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Thread: Space travel, and gravity and other questions

  1. #1 Space travel, and gravity and other questions 
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    Well im just a normal person. But I am insanely curious. So these are questions I have always had, just wondering if some one here could answer them. Okay well first is this. How is it that light can slow down in space. Light seems to run out. Like if i have a candle and walk away. Eventually i can't see that light anymore. Do you really think stars are capable of pushing light that far in the universe. And if they were don't you think that would have a insane massive amount of power. That we wouldn't see so many stars in the sky that most would consume each other. Or do you think that something else pushes against light and causes it to slow down. If a star is so capable of such powerful light. Then how come we can't see the planets in our galaxy. But yet we can still see the stars? Wouldn't the sky be filled with stars farther apart? or clusters of them? Also we say we can never travel space well, because of the distance. But How do we even know how fast we can go in 0 gravity? Or if we are in the gravitational pull of another planet. Not one that is pushing us or holding us back. Maybe we are capable of insane speeds outside our galaxy. Also what if we could create artificial gravity would that be our key to space travel. It seems so many ponder how to go the speed of light. But even if we were capable of that. Wouldn't that kind of force effect our earth and galaxy, maybe even destroy it? I just thought which i know maybe i'm wrong. Im not a scientist, just had some thoughts i wanted to seek answers for. But maybe the stars are not as far away as we think. Maybe something holds the light back. Maybe reality it's self has some kind of physical attribute. Also one other thing i'm so curious about. Space can not be explained by all our modern thought. Space is incapable of ending. If it ends there would have to be something else there after it. So does space really have no end? Just goes on forever, that also is impossible. Well thats just what i was thinking about. Please leave a reply and tell me what you think.


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  3. #2  
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    There are a lot of erroneous assumptions in your post. Ask just one question to start and I will make an attempt to answer, or at least provide a link to the proper subject matter.


    I was some of the mud that got to sit up and look around.
    Lucky me. Lucky mud.
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    Cat's Cradle.
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  4. #3 Re: Space travel, and gravity and other questions 
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    Quote Originally Posted by curiousman9999
    Well im just a normal person. But I am insanely curious. So these are questions I have always had, just wondering if some one here could answer them. Okay well first is this. How is it that light can slow down in space. Light seems to run out. Like if i have a candle and walk away. Eventually i can't see that light anymore. Do you really think stars are capable of pushing light that far in the universe. And if they were don't you think that would have a insane massive amount of power. That we wouldn't see so many stars in the sky that most would consume each other. Or do you think that something else pushes against light and causes it to slow down. If a star is so capable of such powerful light. Then how come we can't see the planets in our galaxy. But yet we can still see the stars? Wouldn't the sky be filled with stars farther apart? or clusters of them? Also we say we can never travel space well, because of the distance. But How do we even know how fast we can go in 0 gravity? Or if we are in the gravitational pull of another planet. Not one that is pushing us or holding us back. Maybe we are capable of insane speeds outside our galaxy. Also what if we could create artificial gravity would that be our key to space travel. It seems so many ponder how to go the speed of light. But even if we were capable of that. Wouldn't that kind of force effect our earth and galaxy, maybe even destroy it? I just thought which i know maybe i'm wrong. Im not a scientist, just had some thoughts i wanted to seek answers for. But maybe the stars are not as far away as we think. Maybe something holds the light back. Maybe reality it's self has some kind of physical attribute. Also one other thing i'm so curious about. Space can not be explained by all our modern thought. Space is incapable of ending. If it ends there would have to be something else there after it. So does space really have no end? Just goes on forever, that also is impossible. Well thats just what i was thinking about. Please leave a reply and tell me what you think.
    Light does not slow down in space. It travels at c.

    The intensity if light, in the far field, drops off like the square of the distance. When the intensity is very low your eye does not detect the light.

    Space has no edge. We don't know if it is finite or infinite.

    You have a lot of misconceptions. I suggest that you start by reading A Brief History of Time by Stephen Hawking.
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  5. #4 Re: Space travel, and gravity and other questions 
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    Quote Originally Posted by DrRocket

    Space has no edge. We don't know if it is finite or infinite.

