Expansion Of Space

[emacneille]

I've recently read through the website:

http://www.cfa.harvard.edu/seuforum/questions/

I had a few questions, and decided to ask the community

 

At one point, it says "Yet SPACE itself can expand faster than the speed of

light."

 

I understand that over great distances, space can be said to be expanding

faster than the speed of light. But is it possible or within the laws of

relativity for a smaller space to expand faster than the speed of light?

It says that the rate of expansion is accelerating. As the rate of

expansion for a given measure, say a cubed foot, accelerates, what will

eventually happen? Will the rate of expansion only approach the speed of light or race past

it?

 

I understand that the red shift Hubble saw is attributed to the expansion

of space itself. What about this expansion causes the frequency of light to

decrease while wavelength increases? is amplitude affected by this process?

 

Does the expansion of space cause electrons to be further in orbit around

their nucleus?

[modest]

I've recently read through the website:

http://www.cfa.harvard.edu/seuforum/questions/

I had a few questions, and decided to ask the community

 

At one point, it says "Yet SPACE itself can expand faster than the speed of

light."

 

I understand that over great distances, space can be said to be expanding

faster than the speed of light. But is it possible or within the laws of

relativity for a smaller space to expand faster than the speed of light?

 

Yes.

 

The "Hubble distance" is the distance over which expansion causes recession at the speed of light. The Hubble constant is the rate at which space expands. The larger the Hubble constant, the smaller the Hubble distance. In other words, the faster the rate of expansion of space, the smaller the distance at which expansion equals the speed of light.

 

It says that the rate of expansion is accelerating.

 

That is the best current model, yes.

 

As the rate of

expansion for a given measure, say a cubed foot, accelerates, what will

eventually happen? Will the rate of expansion only approach the speed of light or race past

it?

 

It is not entirely known if the rate of expansion will continue increasing indefinitely. If it does then eventually the cubic foot will expand, first at the speed of light—then faster. Here is a short description:

This possibility is known as phantom dark energy, and it has the particularly drastic effect that the Universe expands so rapidly the separation between objects becomes infinite in a finite time, known as the big rip. During the late stages, the repulsive force of the dark energy becomes so great that first galaxies, then solar systems, and ultimately even individual atoms are ripped apart by it. This alarming possibility is quite compatible with observations of the effects of dark energy, and indeed even somewhat favoured by them. On the plus side, if a big rip does take place, it will not be for at least 20 billion years.

 

http://www.jrank.org/space/pages/2349/future-Universe.html

 

I understand that the red shift Hubble saw is attributed to the expansion

of space itself. What about this expansion causes the frequency of light to

decrease while wavelength increases? is amplitude affected by this process?

 

Here is an often-quoted quote:

 

Light leaves a galaxy, which is stationary in its local region of space, and is eventually received by observers who are stationary in their own local region of space. Between the galaxy and the observer, light travels through vast regions of expanding space. As a result, all wavelengths of the light are stretched by the expansion of space. It is as simple as that.

 

http://en.wikipedia.org/wiki/Edward_Robert_Harrison

 

Wavelength increases because expanding space stretches the wavelength. Frequency decreases because longer waves take longer arriving between peaks (they are further apart).

 

Does the expansion of space cause electrons to be further in orbit around

their nucleus?

 

No.

 

Gravitational effects are too small over such short distances—there is not enough energy—to cause electrons to jump orbitals. If the cosmological constant increases without bound then this will eventually change and atoms will indeed be ripped apart.

 

~modest

[emacneille]

Gravitational effects are too small over such short distances—there is not enough energy—to cause electrons to jump orbitals.

 

I realize gravitational effects are extremely small on a small scale, certainly too small for us to measure right now. But I wasn't getting at electrons switching orbitals. What I'm wondering is if the expansion of space could move where the orbitals are relative to say, the attraction between a proton and a neutron.

 

According to my most recent leisure reading material, QED, the distance of say the first S orbital is a sphere of the most likely spots an S electron is most likely to be. Or admitting to some of the wavelike properties of electrons, the S orbital is where the greatest concentration of charge lies for an S electron. It seems to me like the expansion of space, if it truly happens everywhere, should be slowly nudging the S orbital itself away from the nucleus. One effect of this would be that H atoms are more easily deionized with time.

