Question about redshift etc.

[blike]

A creationist friend of mine is claiming that the reason we see distant starlight is because there was a rapid expansion of the universe at creation. The universe expanded for about 2 picoseconds to its present size, and lightwaves along with everything else were stretched. This, he says, explains the redshift of distant galaxies. The farther the galaxy, the more expansion had to have occured, the more redshift (stretched light) we see.

 

Is there a way to test this idea? I'd imagine there's got to be a way to measure the spectral emissions of distant elements, note the redshift, and calculate what kind of expansion could have created this redshift and see if it correlates with the star's known distance. Anyone?

[Martin]

...and lightwaves along with everything else were stretched. This, he says, explains the redshift of distant galaxies. The farther the galaxy, the more expansion had to have occured, the more redshift (stretched light) we see.

 

Is there a way to test this idea? I'd imagine there's got to be a way to measure the spectral emissions of distant elements, note the redshift, and calculate what kind of expansion could have created this redshift and see if it correlates with the star's known distance. Anyone?

 

there is a lot of accepted mainstream, in what your friend says.

we can try to sift it out.

yes there is a way to test the idea that lightwaves behave as if stretched by the expansion of space

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Various things to do this morning and time fragmented, so can only nibble away gradually.

 

Remember that cosmologists cannot declare their consensus mainstream cosmology picture to be "true". A scientific model can only be repeatedly tested and checked----and one can say it has not been disproved YET but not that it is true.

 

However there is currently a successful mainstream cosmology model that has been tested and checked a lot of ways and is provisionally accepted.

 

That model is based on the the FRW metric which is a simplified solution to the Einstein eqn. of Gen Rel.

A particular form of that model is called "Lambda-CDM" for lambda cold dark matter. It is the prevailing one in use by working cosmologists.

 

In that model, and similar ones, distances between things increase according to an increasing function of time called the scale factor, a(t) or R(t), and in effect lightwaves DO GET STRETCHED OUT (!) and this is the cause of the observed cosmological redshift.

 

This is a really curious thing. The cosmological redshift observed in the light of distant galaxies is not a Doppler effect! It is not caused by the galaxy moving away at the time it emitted the light. It is caused by the stretching of space that occurred all during the time the light was on its way to us.

 

A small percentage of a galaxy's observed redshift can be a Doppler shift caused by some random motion the galaxy had at the time it emitted the light, or to our motion as we receive the light. These effects can be large with nearby galaxies where there has not been much expansion of space while the light was traveling. But these Doppler shifts are mostly negligible compared to the stretching, which is the main deal.

 

[This expansion is not confined to the first fraction of a second. Your friend sounds like he is confusing several things and getting a more speculative thing mixed in which is the INFLATION scenario. Cosmologists have not reached consensus about whether Inflation (very rapid expansion) occurred in the first fraction of a second (there are alternative proposals which make it unnecessary to assume inflation) and they have not settled on one particular mechanism that might have caused inflation. So there are a number of Inflation Scenarios. they call them scenarios instead of theory or hypothesis because they are still kind of iffy. Maybe some Inflation scenario will be tested and will come to be generally accepted----I personally suspect that it will BTW----but the thing to notice is that this is a side issue: Expansion stretching out lightwaves is not just a first fraction of second deal, it has been going on for 13 billion years and is still going on.]

 

I've got a bunch of things to take care of. Maybe someone else would like to take over. There are several interesting issues here and we could certainly use more discussion to get things sorted out.

 

 

footnote: "space expanding" simply means distances between stationary objects increase

and this doesn't need to cause yardsticks or galaxies to expand because they are held together by their own internal forces

like the bonds between atoms in a crystal, or the gravitational bonds holding planets in orbit.

but a lightwave is not like a material object such as a yardstick, that is held together by internal forces----it is basically a geometrical thing so when distance expands (as it does very very slowly) the lightwaved is stretched. imagine solving Maxwell's equations in a space where distances expand by a tiny tiny percentage every second.

[blike]

there is a lot of accepted mainstream, in what your friend says.

As I understand it, inflationary theory makes a similar statement about the initial picosecond of inflation. I'm more interested in exploring the characteristics of redshift because of coordinate expansion versus the characteristics of redshift because of recession.

 

Imagine the sun and the earth suddenly moving away from each other because of coordinate expansion so that in just a few picoseconds they are hundreds of thousands of light years apart. What would the redshift of the sun's like be? Is there a way to calculate the impact on the wavelength of the hydrogen emissions?

 

Now imagine the sun and the earth are receding more slowly but over the course of a billion years. Eventually we are a hundreds of thousand light years apart.

 

Is there a way to delineate which type of expansion occurred (slow expansion for a long time, or rapid expansion for an extremely short time) based on the redshift?

[J.C.MacSwell]

A creationist friend of mine is claiming that the reason we see distant starlight is because there was a rapid expansion of the universe at creation. The universe expanded for about 2 picoseconds to its present size, and lightwaves along with everything else were stretched. This, he says, explains the redshift of distant galaxies. The farther the galaxy, the more expansion had to have occured, the more redshift (stretched light) we see.

 

Is there a way to test this idea? I'd imagine there's got to be a way to measure the spectral emissions of distant elements, note the redshift, and calculate what kind of expansion could have created this redshift and see if it correlates with the star's known distance. Anyone?

 

Wouldn't they all be stretched the same amount but, due to the extra distance of anything more than X lightyears away (X being the time since creation), the light from those sources simply would not have arrived yet?

[Cap'n Refsmmat]

We've been able to tell what the inflation rate was at various times throughout history (with good accuracy) by comparing the redshifting of supernovas at various distances. Find that data and show it to him.

[Martin]

thanks for commenting MacSwell, it helps to see how other people react.

 

Blike, I am beginning to understand your question better now i think.

Your friend has elements of normal science in his story, like inflation and expansion increasing wavelengths. This is to his credit. But what you are asking is whether his overall creation account is plausible or not and how could it be disproved empirically.

 

I think he is driving at a RECENT creation in which all observable galaxies used to be close together and then in the twinkling of an eye they are all expanded out to their present distances.

 

this would be observationally distinguishable from a slow dispersion because in the quick case the light coming in would be so feeble we couldnt see it. Only X many photons would be on their way from A to B when they are close----and then expand instantly and there are still just those X photons on their way----the wavelength would be stretched out as we observe, but the POWER would be absurdly less than what we observe. here are some more points, if you want to try arguing with your friend:

 

1. During expansion galaxies stay the same size. (he may not know this.) So his story is implausible because it is hard to imagine billions of galaxies crowded together in the original staging area without their disrupting each other.

 

2. In reality, we observe galaxies at different stages of their life. Very far away we see very young galaxies condensing with early star-formation regions. the early stars have less heavy elements in them, they burn down rapidly and explode so that later generations of stars can have more "metals", i.e. more elements heavier than helium. Both stars and galaxies have a natural life cycle. Later generation stars have more metals. Elliptical galaxies form from the collision and merger of spirals etc.

 

Your friend's picture does not provide for seeing galaxies at earlier and earlier stages of life as you go farther away. His picture has everything inflated instantly.

 

Also his initial staging area has to contain galaxies which LOOK LIKE the ones we now see. Because he is going to instantly spread them out and their images are going to be coming to us looking just as they looked in the staging area.

 

But that is not realistic because since galaxies stay the same size during the expansion of space there would be all these huge things crammed in together and they would be disrupting each other and they would not look like usual galaxies----it would probably be a very hot dense soup, like of quarks and stuff. So when you suddenly dispersed it, it wouldnt look like familiar galaxies.

 

Anyway these are some arguments you can try with him.