kmguru
Staff member
Saw on the net:
What does the word "universe" mean?
The "observable universe," Sweitzer explained, "is the one astrophysicists generally talk about because it's the one open to empirical measurements. In fact it's the only one we can or ever will be able to talk with any certainty about."
He goes on to explain that "universe" (sans the word "observable") is a larger concept that scientists think "conforms to our laws of physics and all the assumptions that go with them." Comprehending this universe, Sweitzer said, "requires a leap of faith into unobservable realms."
Finally, there is "the Universe," which, by virtue of its capital "U," includes "absolutely everything, even possibilities of dimensions, modes and regions that obey laws of physics we don't know or maybe even can't know."
Okay then. If we can't know it, let's move on to the next question.
How did the universe begin?
There is a very simple answer to this question: We don't know. And we may never know.
The leading theory for the formation of our universe is the Big Bang, of course. According to this theory, all the matter and energy in our present observable universe was compressed into a very small area, before, in a nanosecond, it exploded outward and expanded continually until the present time -- and will perhaps do so forever.
Unimaginable as it might seem, the Big Bang theory is tame compared to some recently emerging wilder ideas, speculations that pop up like parallel universes in a vacuum of understanding.
Some cosmologists say our observable universe is one of many that spring forth continually from a series of bubbles. In this scenario, one Big Bang begets another.
Another recently proposed scenario holds that instead of springing forth in a violent instant from a teensy point in space, our universe was created when two parallel membranes collided. These "branes," as theorists call them, would have floated like sheets of paper through a fifth dimension until slamming together and generating energy and heat that led to the same expansion described by traditional Big Bang theory.
This Ekpyrotic Universe theory, as it is called, does not replace Big Bang theory. Instead, it offers an alternative way that the currently observed expansion might have been jump-started.
In any case, the Big Bang theory does not actually explain how the universe began. It assumes that space, time and energy already existed. Accept that rather significant caveat and one can then discuss the leading theory for how our present observable universe came into being.
"It started from an extraordinarily dense and hot state, and it has been expanding ever since," said Livio, of the Space Telescope Science Institute, giving perhaps the world's most concise definition of the Big Bang model. But there's more to point out here, including the fact that "dense" is rather an understatement.
Everything that exists now, at least in the observable universe, was once all packed into a sphere one millionth of a meter across, Sweitzer said. Translation -- too small to see.
"That may seem pretty small, but it's only because of our human perspective," Sweitzer assured us, adding that today's universe is "extraordinarily empty." Imagine, as an example, that the area of our solar system -- with nine planets packed into a region less than 9 billion miles (14.5 billion kilometers) across -- is relatively crowded compared to the vast empty stretches between stars, where nothing but a few molecules hang out.
ref: science.com
What does the word "universe" mean?
The "observable universe," Sweitzer explained, "is the one astrophysicists generally talk about because it's the one open to empirical measurements. In fact it's the only one we can or ever will be able to talk with any certainty about."
He goes on to explain that "universe" (sans the word "observable") is a larger concept that scientists think "conforms to our laws of physics and all the assumptions that go with them." Comprehending this universe, Sweitzer said, "requires a leap of faith into unobservable realms."
Finally, there is "the Universe," which, by virtue of its capital "U," includes "absolutely everything, even possibilities of dimensions, modes and regions that obey laws of physics we don't know or maybe even can't know."
Okay then. If we can't know it, let's move on to the next question.
How did the universe begin?
There is a very simple answer to this question: We don't know. And we may never know.
The leading theory for the formation of our universe is the Big Bang, of course. According to this theory, all the matter and energy in our present observable universe was compressed into a very small area, before, in a nanosecond, it exploded outward and expanded continually until the present time -- and will perhaps do so forever.
Unimaginable as it might seem, the Big Bang theory is tame compared to some recently emerging wilder ideas, speculations that pop up like parallel universes in a vacuum of understanding.
Some cosmologists say our observable universe is one of many that spring forth continually from a series of bubbles. In this scenario, one Big Bang begets another.
Another recently proposed scenario holds that instead of springing forth in a violent instant from a teensy point in space, our universe was created when two parallel membranes collided. These "branes," as theorists call them, would have floated like sheets of paper through a fifth dimension until slamming together and generating energy and heat that led to the same expansion described by traditional Big Bang theory.
This Ekpyrotic Universe theory, as it is called, does not replace Big Bang theory. Instead, it offers an alternative way that the currently observed expansion might have been jump-started.
In any case, the Big Bang theory does not actually explain how the universe began. It assumes that space, time and energy already existed. Accept that rather significant caveat and one can then discuss the leading theory for how our present observable universe came into being.
"It started from an extraordinarily dense and hot state, and it has been expanding ever since," said Livio, of the Space Telescope Science Institute, giving perhaps the world's most concise definition of the Big Bang model. But there's more to point out here, including the fact that "dense" is rather an understatement.
Everything that exists now, at least in the observable universe, was once all packed into a sphere one millionth of a meter across, Sweitzer said. Translation -- too small to see.
"That may seem pretty small, but it's only because of our human perspective," Sweitzer assured us, adding that today's universe is "extraordinarily empty." Imagine, as an example, that the area of our solar system -- with nine planets packed into a region less than 9 billion miles (14.5 billion kilometers) across -- is relatively crowded compared to the vast empty stretches between stars, where nothing but a few molecules hang out.
ref: science.com
