Faster than light is normal

[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.scienceforums.net/forums/showthread.php?p=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]

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.ucla.edu/~wright/cosmolog.htm

 

http://www.astro.ucla.edu/~wright/cosmology_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.caltech.edu/level5/March03/Lineweaver/Lineweaver_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]

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

 

besides which' date=' since space has expanded by a factor of 1100

a sample volume has expanded by a factor of (1100)[sup']3[/sup]

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"!

 

 

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' date=' 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---[/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)

[Sayonara]

our eleven dimensions cancel out the tachyon frequencies.

Evidence? Or at the very least, reasoning?

 

 

tachyons dont exist.

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

 

 

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]

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...

[Sayonara]

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?

[TheProphet]

Most of the math needed for String/M thoery haven't and even haven't been able to count(worked out.. hey im swedish ).. And also.. one even simpler thing is that String thoery gets more an more complex as it goes. Souns like they are trying too patch the theory togehter more and more with even more complexity.. and you should keep it as simple as possible (Which also Einstein said) Lots of other theorys seem to have equel or even bether chance to quantize Gravity..

Im not saying M/string thory is wrong.. no theory never really are! Still interesting but seem to get too complex to be true... but who knows. Altough u seem to have worked your faith out! Good for you

[JaKiri]

what is wrong with string theory?

 

At the moment, it's about the same distance from a nobel prize in physics as 'Wouldn't it be nice if we could all get along' is from a nobel prize in peace.

 

In the end reckoning, string theory hasn't predicted anything yet, and hasn't actually done anything yet. If it all (ever) gets worked out, it could be wonderful, but currently to base assumptions or predictions on it is foolish at best.

[ydoaPs]

it WOULD have predicted the masses and acharges of elementary particles, but we already knew them. the properties found by string theory were correct

[JaKiri]

it WOULD have predicted the masses and acharges of elementary particles, but we already knew them. the properties found by string theory were correct

 

That's a circular argument at best.

[ydoaPs]

what I meant was, if we had no knowledge of the properties of particles, then string teory would have predicted them