What is universe

It would take a modern jet fighter more than a million years to reach the nearest star to the Sun. Travelling at the speed of light , km per second , it would take , years to cross our Milky Way galaxy alone.

No one knows the exact size of the Universe, because we cannot see the edge — if there is one. All we do know is that the visible Universe is at least 93 billion light years across. A light year is the distance light travels in one year — about 9 trillion km. The Universe has not always been the same size. Along with asteroids and comets, the planets orbit the Sun. The Sun is one among hundreds of billions of stars in the Milky Way galaxy, and most of those stars have their own planets, known as exoplanets.

The Milky Way is but one of billions of galaxies in the observable universe — all of them, including our own, are thought to have supermassive black holes at their centers. It is, simply, everything.

Though the universe may seem a strange place, it is not a distant one. Wherever you are right now, outer space is only 62 miles kilometers away. About 8, miles 12, kilometers below your feet — on the opposite side of Earth — lurks the unforgiving vacuum and radiation of outer space.

It just so happens that things live here and the environment near the surface of this particular planet is hospitable for life as we know it. Earth is a tiny, fragile exception in the cosmos. For humans and the other things living on our planet, practically the entire cosmos is a hostile and merciless environment.

Our planet, Earth, is an oasis not only in space, but in time. It may feel permanent, but the entire planet is a fleeting thing in the lifespan of the universe. For nearly two-thirds of the time since the universe began, Earth did not even exist. Nor will it last forever in its current state. It might even expand large enough to swallow Earth itself.

After all, humans have only just begun deciphering the cosmos. While the distant future is difficult to accurately predict, the distant past is slightly less so. By studying the radioactive decay of isotopes on Earth and in asteroids, scientists have learned that our planet and the solar system formed around 4. The universe, on the other hand, appears to be about Scientists arrived at that number by measuring the ages of the oldest stars and the rate at which the universe expands. They also measured the expansion by observing the Doppler shift in light from galaxies, almost all of which are traveling away from us and from each other.

In the distant future, the galaxies will be so far away that their light will not be visible from Earth. Put another way, the matter, energy and everything in the universe including space itself was more compact last Saturday than it is today.

The same can be said about any time in the past — last year, a million years ago, a billion years ago. A bit farther back in time, everything was in the same spot. Or really the entire universe not just the matter in it was one spot.

Don't spend too much time considering a mission to visit the spot where the universe was born, though, as a person cannot visit the place where the Big Bang happened.

It's not that the universe was a dark, empty space and an explosion happened in it from which all matter sprang forth. Time, too, began with the big bang.

Space itself expanded from a single point to the enormous cosmos as the universe expanded over time. The universe contains all the energy and matter there is. Much of the observable matter in the universe takes the form of individual atoms of hydrogen, which is the simplest atomic element, made of only a proton and an electron if the atom also contains a neutron, it is instead called deuterium.

While Stephen Hawking keeps changing his mind, the popular definition of a black hole is a region of space-time so dense that, past a certain point, nothing can escape its gravitational pull. Black holes are born when dense packets of matter collapse in on themselves, such as during the deaths of especially hefty stars.

Some versions of the equations that describe black holes go on to say that the compressed matter does not fully collapse into a point—or singularity—but instead bounces back, spewing out hot, scrambled matter. Poplawski crunched the numbers and found that observations of the shape and composition of the universe match the mathematical picture of a black hole being born.

The initial collapse would equal the big bang, and everything in and around us would be made from the cooled, rearranged components of that scrambled matter. Even better, the theory suggests that all the black holes in our universe may themselves be the gateways to alternate realities. So how do we test it? This model is based on black holes that spin, because that rotation is part of what prevents the original matter from fully collapsing.

Another cosmic puzzle comes up when you consider what happened in the first slivers of a second after the big bang. Maps of relic light emitted shortly after the universe was born tell us that baby space-time grew exponentially in the blink of an eye before settling into a more sedate rate of expansion. This process, called inflation, is pretty popular among cosmologists, and it got a further boost this year with the potential but still unconfirmed discovery of ripples in space-time called gravitational waves , which would have been products of the rapid growth spurt.

If inflation is confirmed, some theorists would argue that we must live in a frothy sea of multiple universes. To reach a stable state, the vacuum began to bubble like a pot of boiling water.

With each bubble, a new universe was born, giving rise to an endless multiverse. One option, then, is to look for any evidence of our bubble universe colliding with another. Or it could be a statistical fluke.