    You have a lot of misconceptions. I suggest that you start by reading A Brief History of Time by Stephen Hawking.
    I haven't read A Brief History of Time but I have read that Hawking wrote (and presumably believed at the time) that space was finite but unbounded.
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  6. #5 Re: Space travel, and gravity and other questions 
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    Quote Originally Posted by Halliday
    Quote Originally Posted by DrRocket

    Space has no edge. We don't know if it is finite or infinite.

    You have a lot of misconceptions. I suggest that you start by reading A Brief History of Time by Stephen Hawking.
    I haven't read A Brief History of Time but I have read that Hawking wrote (and presumably believed at the time) that space was finite but unbounded.
    In general relativity space is a manifold without bound. Whether it is finite or infinite is an open question.
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  7. #6 Re: Space travel, and gravity and other questions 
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    Quote Originally Posted by curiousman9999
    How is it that light can slow down in space. Light seems to run out. Like if i have a candle and walk away. Eventually i can't see that light anymore.
    You seem to be confusing the slowing of light with the apparent brightness of its source. As others have pointed out light does not slow down in space. As to the other point, naturally if light has further to travel it is trying to illuminate a larger surface area with the same number of photons. If must, therefore, appear fainter the further away you are form the source.

    Quote Originally Posted by curiousman9999
    We Do you really think stars are capable of pushing light that far in the universe. And if they were don't you think that would have a insane massive amount of power.
    Of course they are. Go out tonight if the sky is clear and there is your evidence.

    And, you are quite correct. It does take a massive amount of power. Think of the Earth, which intercepts a tiny fraction of the suns output, yet this is sufficient to power the waves and winds and biological cycles of the entire planet. A massive amount of power and this is only from an average star. There are 200 billion (give or take) stars in this galaxy alone. Massive indeed!

    Quote Originally Posted by curiousman9999
    That we wouldn't see so many stars in the sky that most would consume each other. .
    Why would they consume each other? They are very far apart. They are on independent orbits.


    Quote Originally Posted by curiousman9999
    If a star is so capable of such powerful light. Then how come we can't see the planets in our galaxy. But yet we can still see the stars?
    You have answered your own question. Planets are tiny and reflect light, they do not generate it. Stars are massive and generate a great deal of light. With modern telescopes we are now capable of seeing planets around other stars. So far this has been achieved in only one or two cases, but the technology continues to advance.

    Quote Originally Posted by curiousman9999
    Also we say we can never travel space well, because of the distance. But How do we even know how fast we can go in 0 gravity? Or if we are in the gravitational pull of another planet. Not one that is pushing us or holding us back. Maybe we are capable of insane speeds outside our galaxy.
    The principles of physics, which have been validated by countless experiments, require that nothing can exceed the speed of light. Perhaps this belief is in error. Perhaps there are fairies at the bottom of your garden. Perhaps I will change into a giant warthog and consume Buckingham Palace.

    Quote Originally Posted by curiousman9999
    But maybe the stars are not as far away as we think. .
    And maybe I am already on my way to Buckingham Palace. (The Royal Gallery should be especially tasty.) Curiousman, there is no reason to believe the stars are not as far away as we think. We didn't just decide it would be a good idea that they should be far away. We arrived at the conclusion they were far away based on centuries of observation and theorising by hundreds of brilliant minds.

    Quote Originally Posted by curiousman9999
    Space can not be explained by all our modern thought. Space is incapable of ending. If it ends there would have to be something else there after it. So does space really have no end? Just goes on forever, that also is impossible.
    Look at my signature line. There is your answer.
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  8. #7 thank you :) 
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    Thanks for all your replies. I really don't know what i'm talking about lol. Just I think a lot. These are things I always wondered about. So I thought hey ask some people who know LOL. But space is so so amazing. A beautiful mystery fun to think about
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  9. #8  
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    On space being finite or infinite.

    It is both, depending on how you look at it.

    1. It is finite if you work from its origin. The universe began as the Big Bang some 13.7 billion years ago. It has been expanding ever since. It is possible in theory to determine how fast it is expanding, and work back from that to calculate its current volume. Since a given volume is finite, this means the universe is finite.

    2. It is infinite if you work on a beam of light travelling around it. In order to help understanding, I am going to propose an incorrect model. Please do not abuse me for giving a model that is not quite right. It is just a tool to understanding.

