[Martin]

most of the galaxies that we will ever be able to see with our telescopes are receding from us at FTL speeds

and indeed were recedingfrom us FTL when they emitted the light that we are now receiving from them

and Einstein's theory of special relativity does not contradict this
because it has nothing to say about recession speeds (the rates at which distances are increasing) but only about speeds of local encounter

but some people dont realize this and assume that the galaxies we are looking at cannot be receding from us FTL

and they may also think the redshift is a doppler effect
which you learn already in basic introductory astronomy courses it is not
(a careful distinction is made between cosmological redshift and doppler shift)

also think about this: the universe is full of CMB photons
which have experienced a redshift of 1100
that is, each photon has lost 1100/1101 of its energy---it has lost over 99 percent of its original energy from the 'recombination' era when those photons originated

where has this huge amount of energy gone? is there a global energy conservation rule in Gen Rel that says it has to have gone somewhere?

probably several people at SFN are equipped to discuss this, fafalone's profile says he's interested in cosmology and my guess is a bunch more are too and these are basic cosmology topics

[Martin]

As for most recession speeds being FTL
put redshift z = 2 into the calculator here
http://www.sciencefo...56565#post56565

to set things up you first need to put 0.27 for matter and 0.73 for dark energy and 71 for the hubble parameter, which are standard cosmology estimates.

galaxies as distant as z =10 have been observed, so
way more are out there with z > 2
than are with z < 2

that is why it is typical or normal for a galaxy in the observable part of the universe to have redshift z > 2
so accordingly it is normal for them to be receding FTL

[TheProphet]

Lost energy? As far as i know light can't lose it's energy! Altough in this situation it will lose it's intensity! But not it's energy level. Or well the CMB:s total energy level raminas the same! But CMB level per Space is lower due to the strectching of space! So then the energy hasn't been lost, just streched as well...

[Martin]

TheProphet said:

Lost energy? As far as i know light can't lose it's energy! Altough in this situation it will lose it's intensity! But not it's energy level. Or will the CMB's total energy level remain the same! But CMB level per Space is lower due to the strectching of space! So then the energy hasn't been lost, just streched as well...

I will try to direct you to a standard cosmology FAQ
maybe Ned Wright's cosmology tutorial FAQ will work for you

http://www.astro.ucl...ht/cosmolog.htm

http://www.astro.ucl...mology_faq.html

he teaches the undergrad and graduate level courses in cosmology at UCLA
and is also one of the team in charge of the WMAP satellite observing the CMB

You are mistaken. Light can lose its energy. there is no global energy conservation law in General Relativity.

the expansion of space has two effects:
one (which you pointed out) is that there are fewer photons per cubic kilometer-----they get spread out into a larger volume

the other is that an individual photon loses energy as its wavelength gets stretched out

the energy of a CMB photon is hc/lambda where h is Planck constant and lambda is the wavelength-----stretching out the wavelength reduces the photon's energy

roughly speaking: each CMB photon has individually lost 1100/1101 of its energy since the time when they were all last scattered

besides which, since space has expanded by a factor of 1100
a sample volume has expanded by a factor of (1100)³
so CMB energy-per-volume has declined by a factor of
(1100)⁴

this fourth power relation is a standard fact you get taught in an introductory cosmology course or will find referred to in
pedagogical articles

it is surprising

the density of matter only goes down as the cube
but the energy density of radiation falls off as the fourth power

Try this article by Lineweaver (he was one of the team in charge of COBE
an earlier CMB satellite observatory)

Inflation and the Cosmic Microwave Background
http://nedwww.ipac.c...r_contents.html

http://arxiv.org/astro-ph/0305179

the second link has a PDF version that is more readable but takes more time to download

this essay of Lineweaver has been made into a chapter of a new book now in press called "The New Cosmology" (world scientific 2004)

here's the part of my post I believe you were responding to:
---quote---
also think about this: the universe is full of CMB photons
which have experienced a redshift of 1100
that is, each photon has lost 1100/1101 of its energy---it has lost over 99 percent of its original energy from the 'recombination' era when those photons originated

where has this huge amount of energy gone? is there a global energy conservation rule in Gen Rel that says it has to have gone somewhere?
---end quote---

