accelerating expansion of the universe doesn't fit

[Chiropteran]

Supernovae are star explosions ... With a decent idea of the explosion's absolute and apparent brightness, astronomers can determine the distance to these objects. Then, knowing the redshift, they can calculate how fast the supernovae are moving away from us. Turns out that the most distant Type 1a supernovae are moving away much faster then closer ones, suggesting that the universe's expansion is actually accelerating, not decelerating.

Read that last line again.

"the most distant Type 1a supernovae are moving away much faster then closer ones, suggesting that the universe's expansion is actually accelerating, not decelerating."

It doesn't follow.

Do you see the problem I see?

Distant supernovae(sic) are detected to be moving faster than closer supernovae, okay, I got that.

That implies that the rate of expansion is accelerating? I don't agree.


The distant supernovae are being detected now for the first time, but they actually occurred a long freaking time ago. 1 year ago per light year away.

While the closer supernovae occured more recently.

The more recent supernovae are moving away slower than the old ones.

So, they were moving away fast a long time ago, but in the more recent past they are moving away slower. I see that as showing a reduction in the expansion of the universe, not an acceleration.

What am I missing?

 

[sjwaste]

This is one of those times where a balloon analogy works.

Take a balloon, blow it up half way. Get 3 pieces of tape and put them in a line, spaced equally, and somewhat apart. One on the end is you. The second is a close 1a, the 3rd is a distant 1a. Now inflate the balloon so that the first piece of tape is twice as far from you as it was before. What happens?

Do it again, watch it expand. The distances increase depending on how far away from you the piece of tape, or supernova, was as you inflate it. This is pretty much what happens as spacetime itself expands.

I think this illustration works. If not, someone smarter than me will tell me to get the hell out

EDIT: I don't think I summed it up at all. As spacetime expansion accelerates, every point (using the term loosely) between any two objects expands. Therefore, an object positioned relatively distant from you will move farther away faster than one relatively closer to you, because of the expansion of spacetime in between. I think I had to use the balloon analogy to understand it.

 

[Chiropteran]

The balloon analogy describes the motion of an expanding universe. I understand that. What I don't understand: where do they get the evidence that the universe is expanding?

See, you are putting the theory before the experimental data that proves the theory. It doesn't work like that, you need to have the data first to build the theory. The expanding balloon analogy is based on the assumption that galaxies further away from us are moving away from us faster. The problem I have is that how do we know they are moving away from us faster? All we know is that they were moving away from us faster when the light we now see was emitted.

For example, a galaxy "A" is 5 billion light years away and appears moving away from us faster than a galaxy "B" which is 2 billion light years away.

BUT, the light we see from galaxy "A" was actually emitted 5 billion years ago! I don't see how we can make any assumption about it's current acceleration based on how it was moving 5 billion years ago. What if it was just moving faster 5 billion years ago because it was still carrying momentum from the big bang, and has since slowed down? I don't see how we could know.

As I said above, a supernova far far away from us is *also* a supernova that occurred a long long time ago. With the information I have seen, it seems like the scientists just assume that the supernova is moving away from us faster because of the distance, while they ignore the possibility that it is moving away from us faster because it occurred a really long time ago and maybe things were moving faster back then.

Basically, I see it as a flawed experiment because there are two different variables- distance and time. How can they know the acceleration is due to distance but not time? I think it's impossible to tell. If all the galaxies were originally moving apart at some incredible speed, but they have been slowing down since the big bang, it would make perfect sense for us to perceive the furthest galaxies as moving faster, because we are seeing the light from them that occurred long ago before they had time to slow down.

 

[sjwaste]

Originally posted by: Chiropteran
See, you are putting the theory before the experimental data that proves the theory. It doesn't work like that, you need to have the data first to build the theory. The expanding balloon analogy is based on the assumption that galaxies further away from us are moving away from us faster. The problem I have is that how do we know they are moving away from us faster? All we know is that they were moving away from us faster when the light we now see was emitted.

I see what you're saying, and have no idea. I mean, we can't observe them instantaneously, so all we can really say is that the light reaching us now from the more distant galaxies is moving away from us faster than the light reaching us from those closer. I'm really not sure if the current theory just assumes that they continue at that velocity or if there's other data that can be interpreted to mean that they are, in fact, doing so.

