Ok so these days, everything I read about the nature of the universe says that it's expansion is accelerating. Because of this, it is said that the universe may end with everything just ripping apart.
My question is: Why do physicists or whoever think that the universe won't slow down again?
Ok, now, I would like to make sure my understanding of the big bang is correct. Obviously this is a very simple understanding of it and I may be totally wrong here but I guess that's why I am asking.
Is it correct for me to interpret the big bang as something like an infinitely small spinning point, that suddenly explodes in mass, spinning out matter/energy in all directions outward from it's center point?
I ask because if that is how the universe has been formed, then wouldn't it only be natural that some matter would be shot out farther and at a much higher rate than other matter?
Like, if the milky way was somewhat near the center, it would have shot out slowly and "quickly" began deceleration. Whereas a galaxy much farther away from us could be likely to still be accelerating, but eventually slowing down, no? Just like if you put some paint in the middle of a paper plate and spun it at an extremely high rate. What is flung out closest to the center decelerates the fastest, and what is flung out the farthest continues to accelerate longer.
Uhhh if the 'explosion' or big bang is the only thing propelling the galaxies outwards, then there is no force causing any of the galaxies to continue accelerating away from the center. Like, whatever force causes the Milky Way to decelerate should cause further galaxies to also decelerate, even if the effect is smaller. I think this is the surprising part of the expansion, not the fact that some things are further/started out faster.
I think the theory of expanding-contracting is more popular than expanding-ripping apart? that the galaxy is expanding and at some point will reach some critical limit and then contract again, like with a rubber band; if you stretch it far enough at some point it's going to snap back to its original position (or just rip I guess)....
On April 07 2009 04:47 bludragen88 wrote: Uhhh if the 'explosion' or big bang is the only thing propelling the galaxies outwards, then there is no force causing any of the galaxies to continue accelerating away from the center. Like, whatever force causes the Milky Way to decelerate should cause further galaxies to also decelerate, even if the effect is smaller. I think this is the surprising part of the expansion, not the fact that some things are further/started out faster.
Yes and what I am saying is that it will cause them to decelerate, it just hasn't begun to yet.
Basically I don't understand why it's such a big deal to astronomers that expansion is still accelerating.
Unless my understanding is wrong and everything is accelerating, not just the points further from the "center"
There is no way to know where the center is, but astronomers seem to think that galaxies are in general spreading out faster.
Currently that means that the matter -> energy conversion is causing matter to move apart faster. The amount of energy being produced is stronger than gravity. I'm not sure what the long term trends are.
Acceleration could be decreasing. In which case there may be an eventual slow down of expansion or even a contraction. Acceleration could be increasing in which case, matter will fly apart faster than ever.
On April 07 2009 04:47 bludragen88 wrote: Uhhh if the 'explosion' or big bang is the only thing propelling the galaxies outwards, then there is no force causing any of the galaxies to continue accelerating away from the center. Like, whatever force causes the Milky Way to decelerate should cause further galaxies to also decelerate, even if the effect is smaller. I think this is the surprising part of the expansion, not the fact that some things are further/started out faster.
Yes and what I am saying is that it will cause them to decelerate, it just hasn't begun to yet.
Basically I don't understand why it's such a big deal to astronomers that expansion is still accelerating.
Unless my understanding is wrong and everything is accelerating, not just the points further from the "center"
I think the main problem here is that... things that are a big deal to astronomers are a big deal because they don't have a lot to be excited about, not necessarily because they're a big deal. They must do the most interpretation of the least data out of any field of science... or anything at all.
I still think the fact that the expansion is still accelerating is surprising and a big deal, because something must be propelling these fringes away from the center in order for the acceleration to increase. Even if something will cause them to decelerate, the fact that they haven't yet, and are still accelerating, is odd, even if that trend reverses itself at some point. This would also imply the whole ripping apart consequence if it continues, which would also be interesting because that implies a non-cyclic fate of our universe (no return to a single point followed by future big bang).