[TheProphet]

Martin: I'll take my time tomorow and read upp on that.. Sounds really interesting, since i didn't tought it was possible. This opens also upp new scenarios, in my mind =)

Thanks for the links =)

[TheProphet]

Quote

roughly speaking: each CMB photon has individually lost 1100/1101 of its energy since the time when they were all last scattered

besides which, since space has expanded by a factor of 1100
a sample volume has expanded by a factor of (1100)³
so CMB energy-per-volume has declined by a factor of
(1100)⁴

this fourth power relation is a standard fact you get taught in an introductory cosmology course or will find referred to in
pedagogical articles

it is surprising

the density of matter only goes down as the cube
but the energy density of radiation falls off as the fourth power

Well this is very interesting! To me it almost lokes like if Radiation is downsizing in 4 dims and matter in 3... Which again mess mu head upp.. This really calls for the "thinker hat"!

Quote

here's the part of my post I believe you were responding to:
---quote---
also think about this: the universe is full of CMB photons
which have experienced a redshift of 1100
that is, each photon has lost 1100/1101 of its energy---it has lost over 99 percent of its original energy from the 'recombination' era when those photons originated

where has this huge amount of energy gone? is there a global energy conservation rule in Gen Rel that says it has to have gone somewhere?
---end quote---

Even more interesting, also since my belif where contradicted. Something somehere must have taken upp the energy (logicly). Well guess we need to disect GR.. then..

[ydoaPs]

our eleven dimensions cancel out the tachyon frequencies. tachyons dont exist. nothing can go faster than the speed of light (light in a vacum)

[Sayonara³]

yourdadonapogos said:

our eleven dimensions cancel out the tachyon frequencies.

Evidence? Or at the very least, reasoning?

Quote

tachyons dont exist.

Santa position. Lack of evidence for is not evidence against.

Quote

nothing can go faster than the speed of light (light in a vacum)

Except tachyons, which don't have a positive or zero rest mass.

[ydoaPs]

it is math. the eleven dimesnsions cancel out the tachyon frequencies, therefore they do not exist

[ydoaPs]

IF tachyons existed, they would have imaginary mass. how can something have imaginary mass?

[Cap'n Refsmmat]

yourdadonapogos said:

it is math. the eleven dimesnsions cancel out the tachyon frequencies, therefore they do not exist

And how is that?

Can you be sure there are eleven dimensions?

[TheProphet]

Imaginary Mass is just as real as 11 Dimensions and your evidences.... for the moment... FTL recesions speed is Space movin.. not any particle.. so it's highly possible, and also hace evidence form measurments...

[ydoaPs]

how can imaginary mass be real? it is like negative distance (point A is closer to point B than point B is to itself)

[TheProphet]

How can 11 dimensions be.. At the moment we know jsut as little about both.. gues we know more of imaginary math though...

[Sayonara³]

yourdadonapogos said:

how can imaginary mass be real? it is like negative distance (point A is closer to point B than point B is to itself)

Not the best example, as distance relies on available routes.

[ydoaPs]

oops i accidently made a pun, sorry "how can imaginary mass be real" lol

[ydoaPs]

for the eleven dimensions we invoke the mighty powers of calibi-yau manifolds

[TheProphet]

Well Calabi-yau:s look very nice on papper.. but there are more theories! And as far as i'm concerned String theory have huge troubles, when other fields make big stepes forward... Ad don't forget that it's M theory that gives u 11 dimensions.

[ydoaPs]

string theory is part of m-theory. m-theory combines all string theories into one

[ydoaPs]

what is wrong with string theory?