The thing that makes the Universe so terrifying yet beautiful is its unpredictability. Literally anything is possible in our Universe. The Universe is such that one moment you are sipping coffee feeling comfy and confident about life and in the next, Earth becomes a distant memory of the past. The number of ways life could end makes me wonder that either someone is watching over us (not necessarily God) or we are extremely lucky. Keeping that in mind, I will now inform you about the top 10 ways our Universe could destroy life on Earth completely.
1. Rogue Planets: These are planets that have separated from their orbit around its original star and float about freely through the Universe, creating chaos. The interesting thing is that these planets are quite common. Scientists estimate that there are around 50 billion rogue planets in the Milky Way alone. There is a possibility that one of these planets might collide with the Earth ending life as we know it and breaking the Earth into pieces. We could see the planet approaching but it would be impossible to stop it.
2. Galactic Cannibalism: Galactic cannibalism isn't the name of a death metal band, but is an actual phenomenon and could happen to the Milky Way as well. When the size difference between two neighbouring galaxies becomes too big, the smaller one collapses into the larger one due to gravity. Simply put, the larger galaxy "swallows" the smaller galaxy. The galaxy nearest to the Milky Way is the Andromeda galaxy and is much larger than the Milky Way. So, in a few billion years, Andromeda might swallow the Milky Way whole and end life if it continued till then.
3. Black Holes: We all know what black holes are. They are sinkholes from where nothing returns once it enters, but on the astronomical scale. If earth were to fall into a black hole, we would be pulled apart, a process known as spaghettification, and time would stop. Luckily the nearest black hole is 27000 light years away. But, there is always a possibility that we have not yet recorded the existence of more black holes closer to us. So, we never know when we might fall into galactic vacuum cleaners and die.
4. Gamma ray bursts: As dangerous as black holes are while they exist, their birth can also cause a lot of chaos and destruction. Black holes can form when a very large star goes supernova and releases a humongous amount of energy in two beams. This energy release is known as a gamma ray burst and contain as much energy as the Sun would emit in a billion years. If such a burst were to hit us, Earth would literally be fried. The Milky Way has 400 billion stars and if even one of them released a gamma ray burst, all the planets in the galaxy would be burned.
5. Meteorite impact: We all know about the meteorite that killed all the dinosaurs on Earth. But that was not the first meteorite to strike the Earth. Between 4 billion- 3 billion BC, the earth was hit by 5000 meteorites a day. One meteorite strike, 3.26 billion years ago, was so powerful that scientists believe it caused the earth to shake for half an hour. It is also believed that that collision caused the temperature of the Earth to reach 480 degrees Celsius and caused the oceans to boil. Even smaller impacts can cause destruction on an unimaginable scale. In 1908, a comet only 60 metres wide uprooted 2000 square kilometres of forest. Scientists have estimated that a meteorite with 100 times the energy of the Hiroshima bomb is heading for the Earth and might collide by 2030. Humans are completely unprepared to stop a surprise meteorite strike and even a few months notice might not be enough.
6. Cosmic radiation: Many people don't know this but the Universe tries to irradiate us all the time. Radiation from everywhere bombard the Earth but cause minimal damage to us. That is due to the ozone layer. The ozone layer is our only defence against cosmic radiation and the ultraviolet rays of the Sun. If the ozone layer were to become too thin then scientists estimate that cases of skin cancer and radiation poisoning would skyrocket. If the ozone layer would get completely depleted then staying outside for 5 minutes would be enough to give anyone skin cancer, cause blindness and ultimately kill due to radiation poisoning.
7. Coronal Mass Ejection: In 1859, a blinding flash of light was seen in the sky. Soon after all telegraph systems stopped working in Europe and North America. We now know that the flash of light was a coronal mass ejection (CME) which is a sudden emission of energy by the Sun. CMEs cause problems in our technology. They mess with all kinds of electromagnetic systems. Had the 1859 solar flare occurred now all electrical systems would have just shut down. Traffic lights would stop working, causing jams and accidents. Any place which depends on electricity for its water supply would have no water. Riots would break out and the world would plunge into a state of mass hysteria and anarchy. A solar flare of this magnitude almost happened in 2012. The flare missed us by a week. Had it actually hit Earth, we would have been kicked back to the Stone Age. Scientists estimate the probability of solar flares hitting us in the next decade at 12%, which is quite high.
8. Vacuum Metastability Event: Quantum mechanics might seem boring or extremely difficult and drab compared to the overwhelming event like black hole mergers. On the contrary, quantum mechanics can be equally terrifying. The False Vacuum theory theorizes that the Universe exists in a false vacuum state, that is, not actively decaying but not completely stable either. It is completely possible that the Universe after a long time would move on to a more stable state, ie, complete vacuum. If that were to happen then the entire Universe would just be vacuum and nothing would exist at all. This phenomenon is the vacuum metastability event.
9. Hypervelocity stars: If you thought rogue planets were bad then prepare to be terrified. Stars can also exit their normal orbit and float randomly throughout space at a very fast speed. Moving at 4000 kilometres per second, hypervelocity stars are impossible to stop. A hypervelocity star as big as the Sun would only need to come within 148 million kilometres of the Earth to burn everything. Ironically, detecting these stars is not as easy as one would think. Scientists estimate that there are 1000 such stars in the Milky Way, but have been able to detect only 16.
10. Magnetars: Magnetars can cause the destruction of Earth even if they aren't in the same galaxy. Magnetars are a type of neutron star with extremely string magnetic fields (the strongest in our Universe). Magnetars are prone to star-quakes (earthquakes happening on stars). These quakes lead to the release of a massive amount of gamma rays and X-rays. In 1979, the USSR and NASA said that their satellites around Earth were overwhelmed by a huge dosage of gamma rays. Years later it was found that this energy release was by a magnetar 165000 light years away. Despite the distance, this emission was a 100 times stronger than any gamma ray burst ever recorded. A magnetar needs to be 10 light years away to completely wipe out our ozone layer and leave us to be cooked by the Sun and be garnished with cosmic radiation.