My question is: Why do physicists or whoever think that the universe won't slow down again?
If there is enough matter in the universe then all that matter has enough mass, causing enough gravity, to make it contract again.
Currently the universe is expanding at increasing velocity and it doesn't look like it has anywhere close to enough to start to contract.
Is it correct for me to interpret the big bang as something like an infinitely small spinning point, that suddenly explodes in mass, spinning out matter/energy in all directions outward from it's center point?
No. The universe is expanding and if you calculate back everything it came from one single point. It's not a singularity that exploded or spewed out matter. The universe isn't expanding right now because the outer shell of stars is being thrown away from the center. No, the space between the stars is increasing. Ignore the matter in the universe itself. The universe itself inflated from a single point into what it is now. During all that time a lot happened to the matter inside the universe. But that's a different issue.
On April 07 2009 04:49 Xeris wrote: I think the theory of expanding-contracting is more popular than expanding-ripping apart? that the galaxy is expanding and at some point will reach some critical limit and then contract again, like with a rubber band; if you stretch it far enough at some point it's going to snap back to its original position (or just rip I guess)....
don't know which is correct (if any of them are) O_O!
contraction is not part of an expanding universe you mean total loss of entropy or freeze over which is the consensus of how the universe will end.
Really both gives the same result total loss of entropy leads to even the 4 main powers in the universe loosing their ability to hold anything together.
speeding up leads to a state at which the 4 powers are overpowered and all matter is torn into nothingness
Really they are the same results.
Only reason why there is a theory of speed up is that dark energy is currently release its energy causing an acceleration of the expansion, it has been known for quite some time that with the creation of the universe that there is dark energy to a fineamount that will always be around it's just not until recently that it's realse of energy has been noticed.
You know what escape velocity is, right? It's the velocity an object must be travelling in order to ecape the pull of the gravity of any given mass.
We can measure the rate of expansion of the universe (if you want more details, ask), so the theory is, if the universe is expanding faster than its own escape velocity, then it will never compress back down to the original size from just before the big bang. Seems like a straightforward problem, right?
Well, that's where the whole thing with "dark matter" comes in. "Dark matter," put simply, is matter that we cannot detect by typical means. Obviously, this puts a significant hurdle in the problem of figuring out whether or not the universe will expand forever or not, because it means we cannot accurately estimate the total mass of the universe.
On April 07 2009 04:49 Xeris wrote: I think the theory of expanding-contracting is more popular than expanding-ripping apart? that the galaxy is expanding and at some point will reach some critical limit and then contract again, like with a rubber band; if you stretch it far enough at some point it's going to snap back to its original position (or just rip I guess)....
don't know which is correct (if any of them are) O_O!
As I understand it (and I am by no means an expert on this subject), the bolded is correct. The reason for that is the gravity of the universe is constantly pulling inwards on itself, causing the expansion to occur at a decelerating rate. I could be wrong though.
However, whether or not the universe will contract is dependant on more than just the decelerating rate. It's also dependant on how fast the universe is expanding currently, as I mentioned above.
Is it correct for me to interpret the big bang as something like an infinitely small spinning point, that suddenly explodes in mass, spinning out matter/energy in all directions outward from it's center point?
No. The universe is expanding and if you calculate back everything it came from one single point. It's not a singularity that exploded or spewed out matter. The universe isn't expanding right now because the outer shell of stars is being thrown away from the center. No, the space between the stars is increasing. Ignore the matter in the universe itself. The universe itself inflated from a single point into what it is now. During all that time a lot happened to the matter inside the universe. But that's a different issue.
I thought that scientists were unable to find like 98% of the matter than the universe ought to have and just theorized something they decided to call dark matter as a temporary explanation.
My question is: Why do physicists or whoever think that the universe won't slow down again?
If there is enough matter in the universe then all that matter has enough mass, causing enough gravity, to make it contract again.
