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sethoscope
2008-Nov-25, 12:28 PM
Ok I'm trying to get my head around the expansion theory and I think I'm starting to get somewhat closer. But the more I understand the more questions arrise.

Soooooo..... The space between galaxies is expanding and thus we see the redshift of galaxies some of which are receeding from us past the Hubble distance or faster than the speed of light. This space is expanding but not expanding into or out of anything necessarily. Since this is expansion of space and not something moving through space it's different. Is there any way to calculate the energy needed to facilitate this type of expansion? Does it require energy? How much? Can it be measure? How?

Please free to address these questions or correct anything that I've stated above that is wrong.

Thanks for your help.

Cougar
2008-Nov-25, 02:11 PM
Is there any way to calculate the energy needed to facilitate this type of expansion? Does it require energy? How much? Can it be measure? How?

Whoever figures this out will probably be receiving a Nobel. There is apparently some (very small) energy content of "empty" space that results in more space being produced "in between" existing space very, very slowly. Quantum theorists have looked at virtual particle creation occurring in empty space, or the uncertainty principle, or both, and they have come up with a calculation for the energy content of empty space. Trouble is, this calculation has come to be known as the mother of all miscalculations, resulting in an estimate that is 10120 times larger than the amount observed. Speculators suggest there is some symmetry or principle that "cancels out" such a large number almost completely, but not quite... leaving us with the miniscule amount of expansion going on in the universe. (It only becomes noticeable when you start accumulating millions and billions of lightyears of the stuff.)

Spaceman Spiff
2008-Nov-25, 03:15 PM
I may be wrong, but I think the question was more generic, with regards to expanding space-time, than the effect of accelerated expansion due to some unknown "dark energy".

Cougar
2008-Nov-25, 03:54 PM
I may be wrong, but I think the question was more generic, with regards to expanding space-time, than the effect of accelerated expansion due to some unknown "dark energy".

Spiff wrong? Unlikely.

I tend to confuse expansion and acceleration, or lump them together, because of their apparent tight relationship. Are their mechanisms separate and different? I guess that's a tough question since the mechanism of dark energy is completely unknown.... Do we really even know the "mechanism" behind the expansion of the universe? I guess it has always just been presumed to be "outward momentum," but.... does that really fit?

01101001
2008-Nov-25, 04:10 PM
I may be wrong, but I think the question was more generic [...]

Let's ask. sethoscope: About what expansion do you ask? What part of this picture? The initial rapid inflation? The more linear expansion that followed? The more recent acceleration?

NASA Wilson Microwave Anisotropy Probe (WMAP): Timeline of the Universe (http://map.gsfc.nasa.gov/media/060915/index.html)

http://map.gsfc.nasa.gov/media/060915/060915_320.jpg (http://map.gsfc.nasa.gov/media/060915/index.html)

sethoscope
2008-Nov-25, 05:27 PM
[QUOTE=01101001;1373364]Let's ask. sethoscope: About what expansion do you ask? What part of this picture? The initial rapid inflation? The more linear expansion that followed? The more recent acceleration?

Thanks for your responses. Yes I do believe my question was a bit more generic.

So there really was no big explosion and thus the term Big Bang is a bit misleading. However movement usually requires energy in some form or another (ect. kinetic, potential, thermal, gravitational, sound . . . ) I guess I was asking is there any theories or ideas about what is fueling the expansion including the initial rapid inflation, the linear expansion and the recent acceleration? Perhaps this gets into muliverse theories. Regardless of where the energy is coming from is it correct to say that a huge amount of energy is being used, or converted, by the Universe in it's expansion? Can the amount of energy be calculated?

This may not even be a realistic question and perhaps I'm just missing a piece of the puzzle.

Thanks for your patience!

Spaceman Spiff
2008-Nov-27, 03:36 AM
The short answer to each of the questions (http://www.bautforum.com/questions-answers/81649-expanding-universe-energy-question.html#post1373239) is that we do not yet know. There are proposed models, in various stages of development and with various amounts of observational evidence. Here is a reasonably accurate overview (with no mathematical details and few details of any sort), and while I am a professional astronomer, I have no expertise in inflationary cosmology. Some of the more salient points are in bold.

