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Thread: Big Bang, CMB and Edwin Hubble

  1. #1 Big Bang, CMB and Edwin Hubble 
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    Hi, I'm trying to see if I have fully answered the questions of the following, any help would be appreciated:

    1.
    Question:
    What does Hubble’s law predict about the speed of a galaxy far away from the Milky Way compared to one that is closer?
    My Answer:
    Hubble's law predicted that the further away the galaxies were from the Milky Way, the larger the redshift and the faster apart they move; the speed of the galaxy is proportional to its distance.

    2.
    Question: In a few sentences, describe Hubble’s two major findings about the spiral nebulae and explain how they led to the development of the Big Bang theory.
    My Answer:
    Hubble noticed that there are other galaxies moving away from Earth. In other terms, the universe is expanding along with the rate of expansion therefore, the universe was smaller and hotter which means that there's a point where the universe began and that led to the big bang theory.

    3.
    Question:
    List two ways that the measured characteristics of cosmic background radiation provide strong evidence in support of the Big Bang theory and explain how each one is used in support.
    My Answer:
    The Big Bang model predicted the existence of the CMB (Cosmic Microwave Background radiation); it basically predicted that the universe gets colder and should be filled w/ radiation (remnant 'leftover' heat from the Big Bang). Theoretical predictions from the Big Bang proposed that the early variation of CMB should show a very specific pattern of tiny differences in temperature between regions of space (Anistropies) which measured at 100 uk (above/below avg. of 2.73 K) therefore nearing with the temperature of deep space (2.7 K). The temperature from the early universe (CMB) matches the predictions from the Big Bang-some even called it 'the Birth of the universe'. Thank you for all the help, in advance.


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  3. #2  
    Brassica oleracea Strange's Avatar
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    On the CMB, I would add something about it being a black body spectrum. But apart from that it looks like a reasonable summary, to me.


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  4. #3  
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    Quote Originally Posted by Jones2341 View Post
    Hi, I'm trying to see if I have fully answered the questions of the following, any help would be appreciated:

    1.
    Question:
    What does Hubble’s law predict about the speed of a galaxy far away from the Milky Way compared to one that is closer?
    My Answer:
    Hubble's law predicted that the further away the galaxies were from the Milky Way, the larger the redshift and the faster apart they move; the speed of the galaxy is proportional to its distance.

    2.
    Question: In a few sentences, describe Hubble’s two major findings about the spiral nebulae and explain how they led to the development of the Big Bang theory.
    My Answer:
    Hubble noticed that there are other galaxies moving away from Earth. In other terms, the universe is expanding along with the rate of expansion therefore, the universe was smaller and hotter which means that there's a point where the universe began and that led to the big bang theory.

    3.
    Question:
    List two ways that the measured characteristics of cosmic background radiation provide strong evidence in support of the Big Bang theory and explain how each one is used in support.
    My Answer:
    The Big Bang model predicted the existence of the CMB (Cosmic Microwave Background radiation); it basically predicted that the universe gets colder and should be filled w/ radiation (remnant 'leftover' heat from the Big Bang). Theoretical predictions from the Big Bang proposed that the early variation of CMB should show a very specific pattern of tiny differences in temperature between regions of space (Anistropies) which measured at 100 uk (above/below avg. of 2.73 K) therefore nearing with the temperature of deep space (2.7 K). The temperature from the early universe (CMB) matches the predictions from the Big Bang-some even called it 'the Birth of the universe'. Thank you for all the help, in advance.
    I agree the first two look pretty good, but I'm not sure I'd express the 3rd quite as you have done. I think I'd be tempted to turn it round and say the discovery of microwave radiation that was (a) isotropic and ( b ), as Strange says, a black body distribution, was something that could not readily be explained except as a radiation "echo" from a very hot and homogeneous early universe that had cooled as a result of Hubble expansion.
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  5. #4  
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    Quote Originally Posted by Strange View Post
    On the CMB, I would add something about it being a black body spectrum. But apart from that it looks like a reasonable summary, to me.
    Quote Originally Posted by exchemist View Post

    I agree the first two look pretty good, but I'm not sure I'd express the 3rd quite as you have done. I think I'd be tempted to turn it round and say the discovery of microwave radiation that was (a) isotropic and ( b ), as Strange says, a black body distribution, was something that could not readily be explained except as a radiation "echo" from a very hot and homogeneous early universe that had cooled as a result of Hubble expansion.
    I'm assuming that it's isotropic because, as Penzias and Wilson found out in 1964, it emitted sound that came from all directions in the sky? However, I don't believe I heard about the black body before; I googled it and it basically told me that black body = spectrum can only be found out through temperature so does it have to do something with "the theoretical predictions of the Big Bang model and how CMB was supposed to show a specific pattern of differences in temperature"?

