due to the behavior of extremely small particles called photons that are invisible to the naked eye.

As it turns out, there are two directions for light waves to oscillate and, consequently light is a transverse wave.

Transverse wave, motion in which all points on a wave oscillate along paths at right angles to the direction of the wave’s advance. Surface ripples on water, seismic S (secondary) waves, and electromagnetic (e.g., radio and light) waves are examples of transverse waves.

Examples of transverse waves include:

• ripples on the surface of water.
• vibrations in a guitar string.
• a Mexican wave in a sports stadium.
• electromagnetic waves – eg light waves, microwaves, radio waves.
• seismic S-waves.

In a transverse wave the particle displacement is perpendicular to the direction of wave propagation. The particles do not move along with the wave; they simply oscillate up and down about their individual equilibrium positions as the wave passes by.

Sound is a longitudinal wave, while light is a transverse wave. Polarization requires the direction of the wave to be perpendicular to the direction of propogation; only light can do this. Doppler effect, refraction, and interference occur in both wave types.

A wave can be thought of as a disturbance or oscillation that travels through space-time, accompanied by a transfer of energy. The direction a wave propagates is perpendicular to the direction it oscillates for transverse waves. A wave does not move mass in the direction of propagation; it transfers energy.

Also, the vibration is not a transverse wave, but a longitudinal wave. Earthquakes become waves, which spread, shaking the ground. Earthquakes create both longitudinal and transverse waves. Also, one characteristic is that a longitudinal wave’s transmission is faster than transverse waves.