When you are looking at the sky, you can see a lots of starts shining. But as you see them, you are actually looking at the past, not the present. Sounds confusing. isn't it?
How is it possible?
Light have a very definite speed that is 186,282 miles per second( 299,792,458 meters per second ).
Our sun is 93,020,000 miles (149,600,000 km) away from earth and it takes 8 minutes and 18 seconds for light to reach us from the sun. The average distance of Pluto from Sun is 3,600,000,000,000 miles( 5,906,376,272 km ). It takes an average of about 5 hours and 30 minutes, for the light from sun to reach Pluto. It takes about 3 minutes for light from sun to reach mercury.
So as the numbers became huge, it was no loner possible to calculate distances of cosmic objects in miles or kilometers. So 'light year' was introduced.
1 light year is the distance covered by light in vacuum in one Julian year. The distance traveled would be about 6 trillion miles ( just under 10 trillion kilometers ). Still cosmic objects are so far away that we use millions and billions of lights year to represent their distance.
So my point is, as light from sun travels for just over 8 minutes to reach earth, so when we see the sun, we always see it 8 minutes older from it's current state.
Just try to imagine, let's just build a super-strong watch and put is so close to the sun, that the light from the sun would take no time to reach it and it also act as a photo detector or a light detector. Let's have the copy of that watch on earth.
One day you are looking at the sky and suddenly the sun vanished.(just imagine). So you call your lazy friend, who is always sleeping and told him that hey dude, you know what happened. you wouldn't believe it. At 10.30 today, the aliens stole our sun and i saw them with my naked eyes.( ha ha ha ).
One day you are looking at the sky and suddenly the sun vanished.(just imagine). So you call your lazy friend, who is always sleeping and told him that hey dude, you know what happened. you wouldn't believe it. At 10.30 today, the aliens stole our sun and i saw them with my naked eyes.( ha ha ha ).
Actually the the sun vanished at 10.22 approximately. after 8 minutes we knew that the sun is gone. So if we check the super-strong watches for last photon captured or light captured, then the one close to the sun will read last photon captured at 10.22 and the one on earth would read 10.30 because the photons takes 8 minutes to go from sun to earth so the last photon from sun will take 8 mins to reach earth. After that suddenly the light or photons will stop coming, resulting darkness everywhere. So we would know the sun is gone only after 8 minutes.
So when you are looking out into space, it's just like looking into the past or looking back into time.
Andromeda is nearest spiral galaxy to our milky way, it is approximately 2.5 million light years from earth. So it would take 2.5 million years for the light from Andromeda to reach earth. There are billions and billions of galaxies with trillions and trillions of stars out there and these spread across 13.7 billion years back in time. So light from the 1st stars should be traveling for billions of years.
What is cosmic microwave background(CMB)?
In fact the 1st light or photons started their journey after about 380,000 after the 'big bang'. We can still see this radiation today, uniformly all over the sky. It is called the 'cosmic microwave background'.
It is called 'cosmic microwave background' because the 1st photons have been traveling for billions of years to reach us. So no matter at what energy they have started their journey, eventually over time they loose their energy to fall into the 'microwave' spectrum of electromagnetic radiation.
The existence of cosmic microwave background radiation was 1st predicted by Ralph Alpher, Robert Herman and George Gamow in 1948, as part of their work on Big Bang Nucleosynthesis. It was first observed inadvertently in 1965 by Arno Penzias and Robert Wilson at the Bell Telephone Laboratories in Murray Hill, New Jersey. The radiation was acting as a source of excess noise in a radio receiver they were building. No matter what they do, the radiation never got away. Coincidentally, researchers at nearby Princeton University, led by Robert Dicke and including Dave Wilkinson of the WMAP science team, were devising an experiment to find the CMB. When they heard about the Bell Labs result they immediately realized that the CMB had been found.
How CMB works?
In the early stages of the universe after the 'big bang', it was just a hot and dense primordial soup of sub-atomic particles or photon-baryon battleground which we could say shaped everything in our universe. So early universe was filled with radiation and plasma in short. In fact it was so hot and energetic that the electrons couldn't stick to the atoms. High speed interactions of those particles, photons constantly interacting with electrons and moving with very very high speeds both of them, unstable and unimaginable environment. So of course the so called CMB photons were trapped inside that plasma due to the tight coupling of photons and charged baryons. Until after 380,000 years the as the universe was expanding, tempreture of the plasma were cooled enough, below 3000k for neutral hydrogen atoms to be formed. And that is when the photons were free to move out, that was the time when the radiation 'decoupled' from matter.