    Imagine the universe as an expanding balloon. A very big expanding balloon!
    A beam of light inside that balloon will travel in a circle, following the direction of space. If the 'balloon' is small enough, and expanding slowly enough, that light will eventually travel right round the universe, and come back to where it started.

    Now, the rate of expansion, and the size of the universe is such that, if you fire a laser beam into space, it will never travel to the other side of the universe. Space expands too fast. Since light is the fastest thing that travels, this means we can never detect or measure any part of the universe beyond a certain distance.

    Since it is too far away to ever measure, and continues to expand, that is considered to be the equivalent of infinite in size.
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  10. #9  
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    Quote Originally Posted by skeptic
    On space being finite or infinite.

    It is both, depending on how you look at it.

    1. It is finite if you work from its origin. The universe began as the Big Bang some 13.7 billion years ago. It has been expanding ever since. It is possible in theory to determine how fast it is expanding, and work back from that to calculate its current volume. Since a given volume is finite, this means the universe is finite.

    2. It is infinite if you work on a beam of light travelling around it. In order to help understanding, I am going to propose an incorrect model. Please do not abuse me for giving a model that is not quite right. It is just a tool to understanding.

    Imagine the universe as an expanding balloon. A very big expanding balloon!
    A beam of light inside that balloon will travel in a circle, following the direction of space. If the 'balloon' is small enough, and expanding slowly enough, that light will eventually travel right round the universe, and come back to where it started.

    Now, the rate of expansion, and the size of the universe is such that, if you fire a laser beam into space, it will never travel to the other side of the universe. Space expands too fast. Since light is the fastest thing that travels, this means we can never detect or measure any part of the universe beyond a certain distance.

    Since it is too far away to ever measure, and continues to expand, that is considered to be the equivalent of infinite in size.
    wrong
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  11. #10  
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    Yes, indeed, the universe is a really huge place. 300 sextillion stars is the latest estimate. Whoops, another star just formed. And if the universe expanded into some place already present (by definition?), then the whole shebang could be infinite.

    Although the true meaning of 'infinite' is: something that is never achieved, I'd be hard pressed to say that all of Totality could have an end or a beginning, either in distance or time.
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  12. #11  
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    Quote Originally Posted by questor
    Although the true meaning of 'infinite' is: something that is never achieved, I'd be hard pressed to say that all of Totality could have an end or a beginning, either in distance or time.
    Wrong.

    In this context infinite means "not compact". It is a term from topology.
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  13. #12  
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    Rocket

    You are calling us wrong simply because you do not agree with definitions we are using. Sometimes it helps to expand your vision a little.
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  14. #13  
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    [quote="skeptic"]Rocket

    You are calling us wrong simply because you do not agree with definitions we are using. Sometimes it helps to expand your vision a little.[/quote

    Sometimes it helps tp put you brain in gear before you let out the clutch on your mouth.

    The definition I gave you is the one used in cosmology. The question at hand is one of cosmology.
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  15. #14  
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    Rocket

    I pointed out that the universe might be regarded as finite or infinite depending on how you look at it.
    http://en.wikipedia.org/wiki/Infinity#Cosmology

    I quote :

    "If, on the other hand, the universe were not curved like a sphere but had a flat topology, it could be both unbounded and infinite. The curvature of the universe can be measured through multipole moments in the spectrum of the cosmic background radiation. As to date, analysis of the radiation patterns recorded by the WMAP spacecraft hints that the universe has a flat topology. This would be consistent with an infinite physical universe. The Planck spacecraft launched in 2009 is expected to record the cosmic background radiation with 10 times higher precision, and will give more insight into the question whether the universe is infinite or not."


    Current knowledge indicates the universe is probably flat. This means it is impossible even for a beam of light to travel around it, which is consistent with the universe being infinite. This tends to be the majority view by cosmologists.
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  16. #15  
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    Quote Originally Posted by skeptic
    Rocket

    I pointed out that the universe might be regarded as finite or infinite depending on how you look at it.
    Wrong. Moreover the passage that you quote below shows this statement to be wrong.