 

On the other hand, the distance of the S orbital is a relationship between the attraction of an electron and proton and rotational momentum. So, it also seems to me like orbitals might automatically get closer to the nucleus as space pushes outward through them. But if this is true, then how would the expansion of space ever tear apart atoms?

 

What exactly is expanded space like compared the space that has undergone less expansion? Does more expanded space have less density of background radiation?

 

This possibility is known as phantom dark energy, and it has the particularly drastic effect that the Universe expands so rapidly the separation between objects becomes infinite in a finite time

 

Is the distance between objects said to be infinite if the space between them is expanding faster than the speed of light?

 

Dark energy refers to the spontaneous creation and annihilation of tiny particles. By what mechanism does this lead to the expansion of space?

 

You describe the expansion of space as a gravitational effect. I've read that relativity predicts the expansion of space as a result of gravity. Could you say a little about this?

[emacneille]

PS. My first line is a quote form you. How do you add a quote that has the person's name and date of posting on it?

[Tormod]

PS. My first line is a quote form you. How do you add a quote that has the person's name and date of posting on it?

 

When you hit "Reply" on the post you want to reply to, this happens automatically.

 

Otherwise use the "Multiquote" button to make references to multiple posts.

 

Then you just keep the parts of the text you want to quote.

[emacneille]

When you hit "Reply" on the post you want to reply to, this happens automatically.

woa thanks. I had been hitting reply at the bottom of the page

[HydrogenBond]

If you look at gravity it not only contracts space-time but also induces physics phase changes. For example, the gravity of the earth contracts space-time but is not strong enough to induce nuclear fusion via gravity. We would need the gravity level of a star. The star has a deeper space-time well, and it also allows the physics phase change into nuclear fusion. If we could expand the star thereby expand its space-time, a physics phase change will occur shutting off fusion.

 

Expansion of space-time appears to be connected to only half the gravity effect. It is much more similar to SR, where space-time can contract/expand but one does not expect the matter within a relativistic reference to undergo any physics phase changes. If it did, fast moving objects in the universe, would exhibit unique physics phase signatures, like we see with stars and black-holes, which use the two for one effect of gravity.

 

In expanding space-time, with the one for one, we get space-time effects, but not physics phases changes into things such as new orbital states for atoms such as hydrogen. If matter and gravity were leading, this might be a possible.

[emacneille]

The star has a deeper space-time well, and it also allows the physics phase change into nuclear fusion. If we could expand the star thereby expand its space-time, a physics phase change will occur shutting off fusion

 

If it did, fast moving objects in the universe, would exhibit unique physics phase signatures, like we see with stars and black-holes, which use the two for one effect of gravity.

 

In expanding space-time, with the one for one, we get space-time effects, but not physics phases changes into things such as new orbital states for atoms such as hydrogen. If matter and gravity were leading, this might be a possible.

 

Does these fast moving objects not exhibit physical phase changes that we see in stars? Fusion in the sun can happen under conditions of high pressure (gravity) or temperature (kinetics). There is no reason why fusion couldn't occur outside of the sun's center of gravitude, if enough energy is supplied. It is energy, (with mass included in energy's definition as E=mc^2) in high concentrations that causes the physics phase changes you talk of. Point enough lasers at a point and you might just make a worm hole.

 

What do you mean when you say, "If matter and gravity were leading, this might be possible."

This might help clear up the reason the S orbital of H isn't inching out due to the expansion of space.

 

Is there any distinction between space that was just made and the smaller space that preceded it?

[HydrogenBond]

If we look at gravity, such as in a forming star, there is an impact on the other forces of nature due to the work, pressure, temperature, etc, that gravity will induce. We can isolate any of these gravity induced effects to do the same thing, such as the impact of a laser.

 

Although the contraction of space-time occurs with increasing gravity, the impact on space-time, by itself, does not fully define the impact of gravity. We can't use a relative space-time reference to make a planet appear to have the space-time contraction of a star ( in our reference) to create relative fusion. The effects that cause the physics phases changes are not relative to space-time reference, but are directly related to the other things mass/gravity does, pressure, temperature, etc, which can alter physical states.

[modest]

Sorry it has taken me so long to respond, Emacneille. I've had a lot going on and your post slipped my mind.

