# The expansion of space-time

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#### Jerromy

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I'm mulling a thought around my head about the expansion of space...

It seems that there is no known cause of gravity that has been proven to my knowledge. No "gravitons" have ever been found, no connection to any other forces like electricity and magnetism, no known "opposite" force or balancing system to speak of. The only thing we really know is everything is attracted to anything else.

In my less than calculus but better than average mathematical mind I had a light bulb blink on relating to the expansion of space being a possible counter force to the attraction of matter within that space. Not having the formal education nor the experience in calculus required to simplify an equation that could possibly prove the relationship is frustrating.

Basically what I am implying is that the force of gravity attracting matter is what would be driving the expansion of the space around it. I am not saying that "the deeper the well of gravity the faster space expands", I am saying "the larger masses attracting expands space around then"

Picture if you will, our galaxy and our approaching neighbor. Over the course of the next how ever many millions of years we will be attracting each other exponetially faster as the gravity gets stronger between us. As matter is accelerated it's mass increases and as that mass increases the attraction would rise faster than proximity alone. As the energy density within our combined "space" increases would it not make sense that "space" would be displaced?? As I stated earlier I'm not in the habit of calculating cosmological equations and my busy life leaves little room to ponder let alone prove theories but perhaps someone might make sense of this thought of mine and see if there is any plausible relationship. I haven't given it a whole lot of thought yet but I'm hoping others may brainstorm this with me.

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#### ramparts

##### Guest
Hi Jerromy. Thanks for your post

Jerromy":qriah7es said:
I'm mulling a thought around my head about the expansion of space...

It seems that there is no known cause of gravity that has been proven to my knowledge. No "gravitons" have ever been found, no connection to any other forces like electricity and magnetism, no known "opposite" force or balancing system to speak of. The only thing we really know is everything is attracted to anything else.

In fact, we do know the cause of gravity - or at least, we have a very good description of it. Matter and energy - "stuff", if you will - causes space itself to bend, and when objects follow straight paths in curved space, the paths are also curved. That's gravity. Think of an object travelling along the surface of a sphere - there are no "straight lines", what looks to it like straight lines look to us (from the outside) like circles.

In my less than calculus but better than average mathematical mind I had a light bulb blink on relating to the expansion of space being a possible counter force to the attraction of matter within that space. Not having the formal education nor the experience in calculus required to simplify an equation that could possibly prove the relationship is frustrating.

Unfortunately it takes calculus and a whole lot more for math to be very useful in modern physics - I'm about to graduate college with a physics degree and I still lack a lot of the necessary background (grad school, grad school...).

Basically what I am implying is that the force of gravity attracting matter is what would be driving the expansion of the space around it. I am not saying that "the deeper the well of gravity the faster space expands", I am saying "the larger masses attracting expands space around then"

Picture if you will, our galaxy and our approaching neighbor. Over the course of the next how ever many millions of years we will be attracting each other exponetially faster as the gravity gets stronger between us. As matter is accelerated it's mass increases and as that mass increases the attraction would rise faster than proximity alone. As the energy density within our combined "space" increases would it not make sense that "space" would be displaced?? As I stated earlier I'm not in the habit of calculating cosmological equations and my busy life leaves little room to ponder let alone prove theories but perhaps someone might make sense of this thought of mine and see if there is any plausible relationship. I haven't given it a whole lot of thought yet but I'm hoping others may brainstorm this with me.

Well, I'm a bit confused. Matter attracts other matter - so how would the expansion of the universe (where everything moves away from each other) be caused by that attraction?

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#### Erevna

##### Guest
I enjoy these thought experiments also. My story is one I don't recommend others to follow. At 16, I found out that Astronomers made, on average, \$1600/month in 1984 (pre-Hubble days). I wanted to be an Astronomer since I was 4...loved it. Ended up with a Bachelors in Electronics..boorrriiinnggg. I’ve eyeball University of Texas Astronomy program, it's pretty good...after winning the lottery, I'm in!