Currently the universe is expanding at increasing velocity and it doesn't look like it has anywhere close to enough to start to contract.
Is it correct for me to interpret the big bang as something like an infinitely small spinning point, that suddenly explodes in mass, spinning out matter/energy in all directions outward from it's center point?
No. The universe is expanding and if you calculate back everything it came from one single point. It's not a singularity that exploded or spewed out matter. The universe isn't expanding right now because the outer shell of stars is being thrown away from the center. No, the space between the stars is increasing. Ignore the matter in the universe itself. The universe itself inflated from a single point into what it is now. During all that time a lot happened to the matter inside the universe. But that's a different issue.
I thought that scientists were unable to find like 98% of the matter than the universe ought to have and just theorized something they decided to call dark matter as a temporary explanation.
I don't think scientists are able to observe more than 1% of the universe, much less be able to account concretely for 2% of it even.
acceleration: the rate of change of velocity with respect to time speed: how fast an object is moving (the time rate of change of position)
Many people are using versions of the word accelerate incorrectly. Accelerating outwards specifically means to either speed up in the outward direction, or possibly slow down (deceleration aka negative acceleration). Velocity and acceleration are not the same thing -_-
On April 07 2009 05:29 Diomedes wrote: The universe is expanding and if you calculate back everything it came from one single point. It's not a singularity that exploded or spewed out matter.
Then what happened?
The universe isn't expanding right now because the outer shell of stars is being thrown away from the center. No, the space between the stars is increasing.
On April 07 2009 05:30 vAltyR wrote: You know what escape velocity is, right? It's the velocity an object must be travelling in order to ecape the pull of the gravity of any given mass.
We can measure the rate of expansion of the universe (if you want more details, ask), so the theory is, if the universe is expanding faster than its own escape velocity, then it will never compress back down to the original size from just before the big bang. Seems like a straightforward problem, right?
quick interruption here, you may or may not know the answer to this question. the general movement of the galaxies - is it a linear path, or is it curving? it would have to be curving, wouldn't it?
On April 07 2009 06:04 micronesia wrote: acceleration: the rate of change of velocity with respect to time speed: how fast an object is moving (the time rate of change of position)
Many people are using versions of the word accelerate incorrectly. Accelerating outwards specifically means to either speed up in the outward direction, or possibly slow down (deceleration aka negative acceleration). Velocity and acceleration are not the same thing -_-
i learned all about this the last time i had a physics discussion in a blog!
It will either expand "forever" or go back to big bang state~~ It depends on the actual mass of the universe, I remember reading book about this particular subject but my english's too weak to actually talk about this stuff lol
hmm... hehe... this is a very large topic, and depending on who you ask... you could receive different answers.
One of the well thought of theories is inflationary cosmology...
pretty much, an extremely small chunk of stuff is made up of dark matter... dark matter, reaching a certain state dark matters has a negative pressure. According to to Einstein's theory of relativity, gravity is not only changed due to displacement and mass, but also pressure and i think temperature. Since this mass has a greater amount of dark matter, this negative pressure creates an expanding gravitational force, causing a rapid expansion...
however, there is the idea that a set of matter only has to meet a certain set of defined characteristics to follow this expansion, like temp and different fields, and could in fact appear practically anywhere. Entire universes expanding out of universes... its a rather neat concept to visualize.. cant seem to find a pic...
Now, the idea of expansion is also a rather tricky one. planets and matter arnt just floating away, but in fact the space is expanding... let me rephrase that... a rather simple example is say you have a balloon with a grid on it... at each point place a penny, then blow up the balloon. The pennys themselves didnt get larger, but the space it is on did...
Now, the entire "bang" that happened just spread out a common matter. This has been attested to by the fact that there is a uniform electromagnetic wave throughout the universe. The entire universe was uniform. Looking now at the quantum mechanics side of things, the tiny jitters that is seen at the very small is spread out to practically uniform space. Whoever, with the jitters, as the universe cooled, tiny bits of matter began to pull on each and after a crapload of time... we got galaxies and junk ...
now, as the universe gets farther and farther away... some have theorized that the force created by the expanding gravity will slowly fall smaller than the contracting force... which will then pull all of the matter back in and once again start the cycle... and expand, contract, expand, contract... etc...