    [quote="skeptic"]http://en.wikipedia.org/wiki/Infinity#Cosmology

    I quote :

    "If, on the other hand, the universe were not curved like a sphere but had a flat topology, it could be both unbounded and infinite. The curvature of the universe can be measured through multipole moments in the spectrum of the cosmic background radiation. As to date, analysis of the radiation patterns recorded by the WMAP spacecraft hints that the universe has a flat topology. This would be consistent with an infinite physical universe. The Planck spacecraft launched in 2009 is expected to record the cosmic background radiation with 10 times higher precision, and will give more insight into the question whether the universe is infinite or not."
    [quote]

    This is a bit misleading. Curvature does not determine topology without additional assumptions. If one makes the "cosmological assumption that the universe is homogeneous and isotropic then flat curvature implies that space is Euclidean, a negative curvature thatn it is hyperbolic, and a positive curvature that it is spherical.

    Data to date indicates that the curvature is very small, but could be positive, negative or zero.


    Quote Originally Posted by skeptic
    Current knowledge indicates the universe is probably flat. This means it is impossible even for a beam of light to travel around it, which is consistent with the universe being infinite. This tends to be the majority view by cosmologists.
    Wrong

    Nobody knows if space is finite or infinite. See above. There is no "vote", and there would be no meaning if there were one.

    Wiki is not always accurate.
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  17. #16  
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    Rocket

    I accept that there is doubt over this question. However, it is important to realise that there are two ways of looking at this, and the answer will depend on your definition of infinite.

    Another way of looking at the question

    http://www.esa.int/esaSC/SEMR53T1VED_index_0_iv.html

    I quote :

    "ESA: Is the Universe finite or infinite?

    Joseph Silk: We don't know. The expanding Universe theory says that the Universe could expand forever [that corresponds to a 'flat' Universe]. And that is probably the model of the Universe that we feel closest to now. But it could also be finite, because it could be that the Universe has a very large volume now, but finite, and that that volume will increase, so only in the infinite future will it actually be infinite."


    ESA is the European Space Agency and Joseph Silk is Professor of Astrophysics at the University of Oxford, UK. Rather credible sources. A 'flat' universe is regarded as infinite, as shown in the NASA quote below.

    What does NASA say?
    http://wmap.gsfc.nasa.gov/universe/uni_shape.html

    I quote :

    "We now know that the universe is flat with only a 2% margin of error."

    NASA also says
    http://wmap.gsfc.nasa.gov/universe/bb_concepts.html

    and I quote : The universe ...

    " can be "positively" curved like the surface of a ball and finite in extent; it can be "negatively" curved like a saddle and infinite in extent; or it can be "flat" and infinite in extent"

    Since being flat makes it infinite in extent, and WMAP measurements show it almost certainly to be very close to flat, then we can regard the universe as infinite. At the same time, looked at another way, we can regard it as finite. Two views, both likely to be correct.

    Here is a reference that explains it in the same way I did in my earlier post.
    http://www.universetoday.com/38269/infinite-universe/

    "A photon that follows a straight path on a finite universe may end up in the same spot as when it first started out, while a photon that would head out in the same manner on an infinite one will never find its way back (as long as it doesnít turn back, of course!).

    Is there a way to determine whether the Universe is infinite or finite? Apparently, its geometry (open, closed, or flat) is largely dependent on the density of matter in it.

    That is, if the density of matter is larger than a certain value, known as the critical density, the geometry should be closed. If it is less than the said value, the geometry should be open. And if it is equal to the critical density, then it should be flat.

    Measurements made on the cosmic microwave background radiation by WMAP point to a curvature that can be well considered flat. In other words, we most likely have an infinite universe."
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  18. #17  
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    Quote Originally Posted by skeptic
    Rocket

    I accept that there is doubt over this question. However, it is important to realise that there are two ways of looking at this, and the answer will depend on your definition of infinite.

    Wrong.

    Read your own damn link to see why.

    http://www.esa.int/esaSC/SEMR53T1VED_index_0_iv.html



    Quote Originally Posted by skeptic
    Another way of looking at the question

    I quote :

    "ESA: Is the Universe finite or infinite?

    Joseph Silk: We don't know. The expanding Universe theory says that the Universe could expand forever [that corresponds to a 'flat' Universe]. And that is probably the model of the Universe that we feel closest to now. But it could also be finite, because it could be that the Universe has a very large volume now, but finite, and that that volume will increase, so only in the infinite future will it actually be infinite."
    This is NOY another way to look at it. It is just a simplified explanation for what an expanding finite space is.


