Gravity?

[Joerg]

Ok from my understanding of gravity it is alot like a dent in space and the matter sort of slides into these dents created by great masses of matter. But that still doesnt help me much. I would like a better ansewer as to what is gravity like what causes it? An energy? If so how fast does it react? The speed of light or faster or even instant? And the next questions is if gravity is like dents in space then wouldnt galaxys fall towards each other instead of the doppler effect causing them to pull away from each other?

 

[CycloWizard]

I believe Einstein described gravity as the curvature of space. I can't remember too much about his theories relating to it, though I think the amount of curvature is related to the mass in the area.

 

[bigal40]

Originally posted by: Joerg
Ok from my understanding of gravity it is alot like a dent in space and the matter sort of slides into these dents created by great masses of matter. But that still doesnt help me much. I would like a better ansewer as to what is gravity like what causes it? An energy? If so how fast does it react? The speed of light or faster or even instant? And the next questions is if gravity is like dents in space then wouldnt galaxys fall towards each other instead of the doppler effect causing them to pull away from each other?

I think that one of the theories as to why the galaxies are expanding out away from each other is that they are still being propelled from the Big Bang and that it is possible for them to eventual slow to a stop and the start moving back in towards each other eventually causing another extremely dense clump of matter and then exploding again in another big bang

 

[cquark]

Originally posted by: Joerg
Ok from my understanding of gravity it is alot like a dent in space and the matter sort of slides into these dents created by great masses of matter. But that still doesnt help me much. I would like a better ansewer as to what is gravity like what causes it? An energy?

Energy and mass both cause spacetime to curve.

If so how fast does it react? The speed of light or faster or even instant?

Gravitational impulses travel at the speed of light, so we wouldn't notice the Sun if it disappeared for a little over 8 minutes...

And the next questions is if gravity is like dents in space then wouldnt galaxys fall towards each other instead of the doppler effect causing them to pull away from each other?

Galaxies do fall toward each other. The Milky Way is falling toward Andromeda and will collide with that galaxy in a couple of billion years. The Milky Way is currently colliding with the Saggitarius Dwarf Galaxy on the other side of the spiral from us, and the entire Local Group is falling toward the great attractor in the direction of the Virgo Supercluster.

The cause of the universe's expansion is the Big Bang. It's not history; it's an ongoing event. Galaxies and clusters thereof are getting farther apart on average due to the expansion of the universe, but some galaxies are close enough to each other that their attraction outweighs the universal expansion. As for the Doppler effect, it's a side-effect of the expansion, not a cause.

 

[Joerg]

Ok so if gravitational forces travel at the speed of light then wouldnt most of the universe be contracting due to the enormous mass of whatever was before the big bang due to the fact that the change in gravity would not have effected? If the universe is really 20billion years old then anything beyond 20billion light years away from the former object that caused the big bang would be effected by an amount of gravity equivalent to the mass of everything in the universe.

Non related question but after checking on the age and size of the universe how is it possible that the universe is 156billion light years wide and only 20 billion years old wouldnt that mean that objects emitted from the big bang had to travel around 4.375 times the speed of light to reach the edge of the known universe.


Lol im to curious at times.

 

[cquark]

Originally posted by: Joerg
Ok so if gravitational forces travel at the speed of light then wouldnt most of the universe be contracting due to the enormous mass of whatever was before the big bang due to the fact that the change in gravity would not have effected? If the universe is really 20billion years old then anything beyond 20billion light years away from the former object that caused the big bang would be effected by an amount of gravity equivalent to the mass of everything in the universe.

The term "before the Big Bang" doesn't have any meaning. The Big Bang is the creation of spacetime itself, not the emergence of matter/energy within a pre-existing spacetime; there was no space or time "before" it since there was no concept of before.

Non related question but after checking on the age and size of the universe how is it possible that the universe is 156billion light years wide and only 20 billion years old wouldnt that mean that objects emitted from the big bang had to travel around 4.375 times the speed of light to reach the edge of the known universe.

Good question. The universe expanded faster than the speed of light during the inflationary era, which actually doesn't violate relativity, which forbids the transfer of information/matter between two entities faster than light. The expansion of spacetime doesn't transfer any information or matter; in fact, nothing's moving either--there's just more space between objects than there was before.

 

[unipidity]

Gravity does act to slow the rate of expansion of the universe... but 'dark energy' acts to increase it.

And no, I dont know what dark energy is. Unless you want a trite answer like 'the cosmological constant'. It doesnt appear to be vacuum energy, which is far too powerful. Or maybe our quantum is crap due to a lack of decent mathematicians.

 

[Joerg]

Hmm so is it scientifically shown that there was nothing before the big bang? I kind of find it hard to believe that the big bang is the beginning of everything. Ive always held the opinion that the big bang was the result of all the matter in a previous universe colliding into a massive ball or somthing like that and finnally culminating into a massive release of energy and matter. Sort of black holes eating each other until everything is all in one. Not saying im right just wondering.