But, as always, there are more theories... Looking at it from a string theory perspective... the universe we know of is composed on one 3-brane and what caused the the expansion was a collision of our 3-brane with another. However, this has yet to be tested for our way of testing, using electromagnetic radiation, is trapped inside of the 3-brane... there is hope that gravity, being so weak, may actually be able in fact be leaking out of our 3-brane and can be used to test such theories... but... i don have my books atm and cant really explain much farther...
Researchers are hoping that the new Hadron collider will be able to, in fact, validate certain theories... being able to crash large ammounts of mater to tiny speeds may create conditions like the begining of our known universe or can hopefully validate some ideas brought up by string theory...
ack... /ramble i wasnt really planning on writing so much... but if you really want an experts opinion on this subject, and some like it, i would advise you get Brian Greene's book Fabric of the Cosmost. It goes for a great light read before bed
edit: i hope i didnt have to many errors like i said... im away from my books
The problem with the way you describe the phenomenon is the fact that you appear to consider matter to be flying outwards from a central point. According to inflationary cosmology, space itself is expanding like a loaf of raisin bread (the raisins representing galaxies, the bread space-time etc.). This means that all galaxies are moving away from every other galaxy. Space is expanding in every direction. There is no central point away from which matter is moving.
I have to read up a lot on space and time. So I don't have anything to add to that part of the discussion right now. The idea of dark energy is a concept thought up after observing acceleration.
As far as matter is concerned. All mater is unstable. Even black holes evaporate over time according to Hawkins. This is not in the order of billions of years. Add a lot more zeros. So in some models the universe will become empty space with only EM radiation.
Edit: The name Big bang suggests an explosion. But there is nothing kinetic about it. A kinetic explosion could never create space. If an pointlike object would explode it would immediately start caving in again due to gravitation. I feel like the subject is way out of my legaue
On April 07 2009 07:47 Swarmy wrote: The problem with the way you describe the phenomenon is the fact that you appear to consider matter to be flying outwards from a central point. According to inflationary cosmology, space itself is expanding like a loaf of raisin bread (the raisins representing galaxies, the bread space-time etc.). This means that all galaxies are moving away from every other galaxy. Space is expanding in every direction. There is no central point away from which matter is moving.
ok, I have heard this and I do understand it. But the actual matter must be moving away from a central point - or else it should be coming together. Right?
On April 07 2009 07:47 Swarmy wrote: The problem with the way you describe the phenomenon is the fact that you appear to consider matter to be flying outwards from a central point. According to inflationary cosmology, space itself is expanding like a loaf of raisin bread (the raisins representing galaxies, the bread space-time etc.). This means that all galaxies are moving away from every other galaxy. Space is expanding in every direction. There is no central point away from which matter is moving.
ok, I have heard this and I do understand it. But the actual matter must be moving away from a central point - or else it should be coming together. Right?
most common example for this in books is pumping spotted baloon with air, where spots represent galaxys~~you should also check hubble,doppler effect
The answer to your question is very simple: an explosion propelles matter away with a certain acceleration a, if there is no resistance force (like in the vacuum of space), the acceleration a will remain constant and the speed of the expanding matter will increase.
Offcourse this is only 1 view of the universe, its origin and its end, hence the awesome fuel for discussions since noone can know what has happened and what will happen.
I suggest reading a book or some other serious references about it (choices are enourmous, many topics), it may seem boring at first, but it is very compelling once you get into it. And with serious i mean NOT wikipedia, never ever cite it or trust it or use it as a reference.
According to some scientists there exists something called 'Dark Matter' and 'Dark Energy'. Dark Matter, they theorize, accounts for about 20-22% of all the mass in the universe, and Dark Energy accounts for about 70-75% of all the mass in the universe.