The standard (http://en.wikipedia.org/wiki/Lambda-CDM_model) big bang (http://en.wikipedia.org/wiki/Big_Bang) model, whose foundations are General Relativity (http://en.wikipedia.org/wiki/Introduction_to_general_relativity) and Hubble's Law (http://en.wikipedia.org/wiki/Hubble%27s_Law), does not deal with initial conditions. The simple FLRW (http://en.wikipedia.org/wiki/Friedmann-Lema%C3%AEtre-Robertson-Walker_metric) solutions to the Einstein's field equations are made so by the underlying assumptions of isotropy and homogeneity of matter and energy. Space-time filled with such a "fluid" of matter-energy will expand (or contract) given the slightest nudge, and all observers at rest with respect with the flow (co-moving observers) will measure Hubble's Law. Expansio (http://en.wikipedia.org/wiki/Metric_expansion_of_space)n (or contraction) usually means simply that the matter-energy content (on distance scales over which this stuff is homogeneous) becomes more dilute (or concentrated) with time. Picture it like this (http://www.atlasoftheuniverse.com/bigbang.gif). Go here (http://www.atlasoftheuniverse.com/bigbang.html), here (http://www.atlasoftheuniverse.com/redshift.html), and here (http://www.astro.ucla.edu/%7Ewright/cosmology_faq.html) for more help (for starters) for the layman. You might find this paper (http://arxiv.org/abs/0707.0380) enlightening (some parts are a bit technical, but much of it is accessible to the non-specialist). And finally, the Scientific American article, Misconceptions of the Big Bang (http://www.mso.anu.edu.au/%7Echarley/papers/LineweaverDavisSciAm.pdf), is an excellent starting place for the beginner.

These solutions (http://en.wikipedia.org/wiki/Friedmann_equations) are nothing more than equations of motion for this fluid of matter-energy as a function of time. Depending on the nature of the constituents of this fluid (normal matter of protons, neutrons and electrons, photons and neutrinos, dark matter (http://en.wikipedia.org/wiki/Dark_Matter), whatever the heck the "dark energy (http://en.wikipedia.org/wiki/Dark_Energy)" is, and ???) and how the energy densities of these constituents change with time (or equivalently, with the scale factor R) will dictate the how the universe will evolve over the distance scales in which these constituents are approximately homogeneous.

The standard model deals only with space-time already in a state of expansion. What set the universe "in motion"? A quantum mechanically based model construct, known as "Inflation (http://en.wikipedia.org/wiki/Inflationary_cosmology)" (more appropriate links for beginners, here (http://www.lifesci.sussex.ac.uk/home/John_Gribbin/cosmo.htm) and here (http://map.gsfc.nasa.gov/universe/bb_cosmo_infl.html)), attempts to address several issues not addressed by the standard model. About 2 billion J (roughly, the energy in a half a tank of gasoline) is the energy equivalent to the Planck mass (http://en.wikipedia.org/wiki/Planck_energy), which is the energy allowed over a Planck time (http://en.wikipedia.org/wiki/Planck_time) interval via the Heisenberg Uncertainty Principle (http://en.wikipedia.org/wiki/Uncertainty_principle). A scalar potential field, known as the Inflaton field, undergoing quantum fluctuations was caught up momentarily in a false vacuum (http://en.wikipedia.org/wiki/False_vacuum) (excited) energy state, with that ~2 billion J. This was apparently all that was needed to create conditions for a rapid, exponential expansion of space-time, the so-called inflationary epoch (http://en.wikipedia.org/wiki/Inflationary_epoch).