The CMB has the spectrum of a blackbody. A blackbody spectrum is produced by an isothermal, opaque and non-reflecting object. The CMB photons as they travel through the expanding universe, their wavelength expands so today CMB is a faint glow in the microwave spectrum of radiation which shines at 2.725K today.
The CMB radiation consists of tiny fluctuations in tempretures as mapped by COBE and WMAP satellites. These fluctuations are the density fluctuations which is then magnified by gravity to form the universe as we see today. Where the density was more, those were the regions the galaxy and galaxy clusters were formed.
This is the proof that 'big bang' exists. It is the answer to questions like how our universe is shaped and why it is like this. It's the 'Holy-Grail of cosmology' itself. As George Smoot would say it as "it's like looking at the face of god'. It should be as it shows the very beginning of the universe. We could know how everything was put together only after few thousand years after the big bang.
They say that the art of an artist is the reflection of his/her inner-self. So if you believe in god and believe that the almighty created the universe himself then you could see 'him' through his handy work of building the universe from the very beginning.
To get more info, please visit - arxiv.org
So when you are looking out into space, it's just like looking into the past or looking back into time.
Andromeda is nearest spiral galaxy to our milky way, it is approximately 2.5 million light years from earth. So it would take 2.5 million years for the light from Andromeda to reach earth. There are billions and billions of galaxies with trillions and trillions of stars out there and these spread across 13.7 billion years back in time. So light from the 1st stars should be traveling for billions of years.
What is cosmic microwave background(CMB)?
In fact the 1st light or photons started their journey after about 380,000 after the 'big bang'. We can still see this radiation today, uniformly all over the sky. It is called the 'cosmic microwave background'.
It is called 'cosmic microwave background' because the 1st photons have been traveling for billions of years to reach us. So no matter at what energy they have started their journey, eventually over time they loose their energy to fall into the 'microwave' spectrum of electromagnetic radiation.
The existence of cosmic microwave background radiation was 1st predicted by Ralph Alpher, Robert Herman and George Gamow in 1948, as part of their work on Big Bang Nucleosynthesis. It was first observed inadvertently in 1965 by Arno Penzias and Robert Wilson at the Bell Telephone Laboratories in Murray Hill, New Jersey. The radiation was acting as a source of excess noise in a radio receiver they were building. No matter what they do, the radiation never got away. Coincidentally, researchers at nearby Princeton University, led by Robert Dicke and including Dave Wilkinson of the WMAP science team, were devising an experiment to find the CMB. When they heard about the Bell Labs result they immediately realized that the CMB had been found.
How CMB works?
In the early stages of the universe after the 'big bang', it was just a hot and dense primordial soup of sub-atomic particles or photon-baryon battleground which we could say shaped everything in our universe. So early universe was filled with radiation and plasma in short. In fact it was so hot and energetic that the electrons couldn't stick to the atoms. High speed interactions of those particles, photons constantly interacting with electrons and moving with very very high speeds both of them, unstable and unimaginable environment. So of course the so called CMB photons were trapped inside that plasma due to the tight coupling of photons and charged baryons. Until after 380,000 years the as the universe was expanding, tempreture of the plasma were cooled enough, below 3000k for neutral hydrogen atoms to be formed. And that is when the photons were free to move out, that was the time when the radiation 'decoupled' from matter.
The CMB has the spectrum of a blackbody. A blackbody spectrum is produced by an isothermal, opaque and non-reflecting object. The CMB photons as they travel through the expanding universe, their wavelength expands so today CMB is a faint glow in the microwave spectrum of radiation which shines at 2.725K today.
The CMB radiation consists of tiny fluctuations in tempretures as mapped by COBE and WMAP satellites. These fluctuations are the density fluctuations which is then magnified by gravity to form the universe as we see today. Where the density was more, those were the regions the galaxy and galaxy clusters were formed.
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| Nine Year Microwave Sky The detailed, all-sky picture of the infant universe created from seven years of WMAP data. The image reveals 13.77 billion year old temperature fluctuations (shown as color differences) that correspond to the seeds that grew to become the galaxies. The signal from the our Galaxy was subtracted using the multi-frequency data. This image shows a temperature range of ± 200 microKelvin. |
This is the proof that 'big bang' exists. It is the answer to questions like how our universe is shaped and why it is like this. It's the 'Holy-Grail of cosmology' itself. As George Smoot would say it as "it's like looking at the face of god'. It should be as it shows the very beginning of the universe. We could know how everything was put together only after few thousand years after the big bang.
They say that the art of an artist is the reflection of his/her inner-self. So if you believe in god and believe that the almighty created the universe himself then you could see 'him' through his handy work of building the universe from the very beginning.
To get more info, please visit - arxiv.org
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