Hart titled “Explanation for the Absence of Extraterrestrials on Earth”. The conjecture is the first of many proposed solutions to the Fermi paradox (the conflict between the lack of obvious evidence for alien life and various high probability estimates for its existence).

There is no conclusive evidence of extraterrestrial life. However, there are some theories that attempt to explain the absence of extraterrestrials on Earth: 

• Firstborn hypothesis This theory states that humanity is the first intelligent life in the universe. 
• Fermi paradox This theory asks why the galaxy has not been colonized already, given that there are many stars older than the Sun. 

The science of extraterrestrial life is known as astrobiology.

Earth is the only planet in our solar system where life is known to exist. Here are some reasons why life is possible on Earth: 

• Distance from the Sun Earth is at the right distance from the Sun to receive heat that is not too hot or too cold. 
• Water Earth is in a narrow range of the Solar System where most water is liquid. Liquid water is essential for life. 
• Atmosphere Earth’s atmosphere protects us from harmful solar radiation. It also contains greenhouse gases that keep Earth warm. 
• Chemical ingredients Earth has the right chemical ingredients for life, including carbon, oxygen, and nitrogen. 
• Other components Earth has three components that make life possible: lithosphere, hydrosphere, and atmosphere.

The firstborn hypothesis is a proposed solution to the Fermi paradox which states that no extraterrestrial intelligent life has been discovered because humanity is the first form of intelligent life in the universe.

The Fermi paradox is the discrepancy between the lack of conclusive evidence of advanced extraterrestrial life and the apparently high likelihood of its existence. As a 2015 article put it, “If life is so easy, someone from somewhere must have come calling by now.

The Hart–Tipler conjecture is the idea that an absence of detectable Von Neumann probes is contrapositive evidence that no intelligent life exists outside of the Solar System.This idea was first proposed in opposition to the Drake equation in a 1975 paper by Michael H. Hart titled “Explanation for the Absence of Extraterrestrials on Earth”.The conjecture is the first of many proposed solutions to the Fermi paradox (the conflict between the lack of obvious evidence for alien life and various high probability estimates for its existence).In this case, the solution is that there is no other intelligent life because such estimates are incorrect.The conjecture is named after astrophysicist Michael H. Hart and mathematical physicist and cosmologist Frank Tipler.

The dark forest hypothesis is the conjecturethat many alien civilizations exist throughout the universe, but they are both silent and hostile, maintaining their undetectability by humanity for fear of being destroyed by another hostile and undetected civilization.In this framing, it is presumed that any space-faring civilization would view any other intelligent life as an inevitable threat,

The berserker hypothesis, also known as the deadly probes scenario, is the idea that humans have not yet detected intelligent alien life in the universe because it has been systematically destroyed by a series of lethal Von Neumann probes.The hypothesis is named after the Berserker series of novels(1963-2005) written by Fred Saberhagen.

Astrobiology is the study of life in the universe. It includes the study of the origins, evolution, distribution, and future of life in the universe. Astrobiologists study the possibility of life beyond Earth, and how life can survive in different environments. They may study the simplest forms of life on Earth, or those that live in extreme conditions

Astrobiologists may work on research projects covering: 

• Animal muscle evolution 
• Plant adaptation 
• Extreme life on Earth 

Astrobiologists should have: 

• An aptitude for biology, geology, chemistry, astronomy, microbiology, molecular biology, biogeochemistry, oceanography, and mathematics 
• A systematic approach to solving problems 
• An inquisitive mind 

To become an astrobiologist in India, you may need: 

• Physics, chemistry, biology, or maths in 10+2 
• JEE advance scores for undergraduate admission 
• A Master’s degree in the applicable branch for a PhD

There is no reliable or reproducible evidence that aliens have visited Earth.No transmissions or evidence of intelligentextraterrestrial life have been detected or observed anywhere other than Earth in the Universe. If intelligent life existed it would have produced enough von Neumann probes to cover the universe by now,which runs counter to the knowledge that the Universe is filled with a very large number of planets, some of which likely hold the conditions hospitable for life. Life typically expands until it fills all available niches.These contradictory facts form the basis for the Fermi paradox, of which the Hart–Tipler conjecture is one proposed solution( full article source google)

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