If the Universe is Expanding...

Originally posted by CLPrime
Nope, no paradox. Read this post of mine... the first half of it. The universe is free to expand as fast as it wants without violating any speed limits.

So how then do you differentiate between relative motion caused by an expanding space time and proper motion?

reply to post by Clavicula


It's not relative motion, it's apparent motion (relative motion is still subject to Relativity). But, that's semantics. And, of course, galaxies do have some level of motion relative to the Earth, so, as you say, we have to differentiate between the proper motion of stars/galaxies and their apparent motion caused by the expansion of the universe. Here's the deal...

Apparent and proper/relative motion is found by measuring how much the light has been redshifted:

Doppler redshift is caused by an object physically moving away from us (if the object is moving towards us, this produces a blueshift).
Cosmological redshift is caused by the light being stretched out as space expands.

They are differentiated by measuring the rate of change in the object's redshift with respect to the "standard" set by the Cosmic Microwave Background. Anything beyond that standard is Doppler.

reply to post by CLPrime


I was referring to the analogy of the inflating balloon where dots on the balloon representing galaxies and the expansion of the balloon representing the expansion of the universe. In all explanations i have seen the "2 dimensional" skin of the balloon is meant to represent 3 dimensional space and the spherical shape of the balloon then being 4th dimensional.

Your explanation seem to imply that the expansion is a 3 dimensional expansion only.

Originally posted by KrzYma
I don't believe "them", is the Universe expanding or not.
I don't believe Einstein or others who push and stretch a theory to keep it alive.
I don't believe Light Speed is constant course it changes with mass.
I don't believe in Black Matter or Black Energy or whatever they need to keep RT alive

time for corrections!

reply to post by Clavicula


I know you were. The balloon model is a helpful illustration of expansion (I used it, myself, in this thread), but it's inaccurate, overall. It represents a "closed" universe, when, according to our observations, the universe is flat. A better illustration would be if you cut a circle out of the balloon's rubber and stretched it out on the surface of a table - with the rubber still representing our 3-dimensional space.

Originally posted by CLPrime
reply to post by Clavicula

 

It's not relative motion, it's apparent motion (relative motion is still subject to Relativity). But, that's semantics. And, of course, galaxies do have some level of motion relative to the Earth, so, as you say, we have to differentiate between the proper motion of stars/galaxies and their apparent motion caused by the expansion of the universe. Here's the deal...

Apparent and proper/relative motion is found by measuring how much the light has been redshifted:

Doppler redshift is caused by an object physically moving away from us (if the object is moving towards us, this produces a blueshift).
Cosmological redshift is caused by the light being stretched out as space expands.

They are differentiated by measuring the rate of change in the object's redshift with respect to the "standard" set by the Cosmic Microwave Background. Anything beyond that standard is Doppler.

edit on 22-5-2011 by CLPrime because: (no reason given)

As you say this is semantics, By relative motion I refer to the fact that the measured distance between objects increase. This would happen regardless whether the space time expands or if the object moves relative to their respective spatial position. And the redshift would be the same as well and would not reveal the mode by which difference in relative distance is accomplished. But this is of cause all, as they say, academic. We can agree on the fact that the universe has during the cause of its development expanded (again using my definition of relative motion) faster than the speed of light. You claim that this is not breaking with established laws of physics, since the mode of change matter and that the objects are at rest in their respective reference frame.

I will have to give that particular argument some more thought.

reply to post by CLPrime


Fair enough, but that does not exlude the 4D aspect of universal expansion even if there is no way to tell as the direction of expansion does not have an apparent 4D spatial component.

imagine a rubber band with solid balls in evenly spaced intervals along the surface....

now pull the band at both ends .. the spaces between the balls will get bigger , but the balls will stay the same size.

this is because space itself is expanding not all matter in space.

How do you differentiate between space and the "space" it's supposedly expanding into?

double post

reply to post by FOXMULDER147


Space isn't "supposedly" expanding into anything. If we consider the Big Bang to be the creation of space and time, then space and time don't exist beyond the "edge" of the universe it created. But, then, from our vantage point, I don't really see how we can make such a determination.

reply to post by smithjustinb

What does it mean to say that the Universe is expanding? If EVERY thing in the universe is expanding, or getting bigger, then that means we're all getting bigger. We wouldn't notice that we were getting bigger because everything around us is also getting bigger and at the same rate. Know what I mean? It's crazy to think about.

Think of the raisen bread metaphor! The raisens stay about the same size. The dough expands. Mmm yummy raisen bread..

reply to post by smithjustinb


What if electromagnetic propagation loses energy over large distances. If the light has a natural loss of energy that leads to a move in wavelength a.k.a. red shift.