    Quote Originally Posted by skeptic
    What does NASA say?
    http://wmap.gsfc.nasa.gov/universe/uni_shape.html

    I quote :

    "We now know that the universe is flat with only a 2% margin of error."
    Yep. That is consistent with what I told you, and does NOT tell us whether the universe is finite or infinite at all.

    Quote Originally Posted by skeptic
    NASA also says
    http://wmap.gsfc.nasa.gov/universe/bb_concepts.html

    and I quote : The universe ...

    " can be "positively" curved like the surface of a ball and finite in extent; it can be "negatively" curved like a saddle and infinite in extent; or it can be "flat" and infinite in extent"
    Which is PRECISELY wha I said above, with the assumption of homogeneity and isotropy. It does not btell uw whetherv the universe is finite or infinite.


    Quote Originally Posted by skeptic
    Since being flat makes it infinite in extent, and WMAP measurements show it almost certainly to be very close to flat, then we can regard the universe as infinite. At the same time, looked at another way, we can regard it as finite. Two views, both likely to be correct.
    Nope. Completely wrong.

    Quote Originally Posted by skeptic
    Here is a reference that explains it in the same way I did in my earlier post.
    http://www.universetoday.com/38269/infinite-universe/
    Which simply lists the three possibilities for the topology of a homogeneous and isotropic universe.

    You would be better off listening and learning something than offering citations that you don't understand and that contradict your assertions.
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  19. #18  
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    Rocket

    What is wrong with you?
    The reference says, simply and unambiguously, that a flat universe is infinite.
    It also says clearly that our universe is probably flat.
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  20. #19  
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    Quote Originally Posted by skeptic
    Rocket

    What is wrong with you?
    The reference says, simply and unambiguously, that a flat universe is infinite.
    It also says clearly that our universe is probably flat.
    What is wrong is that I actually understand what was said, and apparently you don't.

    The univerese is nearly flat and that is not nearly enough to determine if it is infinite or finite.

    Stop arguing and learn something.
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  21. #20  
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    What is ambiguous about the following statement, from the Universe Today reference?

    "Measurements made on the cosmic microwave background radiation by WMAP point to a curvature that can be well considered flat. In other words, we most likely have an infinite universe"
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  22. #21  
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    Quote Originally Posted by skeptic
    What is ambiguous about the following statement, from the Universe Today reference?

    "Measurements made on the cosmic microwave background radiation by WMAP point to a curvature that can be well considered flat. In other words, we most likely have an infinite universe"
    That article was written by a reporter who understands the issue about as well as you do. There are all sorts of inaccuracies over-simplifications and mistakes in it.

    Don't believe everything that you see on the internet. If you can find it there is a pretty good article br Geroch and Horowitz, "Global structure of spacetimes" in General relativity, An Einstein Centenary Survey edited by Hawking and Israel.

    You can find a somewhat more limited discussion in Gravitation and cosmology : principles and applications of the general theory of relativity by Steven Weinberg.

    Quit arguing, listen and learn. Or at least go read some serious science books, not popularizations and internet junk.
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  23. #22  
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    Cosmology is the study of the universe. General relativity of course deals with the effect of gravity curving the spacetime of the universe. Depending on a certain value for the density of the universe, called omega, you will get one of three different effects. If it is greater than one, then the universe will eventually curve back on itself. So the topology or cosmological shape of the universe would be like a sphere and the universe would eventually close back into a Big Crunch. If it is less than one, then the universe is like a saddle curving away and the universe would expand forever. If it is exactly one then the universe is flat and the universe will continue to expand, but at an ever slower rate.
    http://www.absoluteastronomy.com/top...f_the_Universe
    Now when most people say universe we mean everything that exists. However, to a cosmologist there are two universes. The observable universe contains all objects whose light has reached us since the Big Bang and the whole universe, which is the observable universe plus anything else. The observable universe can be amazingly flat, locally, and the universe may still eventually curve like a saddle. So WMAP only applies to the observable universe. The observable universe is finite, but expanding in all directions, so it is unbounded. The whole universe could have been infinite right from the Big Bang, i.e., an infinitely large dense state inflating in all directions. We just donít know conclusively.
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  24. #23  
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    I think I give up. Dr Rocket claims that NASA and ESA are "popularizations and internet junk."