This particular equation of state (http://en.wikipedia.org/wiki/Equation_of_state_(cosmology)) (space filled with energy of the quantum vacuum) has negative pressure, meaning the fluid (here, the quantum vacuum (http://en.wikipedia.org/wiki/Quantum_Vacuum)) behaves energetically as if under tension. Expand a normal gas and it loses energy. Stretch a rubber band or spring (or create a larger surface under tension) and the energy increases with size. The negative pressure characteristic of this fluid drives an exponential expansion (i.e., repulsive gravity), whereby the energy density (energy per unit volume) remained constant (http://en.wikipedia.org/wiki/Cosmological_constant) as space-time expanded. In other words the energy content of the vacuum grew in step with the exponential expansion. After ~10^{-32} s, the potential field decayed in energy, resulting in the creation of relativistic quantum particles (photons and other particles which eventually became quark/anti-quark pairs (http://en.wikipedia.org/wiki/Virtual_particles#Pair_production)) out of the energy now contained within space.

A recent, and much less developed model, Loop Quantum Gravity (http://en.wikipedia.org/wiki/Loop_quantum_gravity) tries to account for the conditions which led to the inflationary epoch.
(http://en.wikipedia.org/wiki/Inflation_%28cosmology%29#Inflation_and_loop_quant um_gravity)
In some respects this whole process is similar to the phase transition (and symmetry breaking) properties of the condensation of water vapor (symmetric; high energy state) into an ice crystal (less symmetric; low energy state), and indeed the model posits that symmetry breaking resulted in the 3 gauge forces (http://en.wikipedia.org/wiki/Gauge_theory) (electromagnetism, weak and strong nuclear forces).

When all was said and done there was expanding space-time filled with a relativistic matter-photon fluid, evolving over time: cooling, becoming more dilute. The expansion of space-time has been "coasting" ever since (like a ball thrown straight up, decelerating during the climb up), but this expansion evolving in time depending mainly on the dominant constituent at that time. As the energy density of the universe dropped over time, relativistic particles gave way to non-relativistic matter (apparently dominated by dark matter), which has recently (beginning about ~7 Gyrs ago) given way to dark energy --- and each has left its thumbprint on expanding universe for us to discover. This last has apparently taken hold of the universe as the matter and photon energy densities have declined precipitously, and to our utter amazement the "tossed ball" mentioned above is undergoing positive acceleration.

In short, about 2 billion Joules. :whistle:

PraedSt
2008-Nov-27, 07:23 AM
That's a great overview Spaceman Spiff. Thanks. :)

sethoscope
2008-Nov-27, 10:32 AM
Thanks Spaceman!!!

I'll need some time to digest the information that you've provided but as I do I'll post any related questions right here. Thanks for taking the time to address my question.

Sethoscope

Spaceman Spiff
2008-Nov-27, 01:39 PM
You're both very welcome.

As much as there was to digest (and I hope it wasn't too much; my apologies for the length), it's only the tip of the iceberg in terms of the depth of physical understanding. That some sort of inflationary phase, involving fluctuations in the quantum vacuum, took place is consistent with several lines of independent evidence (http://map.gsfc.nasa.gov/universe/bb_cosmo_infl.html), but it is by no means an established scientific fact. The nature of space-time (and of a potentially much larger landscape (http://en.wikipedia.org/wiki/Multiverse) thereof (http://en.wikipedia.org/wiki/Chaotic_inflation)) "before" this phase is at the present time far more speculative, although there are legitimate scientific models attempting to address this. Of course, these are fertile pursuits from the scientific point of view only to the extent that they have left observable consequences in our universe.

mugaliens
2008-Nov-28, 10:35 AM
So there really was no big explosion and thus the term Big Bang is a bit misleading. However movement usually requires energy in some form or another (ect. kinetic, potential, thermal, gravitational, sound . . . )

Yes - movement does. But expansion is not movement. And the term "acceleration" when applied to expansion doesn't involve an applied force, but rather, it's merely an increase in the rate of expansion.


I guess I was asking is there any theories or ideas about what is fueling the expansion including the initial rapid inflation, the linear expansion and the recent acceleration? Perhaps this gets into muliverse theories.

I believe Cougar covered that quite nicely (http://www.bautforum.com/questions-answers/81649-expanding-universe-energy-question.html#post1373297). It appears virtual particle creation is responsible for expansion, and as he stated, they cancel one another out 99.999999999...% of the time. Just not 100% of the time, which is where we get addition energy, matter, and spacetime itself.

