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This didn't mention the expansion of space at all. The universe may be infinite in size but we'll never see the light of stars that exist so far from us that th

by VeilEm 11y ago

This didn't mention the expansion of space at all. The universe may be infinite in size but we'll never see the light of stars that exist so far from us that they are beyond the distance at which space expands faster than light can travel. That's why we have a dark sky and it will just get darker as more things we see now eventually expand beyond that barrier. One suggested end to the universe is the Big Rip in which all matter eventually separates in this way such that the distance between all matter is infinite: https://en.wikipedia.org/wiki/Big_Rip https://en.wikipedia.org/wiki/Big_Rip

ranko 11y ago
The expansion of the universe also leads to red shift of the light from (nearly) all the stars that we'd otherwise expect to see. This means that the frequency of their light is moved away from the range that our eyes can see.
platz 11y ago
My understanding of the expansion of space is that the expansion doesn't occur locally, but is only noticeable over large distances. is that incorrect?
- paulddraper 11y ago
  It occurs everywhere, proportionally. The effect isn't great enough to notice unless you are looking at light-years. Also, gravity and electromagnetism increase at close proximity, so on less-than-cosmic scales, they overcome the minute amount of spatial expansion.
  - platz 11y ago
    therefore the statement " all matter eventually separates in this way" , strictly speaking, seems false since gravity and electromagnetism overcome expansion at local levels.
    - paulddraper 11y ago
      Yeah, both are right in context. It's just like saying "gravity doesn't make objects fall at the same speed". It actually does make them fall at the same speed...but if you include other relevant forces, the overall effect is different. FYI, gravity might eventually overcome spatial expansion on a cosmic scale. But we don't know. https://en.wikipedia.org/wiki/Big_Crunch https://en.wikipedia.org/wiki/Big_Crunch
      - typon 11y ago
        I thought the Big Crunch was disproven because we found that the expansion of the Universe is accelerating. Dark Energy wins over Dark Matter...forever.
        paulddraper 11y ago
        More likely than not, the Big Crunch will not happen. From Wikipedia: "Recent experimental evidence (namely the observation of distant supernovae as standard candles, and the well-resolved mapping of the cosmic microwave background) has led to speculation that the expansion of the universe is not being slowed down by gravity but rather accelerating. However, since the nature of the dark energy that is postulated to drive the acceleration is unknown, it is still possible (though not observationally supported as of today) that it might eventually reverse its developmental path and cause a collapse."
        joehilton 11y ago
        It was my understanding that this is true from our perspective in time right now, but the Big Crunch could still be plausible if the universe turns out to be young enough (which it seems like it is) that not all the fusion fuel has been exhausted. Once it is, we'll have big clouds of nuclear waste interspersed between black holes, and perhaps in this environment the Big Crunch could still occur. I think another question for the Big Crunch is what type of "fuel" is needed to create an exothermic fusion reaction comparable to the Big Bang? For example, the sun compresses hydrogen to produce helium and release massive energy. Black holes are undoubtedly compressing helium enough to make Beryllium, but this doesn't seem to release any energy that can escape the gravity that created the pressure required in the first place. So for the Big Crunch - Big Bang cycle to hold up, what type of matter (and how much of it) has be be compressed (and is gravity the only force that's compressing it) to the point where some type of "fusion" reaction produces enough energy to escape the compression forces?
paulddraper 11y ago
Yep. Currently, some galaxies are traveling away from us faster than light. http://curious.astro.cornell.edu/about-us/104-the-universe/cosmology-and-the-big-bang/expansion-of-the-universe/616-is-the-universe-expanding-faster-than-the-speed-of-light-intermediate http://curious.astro.cornell.edu/about-us/104-the-universe/c...
- joering2 11y ago
  That blew my mind! So now it turns out Einstein was wrong?? We can't get particle to seriously travel faster than light and there is entire galaxy going faster??
  - dsmithatx 11y ago
    I don't think it means Einstein was wrong or that one galaxy is moving "faster than the speed of light". It means in respect to each other two galaxies are moving faster than the speed of light. In other words each of two galaxies is going faster than half the speed of light, one of them being us (in relation to the other observed Galaxy).
    - tamana 11y ago
      That's extremeley not true, and the whole point of Relatively is to explain why.
  - deleted 11y ago
    [deleted]
  - joehilton 11y ago
    I've also had a long-time question around this point. I've asked various university physics professors, and they all stutter and disagree (which means either we really don't know or I'm going to all the wrong universities). The underlying question is: When we say in general relativity that particles can't travel faster than light, what is that speed measured relative to? If it's photons emitting from flashlights pointed in opposite directions relative to each other, then are they compressing space as they travel so as not to exceed the speed of light? Or even massive particles accelerated to over half the speed of light at different times around an ellipse so there is a moment when their opposite directions make one traveling at greater than the speed of light relative to the other? (Or even particle accelerators on two different planets already expanding away from each other - does this just mean that space is really twisting and turning all the time to make sure no particle ever exceeds the speed of light relative to any other particle?) It has been my understanding - and appreciation at Einstein's unbelievable insight and brilliance - that relativity is truly relative because there really isn't any such thing as an arbitrary particle or space that all other motions are measured from. But if this is true, does that really mean that space is really so constantly twisting and turning that SOL can't be exceeded? I'm sure there are great answers to this, but I've always wanted a definitive one. Anyone have any comments on this?

