How did the universe begin?

One of the most interesting questions considered by astrophysicists deals with the start of our universe. Indeed, there is a great deal of speculation on the subject, with different theories about how the universe began, and what may have existed before the universe came into being. 

 Science has advanced to the point where we can infer something about the entire universe. This has been a great challenge considering how unimaginably vast the universe is. The countless stars you see in the darkest sky constitute merely 3000 neighbors out of about 300,000,000,000 stars in our galaxy, and as many as 100,000,000,000 galaxies exist in the universe. Humans have always wondered: Has the universe always existed like we see it now, or did it somehow start all of a sudden? In the beginning of this past century, we found out in amazement that the entire universe is expanding. This led physicists to deduce that the universe started out in the finite past with a minuscule size. Realizing that the universe had a beginning, and awed by its vastness and its creations, people have asked: How did the universe begin? After all, we are here to be amazed by it because the universe eventually created lives like us. Now, after decades of observing and thinking, we have come to answer confidently the question of the origin of our universe... with what is known as the "big bang".   

What is the Big Bang?

According to the big bang theory, the universe began by expanding from an infinitesimal volume with extremely high density and temperature. The universe was initially significantly smaller than even a pore on your skin. With the big bang, the fabric of space itself began expanding like the surface of an inflating balloon – matter simply rode along the stretching space like dust on the balloon's surface. The big bang is not like an explosion of matter in otherwise empty space; rather, space itself began with the big bang and carried matter with it as it expanded. Physicists think that even time began with the big bang. Today, just about every scientist believes in the big bang model. The evidence is overwhelming enough that in 1951, the Catholic Church officially pronounced the big bang model to be in accordance with the Bible.

Until the early 1900s, most people had assumed that the universe was fixed in size. New possibilities opened up in 1915, when Einstein formulated his famous general relativity theory that describes the nature of space, time, and gravity. This theory allows for expansion or contraction of the fabric of space. In 1917, astronomer Willem de Sitter applied this theory to the entire universe and boldly went on to show that the universe could be expanding. Aleksandr Friedmann, a mathematician, reached the same conclusion in a more general way in 1922, as did Georges Lemaître, a cosmologist and a Jesuit, in 1927. This step was revolutionary since the accepted view at the time was that the universe was static in size. Tracing back this expanding universe, Lemaître imagined all matter initially contained in a tiny universe and then exploding. These thoughts introduced amazing new possibilities for the universe, but were independent of observation at that time.

Why Do We Think the Big Bang Happened?

Three main observational results over the past century led astronomers to become certain that the universe began with the big bang. First, they found out that the universe is expanding—meaning that the separations between galaxies are becoming larger and larger. This led them to deduce that everything used to be extremely close together before some kind of explosion. Second, the big bang perfectly explains the abundance of helium and other nuclei like deuterium (an isotope of hydrogen) in the universe. A hot, dense, and expanding environment at the beginning could produce these nuclei in the abundance we observe today. Third, astronomers could actually observe the cosmic background radiation—the afterglow of the explosion—from every direction in the universe. This last evidence so conclusively confirmed the theory of the universe's beginning that Stephen Hawking said, "It is the discovery of the century, if not of all time."

Expansion of Universe -

Around the same time that people began to come up with the idea of an expanding universe, astronomer Vesto Slipher noticed that there are more galaxies going away from us than approaching us. Astronomers know that a galaxy is approaching or receding by looking at the spectrum of its light. If the spectrum is shifted toward shorter wavelength (blueshift), then the galaxy must be approaching, just like the sound of an approaching racing car has a higher pitch (shorter sound wavelength). If the spectrum is shifted toward longer wavelength (redshift), then the galaxy must be receding, just like the sound of a racing car that has passed us has a lower pitch (longer sound wavelength). The degree of the shift depends on the speed of approach or recession. So in other words, Slipher observed more galaxies whose spectrum was redshifted than those whose spectrum was blueshifted.