Really interesting thought, now that I understand what you were asking better.

I guess what the data tells us is that those distant galaxies were moving away from us faster than galaxies closer to us were moving away from us when their light reached us. Unless there's something we don't know about to slow them down, we assume it continues? Reminds me of that part in Royal Tenenbaums, "Everyone knows Custer died at the battle of Little Big Horn. What this book presupposes is, maybe he didn't?"

 

[silverpig]

Originally posted by: Chiropteran
The balloon analogy describes the motion of an expanding universe. I understand that. What I don't understand: where do they get the evidence that the universe is expanding?

See, you are putting the theory before the experimental data that proves the theory. It doesn't work like that, you need to have the data first to build the theory. The expanding balloon analogy is based on the assumption that galaxies further away from us are moving away from us faster. The problem I have is that how do we know they are moving away from us faster? All we know is that they were moving away from us faster when the light we now see was emitted.

For example, a galaxy "A" is 5 billion light years away and appears moving away from us faster than a galaxy "B" which is 2 billion light years away.

BUT, the light we see from galaxy "A" was actually emitted 5 billion years ago! I don't see how we can make any assumption about it's current acceleration based on how it was moving 5 billion years ago. What if it was just moving faster 5 billion years ago because it was still carrying momentum from the big bang, and has since slowed down? I don't see how we could know.

As I said above, a supernova far far away from us is *also* a supernova that occurred a long long time ago. With the information I have seen, it seems like the scientists just assume that the supernova is moving away from us faster because of the distance, while they ignore the possibility that it is moving away from us faster because it occurred a really long time ago and maybe things were moving faster back then.

Basically, I see it as a flawed experiment because there are two different variables- distance and time. How can they know the acceleration is due to distance but not time? I think it's impossible to tell. If all the galaxies were originally moving apart at some incredible speed, but they have been slowing down since the big bang, it would make perfect sense for us to perceive the furthest galaxies as moving faster, because we are seeing the light from them that occurred long ago before they had time to slow down.

We use redshift to determine the velocity that something is moving away from us at. This is the shift of spectral lines towards the red end of the spectrum similar to the doppler shift for sound. Hubble first noticed this and found that objects which were farther away were more redshifted than near objects. This redshift doesn't really come from the motion of the objects in question, but from the expansion of space.

If you emit a photon with a wavelength of 100nm, and space itself expands, the photon's wavelength expands as well, and you might now detect its wavelength to be 110nm.

So Hubble noticed this and came up with a relation for the expansion of the universe called the Hubble constant.

If you have a "standard candle" in the universe, some kind of event which you know is the same brightness no matter where it happens, then you can get an accurate plot of this expansion. From the luminosity (constant for standard candles) and the 1/r^2 dependence of detected flux (measured), you can deduce the distance to the object. You can then take a spectrum and calculate its redshift to find how fast it is moving away from you.

The standard candle is the supernova type 1a. If the Hubble constant is really constant, then plotting the redshifts of observed supernova as a function of distance should yield a straight line, the slope of which is the hubble constant. The Hubble telescope was commissioned with this as one of its major missions. What they found was the redshifts of these supernovae didn't follow a straight line, but a curve which indicated the distant supernovae were moving faster than expected.

This means that as the space between objects increases, so does the velocity with which they move apart. The acceleration of the universe isn't an acceleration that increases with time (although it does...) it's an acceleration that increases with distance (but because the objects are already moving away from each other, it also increases with time).

 

[Chiropteran]

Originally posted by: silverpig
This means that as the space between objects increases, so does the velocity with which they move apart. The acceleration of the universe isn't an acceleration that increases with time (although it does...) it's an acceleration that increases with distance (but because the objects are already moving away from each other, it also increases with time).

How can anyone know that? The only examples we have of great distances are ALSO from a great long time ago. The two variables are locked together.

 

[KIAman]

Redshift doesn't really prove an expanding universe but it does corroborate with a lot of other independent observations. Actually, Einstein tried to apply his theories to our universe and something didn't fit, he was finding the universe was either expanding or contracting but he personally believed in a static universe. So... he added a "cosmological constant" to his calculations that helped his theory apply.