We cannot detect either of those, and according to all the tests run (don't ask me how they do it -- this is beyond my scope of knowledge), the visible matter in the universe accounts for about 4-6% of all the mass in the universe.
The reason why they believe that the universe is expanding at a faster rate than it was previously (which goes against the logic that gravity from mass will cause expansion to slow and eventually contract) is that Dark energy, being greater in mass than Dark Matter and visible matter combined, is causing the expansion of the universe at a greater rate than it can be contracted.
Of course, this is all highly theoretical. Dark Matter is the only thing we can indirectly prove, but there's significantly less indirect proof of Dark Energy.
This is sorta off topic but some people talked about Einstein, can someone explain how he figured out the equation? Actually, how do people figure out equations in general? I think it's pretty neat to figure out something that will work for specific things
from what i understand, the universe expanding forever is just 1 theory. i've also heard the theory that it will eventually hit some point and turn around and compact into a point again (pulsating hypersphere), and also that eventually it will just stop and remain at one size.
On April 07 2009 09:27 il0seonpurpose wrote: This is sorta off topic but some people talked about Einstein, can someone explain how he figured out the equation? Actually, how do people figure out equations in general? I think it's pretty neat to figure out something that will work for specific things
On April 07 2009 08:16 Gnojfatelob wrote: The answer to your question is very simple: an explosion propelles matter away with a certain acceleration a, if there is no resistance force (like in the vacuum of space), the acceleration a will remain constant and the speed of the expanding matter will increase.
does the force of gravity no longer matter after a certain distance?
On April 07 2009 08:16 Gnojfatelob wrote: The answer to your question is very simple: an explosion propelles matter away with a certain acceleration a, if there is no resistance force (like in the vacuum of space), the acceleration a will remain constant and the speed of the expanding matter will increase.
does the force of gravity no longer matter after a certain distance?
On April 07 2009 08:16 Gnojfatelob wrote: The answer to your question is very simple: an explosion propelles matter away with a certain acceleration a, if there is no resistance force (like in the vacuum of space), the acceleration a will remain constant and the speed of the expanding matter will increase.
does the force of gravity no longer matter after a certain distance?
The strength of gravity relates inversely with the square of distance. So it gets weaker pretty quickly. It's actually the weakest force.
On April 07 2009 07:47 Swarmy wrote: The problem with the way you describe the phenomenon is the fact that you appear to consider matter to be flying outwards from a central point. According to inflationary cosmology, space itself is expanding like a loaf of raisin bread (the raisins representing galaxies, the bread space-time etc.). This means that all galaxies are moving away from every other galaxy. Space is expanding in every direction. There is no central point away from which matter is moving.
ok, I have heard this and I do understand it. But the actual matter must be moving away from a central point - or else it should be coming together. Right?
No, that's the point of the bread example. The space in between every raisin is increasing, the raisins are essentially stationary.
On April 07 2009 07:47 Swarmy wrote: The problem with the way you describe the phenomenon is the fact that you appear to consider matter to be flying outwards from a central point. According to inflationary cosmology, space itself is expanding like a loaf of raisin bread (the raisins representing galaxies, the bread space-time etc.). This means that all galaxies are moving away from every other galaxy. Space is expanding in every direction. There is no central point away from which matter is moving.
ok, I have heard this and I do understand it. But the actual matter must be moving away from a central point - or else it should be coming together. Right?
No, that's the point of the bread example. The space in between every raisin is increasing, the raisins are essentially stationary.
well.. you could ad an origin.. but any place is just as possible as the last... it would merely be used as a point of reference or place helpful to visualize....
edit: nvmd... i missed the point... if the origin was placed anywhere it wouldnt be for the origin of where the big bang banged
On April 07 2009 09:39 Artosis wrote: from what i understand, the universe expanding forever is just 1 theory. i've also heard the theory that it will eventually hit some point and turn around and compact into a point again (pulsating hypersphere), and also that eventually it will just stop and remain at one size.