by VeilEm 11y ago

ranko 11y ago

The expansion of the universe also leads to red shift of the light from (nearly) all the stars that we'd otherwise expect to see. This means that the frequency of their light is moved away from the range that our eyes can see.

platz 11y ago

My understanding of the expansion of space is that the expansion doesn't occur locally, but is only noticeable over large distances. is that incorrect?

paulddraper 11y ago
It occurs everywhere, proportionally. The effect isn't great enough to notice unless you are looking at light-years. Also, gravity and electromagnetism increase at close proximity, so on less-than-cosmic scales, they overcome the minute amount of spatial expansion.
- platz 11y ago
  therefore the statement " all matter eventually separates in this way" , strictly speaking, seems false since gravity and electromagnetism overcome expansion at local levels.
  - paulddraper 11y ago
    Yeah, both are right in context. It's just like saying "gravity doesn't make objects fall at the same speed". It actually does make them fall at the same speed...but if you include other relevant forces, the overall effect is different. FYI, gravity might eventually overcome spatial expansion on a cosmic scale. But we don't know. https://en.wikipedia.org/wiki/Big_Crunch https://en.wikipedia.org/wiki/Big_Crunch
    - typon 11y ago
      I thought the Big Crunch was disproven because we found that the expansion of the Universe is accelerating. Dark Energy wins over Dark Matter...forever.
      - paulddraper 11y ago
        More likely than not, the Big Crunch will not happen. From Wikipedia: "Recent experimental evidence (namely the observation of distant supernovae as standard candles, and the well-resolved mapping of the cosmic microwave background) has led to speculation that the expansion of the universe is not being slowed down by gravity but rather accelerating. However, since the nature of the dark energy that is postulated to drive the acceleration is unknown, it is still possible (though not observationally supported as of today) that it might eventually reverse its developmental path and cause a collapse."
      - joehilton 11y ago
        It was my understanding that this is true from our perspective in time right now, but the Big Crunch could still be plausible if the universe turns out to be young enough (which it seems like it is) that not all the fusion fuel has been exhausted. Once it is, we'll have big clouds of nuclear waste interspersed between black holes, and perhaps in this environment the Big Crunch could still occur. I think another question for the Big Crunch is what type of "fuel" is needed to create an exothermic fusion reaction comparable to the Big Bang? For example, the sun compresses hydrogen to produce helium and release massive energy. Black holes are undoubtedly compressing helium enough to make Beryllium, but this doesn't seem to release any energy that can escape the gravity that created the pressure required in the first place. So for the Big Crunch - Big Bang cycle to hold up, what type of matter (and how much of it) has be be compressed (and is gravity the only force that's compressing it) to the point where some type of "fusion" reaction produces enough energy to escape the compression forces?

paulddraper 11y ago

Yep. Currently, some galaxies are traveling away from us faster than light. http://curious.astro.cornell.edu/about-us/104-the-universe/cosmology-and-the-big-bang/expansion-of-the-universe/616-is-the-universe-expanding-faster-than-the-speed-of-light-intermediate http://curious.astro.cornell.edu/about-us/104-the-universe/c...

joering2 11y ago
That blew my mind! So now it turns out Einstein was wrong?? We can't get particle to seriously travel faster than light and there is entire galaxy going faster??
- dsmithatx 11y ago
  I don't think it means Einstein was wrong or that one galaxy is moving "faster than the speed of light". It means in respect to each other two galaxies are moving faster than the speed of light. In other words each of two galaxies is going faster than half the speed of light, one of them being us (in relation to the other observed Galaxy).
  - tamana 11y ago
    That's extremeley not true, and the whole point of Relatively is to explain why.
- deleted 11y ago
  [deleted]
- joehilton 11y ago
  I've also had a long-time question around this point. I've asked various university physics professors, and they all stutter and disagree (which means either we really don't know or I'm going to all the wrong universities). The underlying question is: When we say in general relativity that particles can't travel faster than light, what is that speed measured relative to? If it's photons emitting from flashlights pointed in opposite directions relative to each other, then are they compressing space as they travel so as not to exceed the speed of light? Or even massive particles accelerated to over half the speed of light at different times around an ellipse so there is a moment when their opposite directions make one traveling at greater than the speed of light relative to the other? (Or even particle accelerators on two different planets already expanding away from each other - does this just mean that space is really twisting and turning all the time to make sure no particle ever exceeds the speed of light relative to any other particle?) It has been my understanding - and appreciation at Einstein's unbelievable insight and brilliance - that relativity is truly relative because there really isn't any such thing as an arbitrary particle or space that all other motions are measured from. But if this is true, does that really mean that space is really so constantly twisting and turning that SOL can't be exceeded? I'm sure there are great answers to this, but I've always wanted a definitive one. Anyone have any comments on this?