 

I realize gravitational effects are extremely small on a small scale, certainly too small for us to measure right now. But I wasn't getting at electrons switching orbitals. What I'm wondering is if the expansion of space could move where the orbitals are relative to say, the attraction between a proton and a neutron.

 

According to my most recent leisure reading material, QED, the distance of say the first S orbital is a sphere of the most likely spots an S electron is most likely to be. Or admitting to some of the wavelike properties of electrons, the S orbital is where the greatest concentration of charge lies for an S electron. It seems to me like the expansion of space, if it truly happens everywhere, should be slowly nudging the S orbital itself away from the nucleus. One effect of this would be that H atoms are more easily deionized with time.

 

On the other hand, the distance of the S orbital is a relationship between the attraction of an electron and proton and rotational momentum. So, it also seems to me like orbitals might automatically get closer to the nucleus as space pushes outward through them. But if this is true, then how would the expansion of space ever tear apart atoms?

 

While space itself is said to expand, it is ultimately the things in space that make it expand. Expansion is a part of gravity and gravity is ultimately caused by mass. Expansion, in other words, is just a way of describing how things want to act under the influence of gravity.

 

The force that gravity imparts on two objects (whether they are two subatomic particles or two planets) depends on three factors: the mass of the objects, the distance between them, and the value of the cosmological constant. If you have a proficiency with math, I can give you the exact relationship:

 

[math]{\Phi}\vec{\nabla}=-{\frac{GM}{r^2}}{\vec{r}}+\frac{c^2{\Lambda}r}{3}{\vec{r}}[/math]

 

when you look at gravity this way you can imagine it having two parts; an attractive part and a repulsive part. Which part is dominant depends on the distance between the objects. Two stars then, that are in the same galaxy, will attract one another gravitationally. But, if those same two stars are much further apart (let's say a billion lightyears) then the gravitational force between them will be repulsive.

 

Over very short cosmological distances (for example, between the sun and the earth) the cosmological constant plays almost no role at all. It contributes almost nothing to the force of gravity. The distance between the nucleus of an atom and its electron is so small that the cosmological constant would have to be huge for gravity at that scale to be repulsive rather than attractive. Also, because subatomic particles have so little mass gravity is extremely weak inside an atom. To actually remove an electron from an atom would therefore mean that the cosmological constant would have to be unimaginably large.

 

Our best gravitational model of the universe, the FLRW model, does indeed predict that the cosmological constant will increase infinitely. The acceleration of expansion will continue without bound. So, it is possible that at some point in the future atoms will be ripped apart by gravity. Currently, however, this is very, very far beyond the scope of gravity's strength.

 

What exactly is expanded space like compared the space that has undergone less expansion?

 

Expansion is just a convenient way of saying that the distance between objects increases in a manner proportional to their distance. As space expands, distances over cosmic scales increase.

 

Does more expanded space have less density of background radiation?

 

Yes.

 

Is the distance between objects said to be infinite if the space between them is expanding faster than the speed of light?

 

No. If a car is moving away from a person (as an example) at twice the speed of light then after 3 years it will be 6 lightyears away.

 

Dark energy refers to the spontaneous creation and annihilation of tiny particles. By what mechanism does this lead to the expansion of space?

 

The similarities between quantum fluctuations and the negative pressure of the cosmological constant (ie dark energy) is explained rather well here: http://www.astro.ucla.edu/~wright/cosmo_constant.html

 

You describe the expansion of space as a gravitational effect. I've read that relativity predicts the expansion of space as a result of gravity. Could you say a little about this?

 

That's funny. I wrote the bit above about expansion being gravitational before I read this.

 

The expansion of space is based on a model called Lambda-CDM which is a solution to a metric called FLRW which is an exact solution of general relativity, which is, a theory of gravity. In its most basic form then, the "expansion of space" is a way of saying how a homogeneous collection of matter wants to act under the influence of gravity alone. The forces that would cause the universe to expand are really no different from the forces that cause stars to collapse. It is gravity. According to Einstein's general relativity, gravity can be repulsive if the cosmological constant term is non-zero. Currently, this is only apparent over large cosmological distances.

 

A good wiki article would be: http://en.wikipedia.org/wiki/Metric_expansion_of_space

 

~modest