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Lots of questions

  1. Sep 7, 2011 #1
    I have lots of questions, they occured to me last year during the physic/chemistry class and I asked the teacher and she couldnt answer. First: Is the universe tridemensional?? Second: If yes, wich is what I believe so, Why do we see stars and planets and galaxies always in a straight line??(with this question I pretend to know if there is any planet or star or galaxie below or over the earth, instead of beeing everything in a straight line). Third: The energy wich was "released" when big bang occured it's not reciclable, but when a star dies, for example, doesnt it recicle the energy present in the universe or does it just exepel heavy metals to the universe not recicling matter?? Fourth: I know this is more a chemistry question, but what is the compostion of fire (i dont konw if someone has already discovered it)? Fifth: I dont uderstand the Time question, I mean, for example why do people say that if you're travelling at light speed the time passes by faster for other people than to you? (concrete example, I enter in a train travelling at light speed, I look at the clock and it's 10:00am, when i get out, i look at the clock and it shows 10:20am, but outside the train many years have passed, is this really true??), so, simply how can we define time??

    Sorry for my english, its probably a bit confusing.
    When you leave an answer to a question, please identify wich, Thank you.
  2. jcsd
  3. Sep 7, 2011 #2
    Hi Nogueira, I can't quite understand all of your questions, but I'll answer the ones I can and tell you the ones I'm not quite sure about.

    1. Assuming you mean the number of spatial dimensions, General Relativity calls for 3 spatial dimensions plus a fourth dimension of time, and this theory has been rigorously tested and has prevailed. While some other theories call for more dimensions (11 is an often quoted number), there is little experimental basis for this.

    2) I'm not quite sure what you mean by this, if you mind rephrasing I might be able to help.

    3) One of the fundamental pillars of physics is that energy cannot be created or destroyed, when a star goes supernova (for example), all of the energy (and by extension matter) in it, is either pushed out into a planetary nebula or retained in the shell (white dwarf) of the star, but the total matter is the same before and after.

    4) Fire is not a substance in itself, it is (and someone who knows more than me feel free to correct me) a chemical reaction, while I don't remember the exact chemical equation, fire is not an element in itself but heat and light given off by a reaction.

    5) It's one of the easier things in General Relativity to understand but it's sort of hard to explain in text so here's a video that explains it:

    (The one thing the video doesn't directly explain is that one of the postulates of General Relativity is that the speed of light is constant for all observers)

    I hope this helped!
    Last edited by a moderator: Sep 25, 2014
  4. Sep 7, 2011 #3


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    Time and space are squishy [and interchangeable] under general relativity.
  5. Sep 8, 2011 #4
    Hi Vorde, thanks, for the enlightment.
    "2) I'm not quite sure what you mean by this, if you mind rephrasing I might be able to help."
    I'll try to refrase, if you see, for example, a picture of the solar sistem, you will notice that all the planets and the sun, are vertically aligned, i mean they are all in "the same plan" all aligned nothing below, nothing over. Uh, my problem is really hard to put in words. Does anything exists below or over the earth?? Or do we live in a 2dimensional (from arts point of view) universe, I mean we have lenght, depth, but no height (void over and below us).
  6. Sep 8, 2011 #5
    The Universe looks the same in all directions, the planets orbit ina plane but this is just orbital dynamcis - orbital planes are at different angles. The Universe looking the same in all directions is a key principle in modern cosmology, called homogeneity or isotropy.
  7. Sep 8, 2011 #6
    The planets might be all on the same plane (not exactly though, and there are exceptions), but the universe isn't. Look up, look down, look left look right you'll see stars in every direction.
  8. Sep 8, 2011 #7
    No, if that is what you mean it is just incorrect....things might superficially appear to be arranged in approximately a sphere, but they vary in distance from our moon which is close out to our sun and further out to the Andromeda Galaxy (our nearest galactic neighor) and waaaaay beyond that to about 46 billion light years...the outer reaches of the observable universe...and the oldest light we can detect.
    The sun and moon remain about the same distance from earth, but the further out one looks the faster one finds movement of entities away from each other and from us.
  9. Sep 8, 2011 #8
    Basically there is stuff in every direction. The fact that all planets all orbit in (practically) the same orientation is a result of orbital mechanics.
  10. Sep 8, 2011 #9


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    We do in fact live in a 3D (or possibly 4D) universe! All of the planets and their moons occupy orbits that vary slightly in inclination.(How far "up" or "down" from the average orbital plane an orbit varies) Pluto, which was actually demoted from planet status recently, has its orbit at an inclination of 17 degrees! (Which is waaay bigger than any of the current planets inclinations) In addition, the solar system's own ecliptic plane is at 60 degrees of inclination in relation to the rest of the galaxy!
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