In 1929, Edwin Hubble discovered that farther galaxies are going away from us at higher speeds, proportional to their distance. In other words, the spectra of more distant galaxies had higher redshifts. From distant galaxies, light takes millions or even billions of years to reach us. This means we are seeing an image from millions or billions of years ago. In redshift, the spectrum is shifted from shorter wavelength to longer wavelength as the light travels from the galaxy to us. This increase in wavelength is due to expansion of the very fabric of space itself over the years that the light was traveling. If the wavelength had doubled, space must have expanded by a factor of two. Thus, Hubble's discovery was that this expansion factor was roughly proportional to the distance light traveled, or equivalently, to how far back in time you looked. This means that the universe was smaller and smaller earlier and earlier. The universe has been expanding.

Conclusion -

The 20^th century saw a giant leap in how humans perceive the cosmos. No longer did people assume that the universe was static in size. By looking at how distant galaxies recede from us, we learned instead that the universe is expanding in volume. Tracing the expanding universe backward in time, we imagined a dense, hot beginning of our universe in a finite past. In the middle of the century, we found out that the nuclear reactions in this hot early universe accurately account for the previously mysterious abundance of helium and deuterium. Moreover, we detected a faint afterglow of the big bang that occurred billions of years ago. That the universe began with a big bang is essentially conclusive and may stand as the most profound discovery humans have ever made.

The big bang, however, is merely a global description of the origin of the universe. Today, particle physicists have consistent theories about the history of the universe down to only a trillionth of a second after its birth or even earlier. They can test their theories experimentally with particle accelerators that can simulate events involving enormous energies similar to the condition at the beginning. To learn more about how exactly the universe began, physicists must develop a theory that works at even earlier times after the big bang. Such theory must combine both the general relativity (because of the extreme gravitational field at the beginning) and quantum mechanics (because of the extreme compactness of the universe at the beginning). The goal of physics today is to develop this quantum theory of gravity so that we may one day understand what exactly happened around the moment of the big bang to get the universe started.

Read More...

Why Do Stars Twinkle?

Head outside on a nice dark, clear night and look up. If you’re away from the glare of the city lights, you should be able to see lots of stars. But if you notice, the stars seem to be twinkling. What’s going, why do stars twinkle?

 If you could fly up into space and do the same experiment, you wouldn’t see the stars twinkle at all. They would be unchanging points of light in all directions. Something’s changed from when you were on the surface of the Earth to when you were in space. That thing is the Earth’s atmosphere.Stars twinkle because of turbulence in the Earth’s atmosphere.

Light from distant stars passes through various layers in the Earth’s atmosphere, and it gets refracted depending on the temperature and density of the air at that point. So light will pass through one layer, be refracted at one angle, and then pass through a different layer and be refracted at a different angle. When you see a twinkling star, you’re seeing the accumulated refractions from all those layers, which change the position and size of the star – many times a second.

This twinkling is a big problem for astronomers, who need the clearest possible view of the sky. That’s why observatories are built at the top of mountains, where there’s less atmosphere in between the telescope and the vacuum of space. And to have the clearest view, you really want to launch a space telescope that can get above the Earth’s atmosphere and see the stars as they really are.

Read More...

Why Does The Moon Shine?

Have you ever though about why does the moon shine? The fact is that moon is actually very Dark. We should not be able to see it all. Also unlike what the ancients thought the moon does not produce its own light. The answers to these questions are actually very interesting once you think about them. The Moon shines because it actually is a mirror but it a most interesting mirror when you get into it.

The general answer most people know about why the moon shines is that it reflects the light of the Sun. This is basically true. The moon basically bounces or relays sunlight from the Day side of the Earth to it’s night side. This of course alters as it orbits the Earth and gets near the side of Earth where the Sun shines from. This is what makes the moon appear visible

during the Day. The changing of the Moon’s phases is also a result of how we view the light reflected off of the moon. Half of the moon is always lit up by the light of the Sun it is simply that the moon is orbiting us that the amount of that lit portion changes as the month goes by.

The real mystery is why does the moon reflect at all. Like most objects in space, the Moon possesses a reflective characteristic called albedo. Albedo is how well an object reflects light. This characteristic seems pretty straight forward. Material like ice and snow have very reflective albedos. Land and Greenery have very low reflective albedos. What makes the moon so interesting is that it has the same Albedo as coal. That means that it has almost no reflective quality up close. So when the Apollo mission were going on the Moon was actually a pretty dark place. This only makes sense because of the large lava plains that it has.