Anyway, not being an Astrophysicist, I have the same issue with lack of education. But as far as gravity, I've wanted to ask "Why we call it a force anyway?" As was stated, it's more an effect of the warping of space-time. Strong/Weak/Electromagnetic forces have force carriers. With gravity, we already know what it is, what causes it...why would we need force carriers? The way gravity is explained to us "lay" persons; it's more a "cause-effect".

A bit off the gravity subject, but I have a question about Neutron stars. I've wondered what is the physics that creates the ultra-high magnetic forces. Do neutrons carry an electric charge? Do neutron stars have polarity? I'm a bit confused and if anyone can take a stab, Id appreciates it. By the way, I did take calculus II (20 years ago)...not that I care to do any math just yet.

Thanks...Erevna (Researcher for Truth)

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#### michaelmozina

##### Guest
Erevna":18529cs9 said:
Anyway, not being an Astrophysicist, I have the same issue with lack of education. But as far as gravity, I've wanted to ask "Why we call it a force anyway?" As was stated, it's more an effect of the warping of space-time.

FYI, those who are into GR tend to use your definition of gravity rather than the term 'force'. Laziness (and a respect for QM) often causes me to use the term force, but typically I think of gravity in terms of GR and I perceive gravity as a distortion of space/time.

Strong/Weak/Electromagnetic forces have force carriers. With gravity, we already know what it is, what causes it...why would we need force carriers? The way gravity is explained to us "lay" persons; it's more a "cause-effect".

Well, that depends on whether or not you believe a "grand unified theory'' and have some faith in QM not just GR. In QM the carrier particle of gravity is thought to be the hypothetical graviton. The "cause/effect" relationship is different in QM than it is in GR.

A bit off the gravity subject, but I have a question about Neutron stars. I've wondered what is the physics that creates the ultra-high magnetic forces.

Good questions.
http://www.astro.umd.edu/~miller/nstar.html

Do neutrons carry an electric charge?

The outer "crust" is thought to be composed of mostly iron and nickel atoms that have been stripped of all their electrons. That crust could carry a positive charge, but not the neutron core itself.

Do neutron stars have polarity?

A magnetic polarity, yes. It's typically related to it's axis of rotation.

I'm a bit confused and if anyone can take a stab, Id appreciates it. By the way, I did take calculus II (20 years ago)...not that I care to do any math just yet.

Thanks...Erevna (Researcher for Truth)

Welcome to the board by the way.

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#### michaelmozina

##### Guest
Jerromy":djmfww1v said:
I'm mulling a thought around my head about the expansion of space...

It seems that there is no known cause of gravity that has been proven to my knowledge. No "gravitons" have ever been found, no connection to any other forces like electricity and magnetism, no known "opposite" force or balancing system to speak of. The only thing we really know is everything is attracted to anything else.

The quest for a grand unified field theory and a link between the EM field and gravity continues. It's a bit premature IMO to 'assume' there's no connection IMO.

As you get time to study GR, you'll discover that the "cause" of gravity is due to the fact that material objects "bend/curve/warp" space-time around themselves. The "attraction" between objects is a curvature related to the bending of the space/time continuum around the material objects.

The notion of an expanding "space" is a bit of a misnomer IMO. While expansion between objects may occur, the notion of expanding "space" is still a question of debate. There are a number of papers and counter papers on this topic and the ball is I believe now in this author's court. While expansion is probable, the expansion of space is still somewhat 'debatable'.

http://arxiv.org/abs/astro-ph/0601171

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#### Erevna

##### Guest
michaelmozina: Thanks for the neutron star thread. Just what the doctor ordered!

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#### ramparts

##### Guest
While we don't yet have a solid theory of quantum gravity, we know one has to exist - otherwise things like the early universe and the centers of black holes aren't governed by the laws of physics Also, the graviton hasn't been discovered yet, but there's really no reason to believe it won't some day. In quantum field theory, any field (including the gravitational field) is considered to be composed of particles, and it would be very weird - very interesting, too! - if gravity didn't follow that rule. Also, gravitational waves (which, like light waves and photons, are closely linked to gravitons) are a standard prediction of GR even without the quantum effects. Hopefully those will be detected in the next few years, there are experiments (LIGO and LISA) underway.