Once Hubble showed some evidence of an expanding universe through redshift, Einstein admitted his mistake and because it was the simplest explanation that corroborated Einstein (and earlier, Newton's) and many other observations and theories, it is now the consensus view of the universe: it is expanding and accelerating as distances get bigger.

EDIT: Simplest solution = Occam's Razor

 

[KIAman]

Originally posted by: Chiropteran

Originally posted by: silverpig
This means that as the space between objects increases, so does the velocity with which they move apart. The acceleration of the universe isn't an acceleration that increases with time (although it does...) it's an acceleration that increases with distance (but because the objects are already moving away from each other, it also increases with time).

How can anyone know that? The only examples we have of great distances are ALSO from a great long time ago. The two variables are locked together.

Hmm, let me give you an example that cannot be described from a time frame difference. A type1a event has a very well known sequence of light and is the same for all type1a events, which is exactly the reason this is chosen as an example.

I don't know the exact sequence but the example still stands (numbers are made up).

Event - Bright light with luminosity of X - lasting 2 days
Event - A curve of diminishing luminosity from X to X-Y - lasting 4 days
Event - Almost a flat line of diminishing luminosity Z - lasting lasting forever

So, it takes about 6 days for an observation of the entire event (remember, these numbers are made up). Now with the stretching of space, a type1a from a great distance now shows the event over a course of 12 days as each individual event takes 2 times longer to view while the closer type1a shows over the course of 7 days.

Even though the further event was much further in the past, the length of the light is all what's needed to determine how much space has expanded from the absolute distance from the event and the observer.

 

[sjwaste]

I guess what the OP is suggesting, though, is that the expansion could have stopped or slowed dramatically, and we won't know for another X billion years (depending on how far away those observed objects were). It's a good point, I just don't think we can observe it directly, so we have to infer.

 

[silverpig]

Oh, and there's no need for your (sic) in supernovae

 

[RideFree]

Originally posted by: KIAman
Redshift doesn't really prove an expanding universe but it does corroborate with a lot of other independent observations. Actually, Einstein tried to apply his theories to our universe and something didn't fit, he was finding the universe was either expanding or contracting but he personally believed in a static universe. So... he added a "cosmological constant" to his calculations that helped his theory apply.

Once Hubble showed some evidence of an expanding universe through redshift, Einstein admitted his mistake and because it was the simplest explanation that corroborated Einstein (and earlier, Newton's) and many other observations and theories, it is now the consensus view of the universe: it is expanding and accelerating as distances get bigger.

EDIT: Simplest solution = Occam's Razor

As I understand the nature of things that used to cause my brain to go "bump-in-the-night", Einstein's "cosmological constant" as applied may actually be required in order to validate that {a} cosmological constant may still be a viable part of cosmology. to wit

 

[RideFree]

Originally posted by: silverpig
Oh, and there's no need for your (sic) in supernovae

Zis is correct!
Superovae is one of the plural forms of supernova...
Or as they say in Spanish, estupendo no go!

 

[f95toli]

Chiropteran: It is an important implicit assumption in astronomy that there is nothing "special" about us (well, the earth). That is, it assumed that we are living on an "average" planet orbiting around an "average" star in a the outer parts of an "average" galaxy. Moreover, it is also assumed that there is nothing "special" about the time we live in. So far this assumption seems to hold, the universe looks more or less the same no matter in what direction we look.

Let's say you are right and some strange event took place a few million years ago making the expansion e.g. slow down; there is no way for us to learn of this fact since our observations are limited by the speed of light. However, a million years is a VERY short time compared to the age of the universe (about 1/13000 to be exact) and not much changes in the universe over such a short timespan. Hence, we would have to be VERY unlucky for this to affect our observations.

Note that there is a another fundamental problem with your line of reasoning, there is stricly speaking no such thing as "simultaneous events" in the universe since time is relative (SR and GR). Hence, from a physical point of view one can argue than an event is "happening now" when the light reaches us; NOT when the light was actually emitted. Basically because it is only then the event in question can have any effect on events here on earth.

