Exploring Gravitational Lensing: Does It Enhance the Felt Gravity of a Galaxy?

Gravitational lensing remains one of the most fascinating phenomena in astronomy, allowing us to observe galaxies behind massive structures and magnify their observed light. However, the question of whether this lensing can also enhance the felt gravity of the observed galaxy has been a subject of much debate. Let's delve into the details.

Understanding Gravitational Lensing

Gravitational lensing occurs when the light from a distant galaxy (or any celestial object) is bent by the gravitational field of an intervening mass. This phenomenon has been well-documented and provides valuable insights into the universe. It is primarily a bending of light, not gravity. The light from all the stars comprising a galaxy constitutes a negligible contribution to the gravitational field created by the galaxy's entire mass/energy. Similarly, the light crossing the given galaxy from other galaxies in the universe makes even a smaller contribution.

A gravitational lens, typically a cluster of galaxies closer to us than the source, can focus the light and make the galaxy appear larger than it would otherwise. This magnification is purely an optical effect and does not affect the source's gravitational field in any way. Hence, the gravitational force felt by the galaxy remains unchanged.

The Fallacy of Enhanced Felt Gravity

The concept of "felt gravity" is not a physical reality. The gravitational force between two objects depends on their masses and the distance between them, not on any relativistic effects. Therefore, the observed magnification of a galaxy does not translate to a change in the felt gravity of that galaxy.

Let's consider a specific example: Einstein's Cross. This quadruply-imaged quasar exhibits a magnified appearance due to the gravitational lensing effect from a foreground galaxy or cluster. While the observed light is significantly enhanced, the felt gravity of the quasar or the galaxies appearing as Einstein's Cross remains the same. There is no physical mechanism that would allow the observed magnification to translate into a change in the gravitational field's strength.

The Impact of Gravitational Lensing on Gravitational Waves

Another related topic is the impact of gravitational lensing on gravitational waves. Gravitational waves, like electromagnetic waves, will be affected by gravitational lensing. The continuum of any wave is subject to the same geometric impact by gravity. Gravitational waves propagate through space-time and can be distorted by the gravitational field of dense objects. Theoretical models of gravitons, if they exist, would also be subject to lensing, much like other massless particles.

Let's consider the implications of gravitational waves being affected by lensing. If strong gravity affected other similar wavelengths, it would create a paradox. For instance, how would gravity propagate through the universe if it were subject to gravitational lensing? How could gravity escape the strongest known gravitational field, just outside a black hole's singularity, if it were subject to such a distortion?

To summarize, while gravitational lensing magnifies the observed light of a galaxy significantly, it does not enhance the felt gravity of the galaxy. The magnification is purely optical and has no physical impact on the gravitational field strength. Gravitational waves, being affected in the same way as electromagnetic waves, further support this understanding.

Conclusion

Despite the intriguing nature of gravitational lensing, it remains clear that this phenomenon does not affect the felt gravity of a galaxy. The observed magnification of light due to lensing is a fascinating aspect of astronomy that enhances our understanding of the universe but does not alter the fundamental properties of gravity as we know them.

Keywords

Gravitational lensing, gravitational field, gravity, Einstein's Cross