The reason why the moon still seems so reflective is because of an interesting effect called the opposition effect. The opposition effect basically states that certain types of non reflective surfaces lose their shadows when directly in the line of sight of the light source shining on them. This why a road at night lit by head lights will seem to brighter than it is. The reason that moon does this so well is the loose regolith that covers most of its surface. The opposition effect is strongest for the moon when it is directly in the opposite position of the Sun in relation to the Earth.

Read More...

How big is the universe?

Recent measurements reveal that the Universe is at least 150 billion light-years in diameter. For comparison, its age is estimated to be about 13.7 billion years. Doesn’t make sense does it?

Since some of you may be wondering what kind of disparity we’re talking about, let me elaborate. You see, to arrive at that age, scientists had to measure light (or electromagnetic radiation) coming from the outermost borders of the Universe. This radiation, specifically known as the cosmic microwave background radiation is a throwback to the youngest years of the Universe. So if it had to take 13.7 billion years for light coming from the outermost regions to reach us, then we should be expecting a diameter within that order of magnitude. Simply put, around twice that value or 27.4 billion light-years. But lo and behold, we’re seeing a number much much larger than that.

 This value, however, only makes sense if our Universe’s size were constant. Studies have shown that that isn’t the case. In fact, separate observations have shown that the Universe is actually expanding. To top it all, it is confirmed that it does so at an accelerated rate.

Lets make a very simplified analogy, just to give us a rough idea regarding the source of discrepancy. Imagine yourself having a friend standing on a planet at the outermost galaxy. Lets also assume you both have superhuman strength and are able to play catch with indestructible balls (whose constant speed you both know) that takes a straight path, and that no obstruction exists along the said path.

If he throws a ball, you’d be able to determine either the time of flight or the distance traveled if you knew the other physical quantity. Thus, if the time of flight is 13.7 billion years and the ball was traveling at the speed of light, neglecting relativistic effects, the distance should be 13.7 billion light-years.

But what if your friend is moving towards or away from you? We would have to make certain adjustments. You would still be able to measure the said physical quantities if he were made to throw a good number of balls at regular intervals and if you made some adjustments to your equation, taking into consideration the relative velocities involved.

After the first throw, if your friend is moving away, the distance between you and him would be greater than 13.7 billion years. Even greater distances can be achieved if he were moving away at increasing velocities.

Recent measurements reveal that the Universe is at least 150 billion light-years in diameter. For comparison, its age is estimated to be about 13.7 billion years. Doesn’t make sense does it?

Read more: http://www.universetoday.com/37409/how-big-is-the-universe/#ixzz2DfVrXAIBRecent measurements reveal that the Universe is at least 150 billion light-years in diameter. For comparison, its age is estimated to be about 13.7 billion years. Doesn’t make sense does it?

Since some of you may be wondering what kind of disparity we’re talking about, let me elaborate. You see, to arrive at that age, scientists had to measure light (or electromagnetic radiation) coming from the outermost borders of the Universe. This radiation, specifically known as the cosmic microwave background radiation is a throwback to the youngest years of the Universe. So if it had to take 13.7 billion years for light coming from the outermost regions to reach us, then we should be expecting a diameter within that order of magnitude. Simply put, around twice that value or 27.4 billion light-years. But lo and behold, we’re seeing a number much much larger than that.

Recent measurements reveal that the Universe is at least 150 billion light-years in diameter. For comparison, its age is estimated to be about 13.7 billion years. Doesn’t make sense does it? Since some of you may be wondering what kind of disparity we’re talking about, let me elaborate. You see, to arrive at that age, scientists had to measure light (or electromagnetic radiation) coming from the outermost borders of the Universe. This radiation, specifically known as the cosmic microwave background radiation is a throwback to the youngest years of the Universe. So if it had to take 13.7 billion years for light coming from the outermost regions to reach us, then we should be expecting a diameter within that order of magnitude. Simply put, around twice that value or 27.4 billion light-years. But lo and behold, we’re seeing a number much much larger than that.