 

[KIAman]

Originally posted by: f95toli
KIAman: It is an important implicit assumption in astronomy that there is nothing "special" about us (well, the earth). That is, it assumed that we are living on an "average" planet orbiting around an "average" star in a the outer parts of an "average" galaxy. Moreover, it is also assumed that there is nothing "special" about the time we live in. So far this assumption seems to hold, the universe looks more or less the same no matter in what direction we look.

Let's say you are right and some strange event took place a few million years ago making the expansion e.g. slow down; there is no way for us to learn of this fact since our observations are limited by the speed of light. However, a million years is a VERY short time compared to the age of the universe (about 1/13000 to be exact) and not much changes in the universe over such a short timespan. Hence, we would have to be VERY unlucky for this to affect our observations.

Note that there is a another fundamental problem with your line of reasoning, there is stricly speaking no such thing as "simultaneous events" in the universe since time is relative (SR and GR). Hence, from a physical point of view one can argue than an event is "happening now" when the light reaches us; NOT when the light was actually emitted. Basically because it is only then the event in question can have any effect on events here on earth.

? I never stated the expansion of the universe is slowing down. And if you are referring to simultaneous events when I am talking about the nature of a type1a event, then I suggest you look up a type1a and why it is used as a metric at all.

 

[bsobel]

BUT, the light we see from galaxy "A" was actually emitted 5 billion years ago! I don't see how we can make any assumption about it's current acceleration based on how it was moving 5 billion years ago. What if it was just moving faster 5 billion years ago because it was still carrying momentum from the big bang, and has since slowed down? I don't see how we could know.

You can infer that from the relatively even distribution of mass in the universe. If it had been accelerating faster then and 'slowed' the distribution would be in bands.

 

[f95toli]

? I never stated the expansion of the universe is slowing down. And if you are referring to simultaneous events when I am talking about the nature of a type1a event, then I suggest you look up a type1a and why it is used as a metric at all.

Ops!
Wrong member
That should be Chiropteran (not KIAman), I've edited my post above...

 

[Chiropteran]

Originally posted by: f95toli
Chiropteran: It is an important implicit assumption in astronomy that there is nothing "special" about us (well, the earth). That is, it assumed that we are living on an "average" planet orbiting around an "average" star in a the outer parts of an "average" galaxy. Moreover, it is also assumed that there is nothing "special" about the time we live in. So far this assumption seems to hold, the universe looks more or less the same no matter in what direction we look.

Let's say you are right and some strange event took place a few million years ago making the expansion e.g. slow down; there is no way for us to learn of this fact since our observations are limited by the speed of light.

You have misunderstood my intentions.

I am *not* saying "well yes that galaxy was accelerating away from us 5 billion years ago but maybe it's slowed down and we don't know because the hasn't reached us". That is not my argument.

My argument is this:

Maybe none of the galaxies are accelerating away from us, maybe they are ALL slowing down, and the reason the ones further away seem to be moving faster is just because the light we see is from long ago before they had as much time to slow down.


See, the whole argument in favor for accelerated expansion is that the further galaxies are moving faster. But the problem I have with that argument is that the furthest galaxies are also the ones furthest in the past.

There are two variables, and two possibilities: maybe they appear to be faster because they are further away (this is the common argument), or maybe they appear faster because the light we see from them originated billions of years ago when they were moving faster (this is my argument).

I am absolutely not suggesting that the universe was going through accelerated expansion and recently stopped, not at all. I am suggesting that maybe it started out expanding very quickly (the big bang) and has been steadily slowing down due to gravity since then. Going by that theory, it makes perfect sense that galaxies furthest away from us would appear to be moving the fastest, because we are looking into the past when they still carried a lot of momentum from the big bang.

 

[Chiropteran]

Originally posted by: RideFree

Originally posted by: silverpig
Oh, and there's no need for your (sic) in supernovae

Zis is correct!
Superovae is one of the plural forms of supernova...
Or as they say in Spanish, estupendo no go!

Oops. I thought it was a British spelling or something, until I saw the Wikipedia entry.

 

[bsobel]

The galaxies themselves aren't so much 'moving away' from us, as the space in between is growing, this is what cases the red-shift. This negates the 'maybe they appear faster because the light we see from them orginated.... when they were moving faster'

 

[Chiropteran]

Originally posted by: bsobel
The galaxies themselves aren't so much 'moving away' from us, as the space in between is growing, this is what cases the red-shift. This negates the 'maybe they appear faster because the light we see from them orginated.... when they were moving faster'

No, it doesn't negate anything. Redshift is caused by the source moving away from us. It doesn't matter if it is caused by expansion of space or by the source accelerating away from us in another. It causes the same redshift either way.