On April 07 2009 07:47 Swarmy wrote: The problem with the way you describe the phenomenon is the fact that you appear to consider matter to be flying outwards from a central point. According to inflationary cosmology, space itself is expanding like a loaf of raisin bread (the raisins representing galaxies, the bread space-time etc.). This means that all galaxies are moving away from every other galaxy. Space is expanding in every direction. There is no central point away from which matter is moving.
ok, I have heard this and I do understand it. But the actual matter must be moving away from a central point - or else it should be coming together. Right?
No, that's the point of the bread example. The space in between every raisin is increasing, the raisins are essentially stationary.
ok but then a couple followup questions
1.) why are the raisins essentially stationary? shouldn't they either be moving away from the origin of the big bang, or moving towards the "gravitonical center" of the universe? or have the raisins been stationary since the big bang started? because if that's the case then I have more questions.
2.) what leads anyone to believe that space itself is expanding rather than the "raisins" just moving farther apart? I've looked but can't find any actual explanation of this.
anyhow it doesn't stop expanding due to the laws of entropy, diffusion, and inertia (newton's first law i believe?)
though the last of the three may be invalid in that galaxies might affect the trajectory of other galaxies, i think most galaxies are relatively the same size and/or mass which means that gravitational attraction b/w galaxies will have as muhc of an effect on them as 2 soccer balls attract each other...
also no1 really noes exactly wtf happened w/ the big bang and some ppl say it wasn't a big bang but a little bang and then there was a big bang afterward, etc. u get my point.
"infinitely small spinning point, that suddenly explodes in mass, spinning out matter/energy in all directions outward from it's center point?" nvr heard of that one b4... y was it spinning again?
On April 07 2009 04:43 travis wrote: Like, if the milky way was somewhat near the center, it would have shot out slowly and "quickly" began deceleration. Whereas a galaxy much farther away from us could be likely to still be accelerating, but eventually slowing down, no? Just like if you put some paint in the middle of a paper plate and spun it at an extremely high rate. What is flung out closest to the center decelerates the fastest, and what is flung out the farthest continues to accelerate longer.
Is my understanding of this incorrect anywhere?
it only decelerates cus the paper does... ... ... like i said newton's 1st law, the one about inertia (object in motion will try to stay in motion)
On April 07 2009 11:43 R3condite wrote: i hope u pass the mods recognize ur name test
what?
anyhow it doesn't stop expanding due to the laws of entropy, diffusion, and inertia (newton's first law i believe?)
though the last of the three may be invalid in that galaxies might affect the trajectory of other galaxies, i think most galaxies are relatively the same size and/or mass which means that gravitational attraction b/w galaxies will have as muhc of an effect on them as 2 soccer balls attract each other...
also no1 really noes exactly wtf happened w/ the big bang and some ppl say it wasn't a big bang but a little bang and then there was a big bang afterward, etc. u get my point.
"infinitely small spinning point, that suddenly explodes in mass, spinning out matter/energy in all directions outward from it's center point?" nvr heard of that one b4... y was it spinning again?
well if u examine the universe, everything is spinning. on every scale. so I guess that's just what I like to imagine. obviously I am no physicist but inferring from what I have learned of nature it would make sense that it started from spinning.
I guess that would change what the "big bang" was, in that it wouldn't be so much of a "bang" but rather just a spinning point of stuff that was spinning so fast that everything spun outward
On April 07 2009 04:43 travis wrote: Like, if the milky way was somewhat near the center, it would have shot out slowly and "quickly" began deceleration. Whereas a galaxy much farther away from us could be likely to still be accelerating, but eventually slowing down, no? Just like if you put some paint in the middle of a paper plate and spun it at an extremely high rate. What is flung out closest to the center decelerates the fastest, and what is flung out the farthest continues to accelerate longer.