Such a red shift would be indistinguishable from red shift caused by the doppler effect. The red shift that occur with distance could then be a misinterpretation of a completely different effect that lead to a false conclusion.

reply to post by Clavicula


Such "tired light" models have indeed been proposed. But there are certain problems with such explanations compared to metric expansion model:
en.wikipedia.org...

Originally posted by Maslo
reply to post by Clavicula

 

Such "tired light" models have indeed been proposed. But there are certain problems with such explanations compared to metric expansion model:
en.wikipedia.org...

edit on 23/5/11 by Maslo because: (no reason given)

The critisisms are not completely detrimental to the idea. Obviously it is not a scattering that takes place but could be a not yet discovered property of electromagnetic radiation over vast distances. I guess the problem would be to set up an experiment that can be performed on human time scales and distances.

Originally posted by Clavicula

The critisisms are not completely detrimental to the idea.

In fact, they are. There is no physically possible version of the "tired light" hypothesis. Here's the most conclusive reason why:

Consider the Cosmic Microwave Background (CMB). According to the current model (and current observations), the CMB is blackbody radiation emitted ~13.7 billion years ago. To emit blackbody radiation, a region must be absorb light evenly throughout (which, in astrophysics, is called "opaque"). In the current theory, this condition was met by the early universe, so, at that time, it was emitting blackbody radiation. When the universe then became transparent, as it expanded and cooled, the last of the blackbody radiation was allowed to travel freely, and this is what we are seeing now in the CMB.

However, let's assume a static universe (where there is no cosmological redshift - so, the overwhelming majority of redshifting is attributed to "tired light"). This requires that the blackbody radiation of the CMB be coming from some region of the universe as we see it today. The problem is, our local area of the universe is transparent, so it cannot emit blacbody radiation. However, some will say that it's a far-away region of the universe that the blackbody radiation is coming from. Well, let's find out how far away it would have to be...

The temperature of the CMB, which we can measure directly, is 2.725 K. In a static universe, space is not expanding, so the density of the blackbody radiation is constant, and, therefore, its temperature decreases only as a result of the redshifting.
Now, the spectrum represented by any blackbody radiation must show a very specific distribution (it peaks at a certain wavelength and falls off on either side). Given this, we can find at what redshift/distance an object must be to produce the observed spectrum (and how much it deviates from a pure blackbody spectrum). Sparing you the math, to obtain a temperature that deviates from the blackbody spectrum even at the limit of our observational error (which shows the CMB is a pure blackbody spectrum within a prefactor of 1.00001 +/- 0.00005), the maximum distance the source of the CMB must be at is 815,000 light-years. This 1/3 the distance to the Andromeda Galaxy. Obviously, the universe is transparent well beyond this point.

The source of the CMB cannot be an opaque region of our contemporary universe. This eliminates the tired light theory, which requires a contemporary source for the CMB.

Originally posted by CLPrime
reply to post by FOXMULDER147

 

Space isn't "supposedly" expanding into anything. If we consider the Big Bang to be the creation of space and time, then space and time don't exist beyond the "edge" of the universe it created.

I don't consider the Big Bang to be the creation of space.

The Big Bang had to happen in space. A pre-existing space.

this whole Big Bang and Expanding Universe is just a Theory, point!!!

There is no solid evidence of it and that's why they try to back up this theory at all costs.
Problem on this is, if the conclusion on some observation comes from wrong theory... well, all looks right but it doesn't mean IT IS!
Then they need to create even more spooky thing throwing even more questions to correct they maths
( truly money making machine , pay for one questions and get another two created )

Few century's ago Greece scientists observed the planets in solar systems, they thought Earth is in the canter, so they could not explain the funny orbiting paths of the planets they have observed. The planets were moving for and backwards... well, they described es es good es they could at this time and it stands for hundreds of Years as proven fact... like expanding universe is now the theory till someone proves them other wise!

in fact, new theory tells us, Big Bang and its Horizont Problem can be explained with Variable Speed Of Light what seems plausible if you think of it for the first time.

as I said, one problem looks solved, but you get two new instead

Originally posted by FOXMULDER147

Originally posted by CLPrime
reply to post by FOXMULDER147

 

Space isn't "supposedly" expanding into anything. If we consider the Big Bang to be the creation of space and time, then space and time don't exist beyond the "edge" of the universe it created.

I don't consider the Big Bang to be the creation of space.

The Big Bang had to happen in space. A pre-existing space.

Why?