    Thank you for the help, by the way, I appreciate it
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  6. #5  
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    Quote Originally Posted by Jones2341 View Post
    Quote Originally Posted by Strange View Post
    On the CMB, I would add something about it being a black body spectrum. But apart from that it looks like a reasonable summary, to me.
    Quote Originally Posted by exchemist View Post

    I agree the first two look pretty good, but I'm not sure I'd express the 3rd quite as you have done. I think I'd be tempted to turn it round and say the discovery of microwave radiation that was (a) isotropic and ( b ), as Strange says, a black body distribution, was something that could not readily be explained except as a radiation "echo" from a very hot and homogeneous early universe that had cooled as a result of Hubble expansion.
    I'm assuming that it's isotropic because, as Penzias and Wilson found out in 1964, it emitted sound that came from all directions in the sky? However, I don't believe I heard about the black body before; I googled it and it basically told me that black body = spectrum can only be found out through temperature so does it have to do something with "the theoretical predictions of the Big Bang model and how CMB was supposed to show a specific pattern of differences in temperature"?

    Thank you for the help, by the way, I appreciate it
    Yes, isotropic means the same throughout (Greek: isos = same; tropos = way, manner, character). It meant it could not be something given off by galaxies or other astronomical objects: it had to be from some source, back in time, that was uniform (or almost so) throughout space. But don't forget it is electromagnetic radiation, NOT "sound": in space, no one can hear you scream, remember? We rather lazily use the word "echo", as it is waves remaining from a past event. But they are light waves, stretched out by the expansion of the universe since that time, so that now they are microwaves.

    Regarding "black bodies", any physical body emits electromagnetic radiation due to its temperature. This EM radiation consists of a wide range of different wavelengths. As I expect you are aware, different wavelengths of light have different colours. This is because there are molecules or atoms in the object that preferentially absorb or emit certain wavelengths, compared to others. A "black body" in physics refers to a body that has no particular colour, and thus emits a range of wavelengths determined by its temperature only.

    If you plot radiation intensity vs. wavelength for a black body, you get a kind of asymmetrical bell curve, with a characteristic shape. Black body radiation is thus distinctive and immediately recognisable if you analyse its spectrum (i.e. the intensity of emission at each wavelength). What is more, from the wavelength at which the maximum radiation occurs - the peak of the curve - you can work out the temperature of the emitting object. What the researchers found was that the curve of the CMBR is consistent with emission from an object at 2.7K.....but this "object" was the whole sky!
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  7. #6  
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    So can I say that:
    1. In 1964, Penzias and Wilson discovered a sound that seemed to be isotropic (coming from all directions of the sky). It turned out to be the remnants of the Big Bang echo, and evidence that at the point of singularity occurred an explosion that released all the clumps of matter and gave birth to the universe.
    2. The researchers found that the maximum radiation point of the CMB was at a temperature of 2.73 K (below/above absolute zero) and it surrounded the whole sky. This provided evidence for the Big Bang because the temperatures of the early universe matches predictions from the Big Bang.
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  8. #7  
    Brassica oleracea Strange's Avatar
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    Rather than "maximum radiation point" I would say something like "the spectrum was equivalent to a temperature of 2.73 K"

    The fact it is a black body spectrum is important because that would be generated by a uniform plasma at the expected temperature. But if this is not something you have not covered (I assume this is some sort of course work?) and are not confident talking about, then I think you can leave it out.
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  9. #8  
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    Quote Originally Posted by Strange View Post
    Rather than "maximum radiation point" I would say something like "the spectrum was equivalent to a temperature of 2.73 K"

    The fact it is a black body spectrum is important because that would be generated by a uniform plasma at the expected temperature. But if this is not something you have not covered (I assume this is some sort of course work?) and are not confident talking about, then I think you can leave it out.
    Yes, it's ILC...but I guess I understand it.
    2. There was a question about why the CMB was uniform even though there were clumps of matter (e.g. Galaxies, stars, other planets) in the universe and so it didn't make sense for the CMB to be uniform. Theoretical predictions of the Big Bang model proposed that the CMB had a very specific pattern, or unique characteristic, in temperature between regions of space. It was discovered that the spectrum of the CMB was equivalent to the temperature of 2.73 K (below/above absolute zero, keeping in mind that deep space's temperature is 2.7 K). This is called the black body distribution, which proves/acts as evidence to the Big Bang because the temperatures of the early universe matches the predictions from the Big Bang.
    Am I right?
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  10. #9  
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    Quote Originally Posted by Jones2341 View Post
    So can I say that:
    1. In 1964, Penzias and Wilson discovered a sound that seemed to be isotropic (coming from all directions of the sky). It turned out to be the remnants of the Big Bang echo, and evidence that at the point of singularity occurred an explosion that released all the clumps of matter and gave birth to the universe.
    2. The researchers found that the maximum radiation point of the CMB was at a temperature of 2.73 K (below/above absolute zero) and it surrounded the whole sky. This provided evidence for the Big Bang because the temperatures of the early universe matches predictions from the Big Bang.
    As Strange says, the radiation distribution corresponds to that of a back body at 2.7K (has to be ABOVE zero as nothing can ever be below 0K by definition).

    It doesn't "surround the whole sky" - nothing surrounds the sky, obviously. It comes from the whole sky, i.e. comes from all directions in space equally.

    Otherwise fine.

    You might want to take a look at the graph here of black body radiation: http://quantumfreak.com/wp-content/u...ion-curves.png
    This shows how the peak wavelength changes as the temperature of the emitting body changes. In fact of course the whole distribution moves to shorter wavelengths as the temperature of the body goes up. But looking at what happens to the peak is one simple indicator.
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  11. #10  
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    Thank you for your help, strange and exchemist; I appreciate it
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