Is my understanding of this incorrect anywhere?
it only decelerates cus the paper does... ... ... like i said newton's 1st law, the one about inertia (object in motion will try to stay in motion)
well I can't describe a better model than that lol. try forgetting that the paper plate is there. the ball of paint spins on it's own.
or maybe imagine a spinning egg, and then the shell shatters.
On April 07 2009 11:44 travis wrote: more questions:
1.) is light bound by gravity? if so, then how does light have a constant speed?
2.) can't the redshift we observe be because something is happening to the light rather than that space is expanding?
3.) since light moves faster than the universe's expansion - where does light go when it reaches the edge of the universe?
1: light is affected by gravity, but only when the gravity is strong; in most cases light is virtually unaffected. The way Einstein's general relativity was partially confirmed was... they looked along the edge of a large object in space to see if they could see the stars behind it.... according to the geometry, the stars should have been visible along the edge of the large object, but they couldn't see the stars. This was because the light coming from the distant stars which was slated to pass by the large object was pulled towards it like a meteor.
2: Frequency of light (color) very rarely changes aside from a doppler shift.
On April 07 2009 12:12 micronesia wrote: 2: Frequency of light (color) very rarely changes aside from a doppler shift.
but how do we know this when we have no way to test the affects of traveling over such a long distance on light?
It's the most likely scenario... certainly could be wrong, but no reason to believe it based on virtually all prior scientific experimentation in this field. Our modern theoretical formulas also support this claim.
also micronesia do you know why red shift led to the theory of expanding space? rather than just galaxies moving at different velocities?
I think it's a bit of a misconception that they measured the light from some stars, saw that it was redshifted, and then concluded acceleration. I'm not sure exactly how they did it as I haven't investigated it and the one documentary I saw years ago when this was first discovered didn't specify. The only thing that makes sense to me is that they observed the time-dependency of the redshift and noticed that it was essentially getting 'redder' although I'm surprised that there would be a detectable difference over the course of a few days/weeks/months.
just a little note for pondering... since i guess that is what this thread is about...
Space itself can expand at speeds faster than the speed cap, light. (granted speed is the incorrect term). a planet further than this region, therefore, cannot be seen by us, for the light it emits is trapped as it tries to swim through this faster current...
all evidence for an accelerating universe are from distant type Ia supernovae, fitting their magnitudes+doppler shifts to their assumed luminosities. The method works assuming all type Ia supernovae have the same luminosity curves over time (which is a fair assumption due to most of them having similar masses and compositions when they occur). However, recent evidence shows that a carbon-based white dwarf might have a different luminosity curve from, say, a silicon based white-dwarf when it explodes, so this assumption may be false.
On April 07 2009 11:44 travis wrote: more questions:
1.) is light bound by gravity? if so, then how does light have a constant speed?
2.) can't the redshift we observe be because something is happening to the light rather than that space is expanding?
3.) since light moves faster than the universe's expansion - where does light go when it reaches the edge of the universe?
1: light is affected by gravity, but only when the gravity is strong; in most cases light is virtually unaffected. The way Einstein's general relativity was partially confirmed was... they looked along the edge of a large object in space to see if they could see the stars behind it.... according to the geometry, the stars should have been visible along the edge of the large object, but they couldn't see the stars. This was because the light coming from the distant stars which was slated to pass by the large object was pulled towards it like a meteor.
2: Frequency of light (color) very rarely changes aside from a doppler shift.
1: Light is always effected by gravity and as you could have guessed gravity pulls with a force according to the photons mass E=mc^2. This causes gravity doppler shifts and also gravitic lensing and it is very easy to derive this intuitively since otherwise you could destroy or create energy.
What however is only noticeable on very strong gravity fields are the effects described by general relativity's version of gravity.
On April 07 2009 15:12 Rekrul wrote: All men want are holes. Some men find them on earth. Others have to look into outer space.
Pretty sure that the force of attraction of space holes are stronger than the holes on the earth!
EPT
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