The red shifted light we see, regardless of what caused the redshift, originated billions of years ago. So my question stands.

 

[bsobel]

The red shifted light we see, regardless of what caused the redshift, originated billions of years ago. So my question stands.

You need to understand redshift better, the redshift is an ongoing transformation to the light wave that occurred over its entire journey, not when the light was generated.

 

[Chiropteran]

Originally posted by: bsobel

BUT, the light we see from galaxy "A" was actually emitted 5 billion years ago! I don't see how we can make any assumption about it's current acceleration based on how it was moving 5 billion years ago. What if it was just moving faster 5 billion years ago because it was still carrying momentum from the big bang, and has since slowed down? I don't see how we could know.

You can infer that from the relatively even distribution of mass in the universe. If it had been accelerating faster then and 'slowed' the distribution would be in bands.

Huh? That goes directly against the theories of inflation, which say that the reason the universe is so uniform is because of an initial fast accelerated inflation before slowing to "normal" speeds. No offense intended, but you are starting to sound like you have no idea what you are talking about. Do you have a source for your theory that slowing acceleration would cause these bands of mass?

http://en.wikipedia.org/wiki/Cosmic_inflation

 

[Chiropteran]

Originally posted by: bsobel

The red shifted light we see, regardless of what caused the redshift, originated billions of years ago. So my question stands.

You need to understand redshift better, the redshift is an ongoing transformation to the light wave that occurred over its entire journey, not when the light was generated.

I don't really need to understand redshift at all, because I understand relativity. And based on what i know about relativity, light sources 5 billion light years away can only tell us what was occurring 5 billion years ago, nothing more recent. If redshift allowed for faster-than-light travel of information then I would concede the point you are trying to make, but I don't see how that is possible. Regardless of the cause of the redshift, all it can tell us is what the situation was like 5 billion years ago, not today.

 

[bsobel]

Originally posted by: Chiropteran

Originally posted by: bsobel

BUT, the light we see from galaxy "A" was actually emitted 5 billion years ago! I don't see how we can make any assumption about it's current acceleration based on how it was moving 5 billion years ago. What if it was just moving faster 5 billion years ago because it was still carrying momentum from the big bang, and has since slowed down? I don't see how we could know.

You can infer that from the relatively even distribution of mass in the universe. If it had been accelerating faster then and 'slowed' the distribution would be in bands.

Huh? That goes directly against the theories of inflation, which say that the reason the universe is so uniform is because of an initial fast accelerated inflation before slowing to "normal" speeds. No offense intended, but you are starting to sound like you have no idea what you are talking about. Do you have a source for your theory that slowing acceleration would cause these bands of mass?

http://en.wikipedia.org/wiki/Cosmic_inflation

:roll: No it doesn't, cosmic inflation was an event that occurred in a fraction of a second (roughly in 10-33 seconds) where as your discussing slowing over multi-billion year time frames. Over those timeframes slowing would generate banding. Given your example your 5bly distant galaxy would have receeded much further than your 2bly galaxy since the 2bly galaxy has both less time and less acceleration. The result is banding and not the even distribution we see today.

 

[bsobel]

Originally posted by: Chiropteran

Originally posted by: bsobel

The red shifted light we see, regardless of what caused the redshift, originated billions of years ago. So my question stands.

You need to understand redshift better, the redshift is an ongoing transformation to the light wave that occurred over its entire journey, not when the light was generated.

I don't really need to understand redshift at all, because I understand relativity. And based on what i know about relativity, light sources 5 billion light years away can only tell us what was occurring 5 billion years ago, nothing more recent. If redshift allowed for faster-than-light travel of information then I would concede the point you are trying to make, but I don't see how that is possible. Regardless of the cause of the redshift, all it can tell us is what the situation was like 5 billion years ago, not today.

The light wave was generated 5b years ago, the redshift was generated during the ENTIRE 5b 'trip' that light wave took, thats the difference.