The potential for an identical Earth-like planet to detect Earth depends on several factors, such as the technology available on this hypothetical planet and the method of detection used. If the twin Earth has advanced technology akin to or beyond human technology, it could feasibly detect Earth using methods similar to those astronomers on Earth use to find exoplanets. These methods include:
Transit Method: If the twin Earth is positioned such that Earth’s orbit passes in front of the Sun from its perspective, it could detect a periodic dimming of the Sun as Earth transits. This dimming is a telltale sign used by astronomers to identify planets orbiting other stars.
Radial Velocity Method: By observing slight changes in the Sun’s spectrum caused by Earth’s gravitational pull (even though this is challenging with a planet as small as Earth), signs indicating Earth’s presence could be detectable if the twin Earth possesses exceptionally sensitive instruments.
Direct Imaging: With technology capable of blocking out the Sun’s overwhelming brightness, the twin Earth could attempt to directly image planets. Given current advancements in astronomy, techniques like coronagraphy and starshades would be essential.
Astrometry: Measuring the precise movements of the Sun across the sky could reveal a slight wobble induced by Earth’s gravitational influence. This requires highly accurate instrumentation.
Gravitational Microlensing: Relying on random cosmic alignments with background stars, this method could yield indirect detection under very particular circumstances.
Ultimately, the success of detecting Earth from a twin planet hinges largely on the alignment of observational opportunities and the technological prowess the twin Earth possesses to employ these sophisticated techniques.