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#### benbald

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ramparts":38q4k6e6 said:
While we don't yet have a solid theory of quantum gravity, we know one has to exist... Also, the graviton hasn't been discovered yet, but there's really no reason to believe it won't some day.

People used to say this exact same thing about the aether. Michelson wasn't trying to prove that the aether didn't exist, he was trying to measure it! And look at all we've learned as a result. So just because our current models and theories say something should exist, definitely doesn't mean that it will. It just gives us another way to prove ourselves wrong, thus enabling new ideas and new growth. I, for one, love it when we prove ourselves wrong.

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#### Jerromy

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ramparts":7u527092 said:
Hi Jerromy. Thanks for your post

ramparts":7u527092 said:
Think of an object travelling along the surface of a sphere - there are no "straight lines", what looks to it like straight lines look to us (from the outside) like circles.

I can conceive how something (like a "flat" surface) can be curved by gravity and the light with which we view it can be "bent" in the same curvature and appear straight to the observer. Not quite the same as being on the surface of a large sphere, I mean in the sense of gravitational lensing... the light we observe past the edge of an event horizon could in reality be curved far from straight but still appear straight.

ramparts":7u527092 said:
Well, I'm a bit confused. Matter attracts other matter - so how would the expansion of the universe (where everything moves away from each other) be caused by that attraction?

That is exactly what I am trying to figure out. From the best I can gather as plausible from many conflicting theories, the universe we see around us inflated faster than the speed of light for some period of time >0. Then some millions of years later hydrogen started to attract into clusters which ignited. After some time of fast burning stars producing heavier elements, galaxies started to gather and eventually groups of galaxies merged. Now here we are some supposed 13.7 billion years later and all I see is evidence that not only is the universe still expanding but it is accelerating as well.

Either something that would look amazingly simple from some outside observation point is tricking us in to concluding this or something is driving this acceleration by the simple assumption that "cause and effect" are still relevant logical physical attributes of our existence.

If the latter is the case, I am inclined to believe that if space is curved "into" mass then the opposite effect in the absence of mass would be space curving "outward". Basically the concept I'm trying to convey is that space is displaced by the presence of mass and therefore would be diffused outward by the convergence of matter.

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#### ramparts

##### Guest
benbald":3m2e1kgj said:
ramparts":3m2e1kgj said:
While we don't yet have a solid theory of quantum gravity, we know one has to exist... Also, the graviton hasn't been discovered yet, but there's really no reason to believe it won't some day.

People used to say this exact same thing about the aether. Michelson wasn't trying to prove that the aether didn't exist, he was trying to measure it! And look at all we've learned as a result. So just because our current models and theories say something should exist, definitely doesn't mean that it will. It just gives us another way to prove ourselves wrong, thus enabling new ideas and new growth. I, for one, love it when we prove ourselves wrong.

Right, so what the aether argument tells us is that we shouldn't assume our theories are correct before they have significant experimental verification. What the aether argument is often used to suggest, and incorrectly, is that we don't actually know anything and all things are equally possible. I'm not sure if that's what you're saying, but it definitely seems like you're not giving our current theories enough credit. The better developed a theory is, and the more experimental verifications it's had in some sectors, the higher the probability that the unverified predictions of that theory will also be correct. Both GR and quantum field theory have, separately, made remarkably robust predictions, and have yet to get a single prediction wrong.

Note that I did say it would be very interesting if the graviton (or gravitational waves) was found not to exist - that would open up lots of really fascinating doors for physics. But the likelihood of such a thing being true is remarkably low, and far lower than the probability 100+ years ago of the aether being wrong.

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#### benbald

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Agreed.

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