And thanks for all the info.

 

[cquark]

Originally posted by: Joerg
Hmm so is it scientifically shown that there was nothing before the big bang?

Again, you can't use the term "before" with any meaning there, but yes, the Big Bang is the origin of spacetime and its subsequent expansion. The universe is analogous to the surface of an expanding balloon, so there's no edge though it is finite.

 

[imported_jb]

i dunno. i still believe that big bangs are a repeated event. i don't think there is proof they aren't. seems like it still gets all pretty theoretical once you start talking "pre-big bang" and multiverses and such.

 

[Joerg]

I have to agree with jb i really just dont see how science can justify saying that there is no pre big bang. I mean i understand that it could be the beginning of everything we know such as the properites of matter and stuff specific to this universe but i dont think that this universe is the one and only and i wouldnt doubt that before the end of our life times we will see evidence that the universe will one day shrink in upon itself and again collapse.

 

[bsobel]

Another current theory, appeals to me at some basic level (burst of matter, expansion until matter effectively is so spread out that the universe is void and the process can repeat within the context of the existing universe)

Here...

 

[f95toli]

Science can't say anything about what happened "before" (we have to be carefull about how we use this term) Big Bang, it IS possible that we live in a cyclic univsere which expands and then collapses over and over again. However it is doubtfull if we will ever be able to tell wheter or not this is actually the case, current theories can't tell us anything but MAYBE string theory will eventually be able to tell us wheter or not it MIGHT be true or not.

Btw, the age of the universe is 13.8 billion years (I don't remember the margin of error, +-0.2 billion years or so) and if I remember correctly the radius is something like 40-50 billion light years.

 

[cquark]

I have to agree with jb i really just dont see how science can justify saying that there is no pre big bang. I mean i understand that it could be the beginning of everything we know such as the properites of matter and stuff specific to this universe
...
(burst of matter, expansion until matter effectively is so spread out that the universe is void
...

Again, this seems to be the core misunderstanding that I've seen in several posts, that the Big Bang is an energy/matter explosion like those of our everyday experience but on a grander scale.

The Big Bang is the expansion of spacetime; you can't separate space from time. If the universe had a zero size, it necessarily also had zero time. The expansion is accelerating and there's far too little matter/energy for gravity to reverse the expansion. There's not going to be a collapse, which would probably be for the best as that would imply time going backwards too.

As for other universes, that's pure speculation. By definition, we can't observe them, so yes, they could exist, but it's not something science can speak to.

 

[silverpig]

Asking what came before the big bang is sort of like asking what time your watch read before it was manufactured.

 

[imported_jb]

omg... just because there is no arm to put a watch on doesn't mean that time isn't happening at 1000ms/s.

 

[Machupo]

Originally posted by: silverpig
Asking what came before the big bang is sort of like asking what time your watch read before it was manufactured.

not a cogent relation...

a watch is a device used to give people a meter of an ongoing happenstance like time whereas for all intents and purposes the big bang WAS the beginning of time (or our frame of reference relating to it, depending on your philosophical bent)

i understand what you were trying to get at whereas there cannot be something before nothing, but watch allusions lead to comments like:

omg... just because there is no arm to put a watch on doesn't mean that time isn't happening at 1000ms/s.

the whole idea of a initial singularity means that all mathematical equations are moot... no information can be passed through a singularity (across the face, possibly, but not through) so it doesn't really matter whether anything existed or didn't exist before the big bang, it's out of our universal frame of reference

as for a ciclic universe, the brane theory lets me sleep better at night as opposed to ideas of a big crunch and the associated causality violations :Q


the basics of it are that if the information requires that you cross a singularity or any other equation that deals in hefty amounts of infinity, then why even bother? you aren't going to get anything but rubbish. now, re: branes, if equations could be modified to take into account having a parallel state less than the width of a proton in a previously unexplored dimension (read dimension as direction of measurement, not as the science fiction type), then you could theoretically pass information across the gap, but you will never get information from before the "impact" as the universe was necessarily at a zeroized state.

one point that i'm interested by is that the brane idea conveniently "explains" hyperinflation in the early universe... possibly actual contact between the two gravitational "dents"? that would take an immense amount of intertia, for sure!

 

[xSauronx]

Originally posted by: bsobel
Another current theory, appeals to me at some basic level (burst of matter, expansion until matter effectively is so spread out that the universe is void and the process can repeat within the context of the existing universe)

Here...

too tired to read it all tonight, but im bookmarking it, interesting

 

[Joerg]

Ok i understand that time for this universe begins after the bigbang and there for from our universes perspective there is no before the big bang becuase that is the point of orgin for time and space. But what i cant understand is any scientific explanation of why there can be no before big bang from any perspective. That seems to lead us to a dead end at sort of the point saying god created the heavens and the earth type of thing.