    Some people need to have the truth wrapped in a brick and whacked over their head, and they still will not see it.
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  25. #24  
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    Quote Originally Posted by skeptic
    I think I give up. Dr Rocket claims that NASA and ESA are "popularizations and internet junk."
    That is ridiculous. You are NOT reading either NASA or ESA scientific publications. You are reading popular articles written by reporters interviewing employees of those organizations, or public relations pieces. Moreover, the interviews do not say what you seem to think that they say.

    What you have been reading is indeed "popularizations and internet junk."

    I gave you some references to real scientific articles intended for an audience of scientists. Go read them.

    Quote Originally Posted by skeptic
    Some people need to have the truth wrapped in a brick and whacked over their head, and they still will not see it.
    You have just described yourself.

    I have tried to provide you a bit of insight, which you refuse. Go do the work to get your own PhD and then maybe we can communicate.
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  26. #25  
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    Rocket

    Almost everything written under the auspices of NASA or ESA can be described as :
    "popular articles written by reporters interviewing employees of those organizations, or public relations pieces"

    You cannot reject material from those august organisations so lightly and remain credible.

    You suggested that the universe is finite, and I agreed.
    You pointed out that finite/infinite is uncertain and I agreed with that also.

    However, I went ahead and pointed out that the universe can also be regarded, from one point of view, as infinite, and showed clear references from reputable authorities to demonstrate this point, and you respond with insults.

    Sorry, but on that point, you are either wrong or have misinterpreted what I have said. I suggest you re-think.
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  27. #26  
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    This is where I think the problem started...

    Quote Originally Posted by skeptic
    On space being finite or infinite.

    It is both, depending on how you look at it.

    1. It is finite if you work from its origin. The universe began as the Big Bang some 13.7 billion years ago. It has been expanding ever since. It is possible in theory to determine how fast it is expanding, and work back from that to calculate its current volume. Since a given volume is finite, this means the universe is finite.
    That refers only to the observable universe. We have no reason to think the observable universe is the whole universe, and every reason to think there is more universe than just the part we have observed so far. Of course, the observable universe is finite, as our observations are limited by the time that light has had to travel, but that does not mean that the whole universe is finite.

    Quote Originally Posted by skeptic
    2. It is infinite if you work on a beam of light travelling around it. In order to help understanding, I am going to propose an incorrect model. Please do not abuse me for giving a model that is not quite right. It is just a tool to understanding.

    Imagine the universe as an expanding balloon. A very big expanding balloon!
    A beam of light inside that balloon will travel in a circle, following the direction of space. If the 'balloon' is small enough, and expanding slowly enough, that light will eventually travel right round the universe, and come back to where it started.

    Now, the rate of expansion, and the size of the universe is such that, if you fire a laser beam into space, it will never travel to the other side of the universe. Space expands too fast. Since light is the fastest thing that travels, this means we can never detect or measure any part of the universe beyond a certain distance.

    Since it is too far away to ever measure, and continues to expand, that is considered to be the equivalent of infinite in size.
    No, that is a cosmological event horizon that limits the future size of our observable universe, and exists due to the acceleration of the expansion of the universe, but does not address the question as to whether the universe is finite or infinite.

    The question as to whether the universe is finite, or infinite, is a question of topology, something that none of the above addresses adequately.

    This business of light circumnavigating or reaching the other side of the universe is a red herring. There are finite topologies where light cannot circumnavigate the universe and end up back where it started. There are flat, finite topologies where light can travel through the universe forever and never come back to the same place!

    Also, saying that the rate of expansion means that light cannot circumnavigate the universe, or that there will be parts of the universe we will never see, is no evidence for either a finite, or an infinite universe.

    Quote Originally Posted by skeptic
    I pointed out that the universe might be regarded as finite or infinite depending on how you look at it.
    It is finite in time. It might be finite or infinite in space.