This isn't a new concept. Heinlein himself touched on it in his 1986 novel, "The Number of the Beast," where the gang translated into a new universe totally void of any detectible matter or EM. Before the translated out of it, they postulated it was a null universe, and that by translating in, they created the universe itself, their matter and EM energy giving it form, it's very existence.

Is it a stretch to assume that the not quite total annihilation of virtual particle pairs is what's causing expansion? That the introduction of matter itself is which continues to give the universe more form?

Who knows - one day it may be decided that we're nothing more than a leak in physics.

sethoscope
2008-Nov-28, 04:19 PM
Thanks Mugs!

I'm still digesting the info on "inflation" and "expansion".

It's going to take me awhile but I appreciate your clarification on movement and expansion. Here's a quick question.

Couldn't expansion be a form of potential energy? Like a spring?

I need to research the annihilation of virtual particles more. I read a book awhile back about this but I've forgotten most of it. If I remember right this is the annihilation of particle and anti-particle??? Or perhaps I'm mixing everything up.

This journey won't be over anytime soon . . . but the ride is great!

mugaliens
2008-Nov-28, 09:25 PM
Thanks Mugs!

I'm still digesting the info on "inflation" and "expansion".

It's going to take me awhile but I appreciate your clarification on movement and expansion. Here's a quick question.

Couldn't expansion be a form of potential energy? Like a spring?

Possibly, but if the theory holds, probably not, as that theory holds that the very fabric of spacetime, and expansion itself, is created/formed by the introduction of particles within it. The only way to get it to "spring back" would be to remove a substantial amount of the energy-matter within it.


I need to research the annihilation of virtual particles more. I read a book awhile back about this but I've forgotten most of it. If I remember right this is the annihilation of particle and anti-particle??? Or perhaps I'm mixing everything up.

This journey won't be over anytime soon . . . but the ride is great!

Well, again, don't rush off. This is but one theory of which I'm aware, and I'm even sure if it's the leading one or not.

Any other comments? Ken G? Ilya?

sethoscope
2008-Dec-01, 06:30 AM
Ok I'm working my way through all the wonderful material and references provided above and I want to make sure that I understand the uncertainty principle. Here's a quote from Wikipedia:

"In quantum physics, the Heisenberg uncertainty principle states that the values of certain pairs of conjugate variables (position and momentum, for instance) cannot both be known with arbitrary precision. That is, the more precisely one variable is known, the less precisely the other is known. This is not a statement about the limitations of a researcher's ability to measure particular quantities of a system, but rather about the nature of the system itself."

Now to apply this principle to something a bit easier to visualize; could we use the example of a radar gun by the highway patrol to catch a motorist going over the speed limit? If it can be applied then we could argue that while yes the police officer could detect our speed with great accuracy, he could never prove our exact location when the speed was measured?

This could really prove useful next time I get pulled over!

And going back to particle physics, how does this apply to our understanding of the Universe and this Wikipedia quote?

"The uncertainty principle requires that when the position of an atom is measured, the measurement process will leave the momentum of the atom changed by an uncertain amount inversely proportional to the accuracy of the measurement. The amount of uncertainty can never be reduced below the limit, no matter what the measurement process."

mugaliens
2008-Dec-01, 05:56 PM
This could really prove useful next time I get pulled over!

If the radar gun only used one photon, then yes, you could make that arguement. Sadly, they use trillions.

Cougar
2008-Dec-02, 02:59 AM
These solutions (http://en.wikipedia.org/wiki/Friedmann_equations) are nothing more than equations of motion for this fluid of matter-energy as a function of time....

About 2 billion J (roughly, the energy in a half a tank of gasoline) is the energy equivalent to the Planck mass (http://en.wikipedia.org/wiki/Planck_energy), which is the energy allowed over a Planck time interval (http://en.wikipedia.org/wiki/Planck_time) via the Heisenberg Uncertainty Principle (http://en.wikipedia.org/wiki/Uncertainty_principle).


Yes, tremendously informative and concise post, Professor!

Spaceman Spiff
2008-Dec-02, 03:43 PM
Glad to have been of some assistance.:)