I know that im going to keep getting the same ansewer if i continue to question about post big bang so i guess i will just leave it where it is now. The new question is if the big bang stretched space and time then couldnt one of the other be some how inversely stretched in effect making the distance or the time between 2 points much smaller enabling a speed greater than light?

 

[cquark]

Originally posted by: Joerg
Ok i understand that time for this universe begins after the bigbang and there for from our universes perspective there is no before the big bang becuase that is the point of orgin for time and space. But what i cant understand is any scientific explanation of why there can be no before big bang from any perspective.

Your reasoning still sounds like it's based on the idea that spacetime is something separate from the universe, so you could just change your coordinate system or move outside of the universe to observe its formation. The problem is that there is no outside.

In fact, that's the essential difference between nonEuclidean and Euclidean geometries. For there to be a curve in Euclidean geometry, there has to be an extra dimension for the object to be curved through. That's not the case in nonEuclidean geometries, like the Riemannian geometry of general relativity. Gravity curves four-dimensional spacetime, but there is no fifth dimension.

The new question is if the big bang stretched space and time then couldnt one of the other be some how inversely stretched in effect making the distance or the time between 2 points much smaller enabling a speed greater than light?

Shrinking the space between two points wouldn't increase your speed, but it woul decrease the distance between the two points for anyone travelling between them. In theory, such a warp drive is possible, and papers have been written on it, but we can't produce objects with sufficient density to create such a device. You'd need at least nuclear densities on a large scale and the problem is that nuclei are unstable due to the short range of the strong force; that's why elements after 100 or so last milliseconds at best, and we'd need to construct something containing 10^20 plus nuclei.

 

[Jeff7]

Gravitational impulses travel at the speed of light, so we wouldn't notice the Sun if it disappeared for a little over 8 minutes...

If gravity travelled faster than light, it would be possible to communicate fairly easily faster than light.

I think that one of the theories as to why the galaxies are expanding out away from each other is that they are still being propelled from the Big Bang and that it is possible for them to eventual slow to a stop and the start moving back in towards each other eventually causing another extremely dense clump of matter and then exploding again in another big bang

I've read more often now that there's not enough matter in this universe to pull it all back together again; it'll likely continue to disperse indefinitely.

As for other universes, that's pure speculation. By definition, we can't observe them, so yes, they could exist, but it's not something science can speak to.

And ultimately, irrelevant - it's probably outright impossible to get "outside" this Universe's realm of spacetime. Whatever is outside the balloon, maybe there's other universes all over the place. But there's simply no way of them interacting, ever.

 

[Generic Moniker]

Originally posted by: Jeff7

Gravitational impulses travel at the speed of light, so we wouldn't notice the Sun if it disappeared for a little over 8 minutes...

If gravity travelled faster than light, it would be possible to communicate fairly easily faster than light.

Seeing that no one has measured a graviton, I would hardly characterize the above communication as fairly easily.

 

[cquark]

Originally posted by: Generic Moniker
Seeing that no one has measured a graviton, I would hardly characterize the above communication as fairly easily.

Fair enough, LIGO isn't an easy detector and artificially creating detectable gravity waves would be even harder.

 

[silverpig]

Originally posted by: Machupo

Originally posted by: silverpig
Asking what came before the big bang is sort of like asking what time your watch read before it was manufactured.

not a cogent relation...

a watch is a device used to give people a meter of an ongoing happenstance like time whereas for all intents and purposes the big bang WAS the beginning of time (or our frame of reference relating to it, depending on your philosophical bent)

i understand what you were trying to get at whereas there cannot be something before nothing, but watch allusions lead to comments like:

Actually my relation works fine. The universe is one big clock. Its ongoing happenstances provide a measure of time. There was no universe before they big bang, hence no watch. It works fairly well.

 

[Machupo]

Originally posted by: silverpig

Originally posted by: Machupo

Originally posted by: silverpig
Asking what came before the big bang is sort of like asking what time your watch read before it was manufactured.

not a cogent relation...

a watch is a device used to give people a meter of an ongoing happenstance like time whereas for all intents and purposes the big bang WAS the beginning of time (or our frame of reference relating to it, depending on your philosophical bent)

i understand what you were trying to get at whereas there cannot be something before nothing, but watch allusions lead to comments like:

Actually my relation works fine. The universe is one big clock. Its ongoing happenstances provide a measure of time. There was no universe before they big bang, hence no watch. It works fairly well.

right, i understand, and i agree with you... the point i was making is that a watch does not create time, it merely measures a currently occuring event, whereas the universe was the "creation" of time

small point, i admit, it also matters on your frame of reference... if you didn't know that "time" was ongoing, than the creation of a watch may indeed lead you to believe that you have created time.