    Quote Originally Posted by skeptic
    http://en.wikipedia.org/wiki/Infinity#Cosmology

    I quote :

    "If, on the other hand, the universe were not curved like a sphere but had a flat topology, it could be both unbounded and infinite. The curvature of the universe can be measured through multipole moments in the spectrum of the cosmic background radiation. As to date, analysis of the radiation patterns recorded by the WMAP spacecraft hints that the universe has a flat topology. This would be consistent with an infinite physical universe. The Planck spacecraft launched in 2009 is expected to record the cosmic background radiation with 10 times higher precision, and will give more insight into the question whether the universe is infinite or not."


    Current knowledge indicates the universe is probably flat. This means it is impossible even for a beam of light to travel around it, which is consistent with the universe being infinite. This tends to be the majority view by cosmologists.
    Ahh, now here we are, some mention of the topology, rather than simply the finite volume of the observable universe, or the expansion rate precluding us from seeing the other side of the universe!

    Note that the Planck spacecraft will give us more insight into the question whether the universe is infinite or not.

    It is an open question in cosmology, whatever side of the fence cosmologists sit on. We may indeed never be able to know if the universe is finite or infinite.

    But if one thing is sure, it is that it is not both!
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  28. #27  
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    Quote Originally Posted by SpeedFreek
    This is where I think the problem started...

    Quote Originally Posted by skeptic
    On space being finite or infinite.

    It is both, depending on how you look at it.

    1. It is finite if you work from its origin. The universe began as the Big Bang some 13.7 billion years ago. It has been expanding ever since. It is possible in theory to determine how fast it is expanding, and work back from that to calculate its current volume. Since a given volume is finite, this means the universe is finite.
    That refers only to the observable universe. We have no reason to think the observable universe is the whole universe, and every reason to think there is more universe than just the part we have observed so far. Of course, the observable universe is finite, as our observations are limited by the time that light has had to travel, but that does not mean that the whole universe is finite.
    I don't think so.

    1. The observable universe is not only finite, but also has a boundary. There is no controversy about this fact. This has nothing whatever to do with curvature or even expansion, only with the finite speed of light and finite age of the universe. The universe in cosmological terms is a manifold without boundary.

    2. There is no origin in the sense used above. This demonstrates a fundamental lack of understanding of the big bang and of spacetime.

    3. I have no idea what "a given volume" is, but there is absolutely no reason why the volume of the univeerse, or an unbounded open submanifold, cannot be infinite.

    The fundamental problem is that skeptic lacks the background in mathematics to understand cosmological models.


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  29. #28  
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    Of course. I agree, but my reply was addressing what I think he actually meant - i.e. if we know the age of the universe (I took origin to mean in time) and we know how much the observable universe has expanded, we can work out its volume. This is true, but it only applies the observable universe, and says nothing about the "shape" or size of the universe as a whole.
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  30. #29  
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    The only thing I lack is the patience to put up with those who either cannot understand what I say, or cannot accept what the real experts at NASA and ESA say.
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  31. #30  
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    Quote Originally Posted by skeptic
    The only thing I lack is the patience to put up with those who either cannot understand what I say, or cannot accept what the real experts at NASA and ESA say.
    You don't understand what you say. You don't understand that which you quote either, since it contradicts your own words.

    It is not a matter of patience, but rather of understanding and the ability to reason correctly from what is understood.
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  32. #31  
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    Quote Originally Posted by SpeedFreek
    Of course. I agree, but my reply was addressing what I think he actually meant - i.e. if we know the age of the universe (I took origin to mean in time) and we know how much the observable universe has expanded, we can work out its volume. This is true, but it only applies the observable universe, and says nothing about the "shape" or size of the universe as a whole.
    I used the modifying phrase "in theory". Of course we need more data than we currently have, and we may never have that data, but the theory is still OK.
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  33. #32  
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    Quote Originally Posted by skeptic
    Quote Originally Posted by SpeedFreek
    Of course. I agree, but my reply was addressing what I think he actually meant - i.e. if we know the age of the universe (I took origin to mean in time) and we know how much the observable universe has expanded, we can work out its volume. This is true, but it only applies the observable universe, and says nothing about the "shape" or size of the universe as a whole.
    I used the modifying phrase "in theory". Of course we need more data than we currently have, and we may never have that data, but the theory is still OK.
    You realize, of course, that Speedfreak's agreement was in response to my post, which immediately preceded his.
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