Read more: http://www.universetoday.com/37409/how-big-is-the-universe/#ixzz2DfVkSfqq

yRecent measurements reveal that the Universe is at least 150 billion light-years in diameter. For comparison, its age is estimated to be about 13.7 billion years. Doesn’t make sense does it? Since some of you may be wondering what kind of disparity we’re talking about, let me elaborate. You see, to arrive at that age, scientists had to measure light (or electromagnetic radiation) coming from the outermost borders of the Universe. This radiation, specifically known as the cosmic microwave background radiation is a throwback to the youngest years of the Universe. So if it had to take 13.7 billion years for light coming from the outermost regions to reach us, then we should be expecting a diameter within that order of magnitude. Simply put, around twice that value or 27.4 billion light-years. But lo and behold, we’re seeing a number much much larger than that.

Read more: http://www.universetoday.com/37409/how-big-is-the-universe/#ixzz2DfVkSfqq

Recent measurements reveal that the Universe is at least 150 billion light-years in diameter. For comparison, its age is estimated to be about 13.7 billion years. Doesn’t make sense does it? Since some of you may be wondering what kind of disparity we’re talking about, let me elaborate. You see, to arrive at that age, scientists had to measure light (or electromagnetic radiation) coming from the outermost borders of the Universe. This radiation, specifically known as the cosmic microwave background radiation is a throwback to the youngest years of the Universe. So if it had to take 13.7 billion years for light coming from the outermost regions to reach us, then we should be expecting a diameter within that order of magnitude. Simply put, around twice that value or 27.4 billion light-years. But lo and behold, we’re seeing a number much much larger than that.

Read more: http://www.universetoday.com/37409/how-big-is-the-universe/#ixzz2DfVkSfqq

Read More...

Will the universe ever end?

There are 3 major theories concerning how our universe and everything in it will ultimately end up: the Big Crunch, the Big Chill, and the Big Rip.

Firstly, then, let us look at the Big Crunch. This is the theory that states that the Universe will eventually stop expanding and start to collapse in on itself – kind of like running the Big Bang in reverse. Now imagine, if you will, that we’re at the moment of the Big Bang. There’s an immense explosion, and matter, energy, and forces are created almost instantaneously – in the first few nanoseconds of one gigantic Universal cataclysm.

After the Bang, the Universe and all its matter continues to expand outwards for a few billion years or so. However, there is a problem. Between all the bits of matter in the Universe, there is Gravitational Attraction.

And the bigger and closer together two lumps of stuff are, the more attraction there is. So while the force of the Big Bang has thrown matter outwards and further and further apart, gravity is trying to bring it all back inwards and closer together. Now here is the important thing: if the average density of all the matter in the Universe is large enough – more than the so-called Critical Density – then gravity will overcome the force of the initial Bang, and the expansion of the Universe will slow down…then stop…then reverse…then begin to contract at an ever-increasing rate.

Imagine it – as the billions of suns and planets get closer together they heat up, until eventually they all implode into a white-hot singularity. This of course means the end of the Universe as we know it.

On the other hand, if the average density of matter is below the critical density, then gravity is too feeble to overcome the force of the bang, and the Universe just keeps expanding forever.

If this happens, then as the matter gets more and more spread out, it gets colder and colder, until the whole Universe chills to a temperature of absolute zero. So the Universe does not so much end; rather, its contents reach a uniform equilibrium which renders life impossible. This is theory number two, and we call this “The Big Chill”.


Now for most of the 20th century, astronomers knew that the universe was expanding – by measuring the rate that other galaxies seemed to be moving away from us. So this would be consistent with either the Big Crunch (if it was yet to slow down and reverse), or the Big Chill theories.

But it wasn’t until the beginning of the 21st century that they discovered that the Universe that the expansion of the universe was actually speeding up – apparently accelerated by some unknown force, which they christened Dark Energy.

Dark Energy directly opposes the force of gravitational attraction, pulling all the matter in the Universe apart in all directions. If this happens, then gravity will eventually become too weak to hold things together, and everything will be ripped apart at the seams.

First galaxies will be separated from each other, then – a few months before the end – solar systems would rip apart. In the last few minutes, suns and planets follow, and finally – a few nanoseconds before the end of time – even atoms would be destroyed. Ouch. Hence we call this the Big Rip.

Read More...