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Fraser
2007-Oct-15, 03:00 PM
We interrupt this tour through the solar system to bring you a special show to deal with one of our most complicated subjects: the big bang. Specifically, how it's possible that the universe could have expanded faster than the speed of light. The theory is called the inflationary theory, and the evidence is mounting to support it. Einstein said that nothing can move faster than the speed of light, and yet astronomers think the universe expanded from a microscopic spec to become larger than the solar system, in a fraction of a second.

<strong><a href="http://media.libsyn.com/media/astronomycast/AstroCast-071015.mp3">Episode 58: Inflation (17.0MB)</a></strong><br />&nbsp;<br />

Read the full blog entry (http://www.astronomycast.com/cosmology/episode-58-inflation/)

EvilEye
2007-Oct-15, 11:11 PM
I understand 99% of what Pamela explained, but have a problem with ONE single analogy.

The Little kid walking 4 sidwalk-blocks per second, and then the builders adding sidewalk-blocks between him and the school....

She is adding him to the blocks.

BUT... that wouldn't make him go faster toward school. It would slow him from the perspective of the school. He would have 4 times as far to go if the sidewalk blocks were added in front of him even though he was still moving at the same speed.

A better analogy would be walking on a static mover, like at a theme-park and the people are walking 1 MPH on the mover, but the mover is moving at 1mph. So the person covers twice the distance in the same amount of time.

EvilEye
2007-Oct-15, 11:23 PM
Nevermind... I just listened again. He was walking away from the school, and the block were added BEHIND him.

I get it now.

4tune8chance
2007-Oct-18, 10:11 AM
Tough episode!

I was interested in the comment about the expansion of the universe that it may have pockets of non uniformity, given that these are too far away to be observed, I think it was inferred that the expansion may not be linier.

This got me to thinking, we picture the universe as expanding from a single point out to a sphere. Is it at all possible that the universe is more like a running crack in a pane of glass? i.e. the crack (expanding) but continuing?

Jerry
2007-Oct-19, 06:27 PM
Einstein said that nothing can move faster than the speed of light, and yet astronomers think the universe expanded from a microscopic spec to become larger than the solar system, in a fraction of a second.
The paradox is real, the expansion of space as an answer to this paradox is not. There are energy issues: If the space has increased, then the net gravimetric energy between two objects on either side of the expanded space has also increased, and where did this come from?

Builders adding blocks adds energy, just as an expanding loaf of bread requires energy from the oven. Inflation does not address this energy issue. This explanation for the size of the universe is thermodynamically bankrupt. It is as phony as perpetual motion, and should be summarily dismissed.

EvilEye
2007-Oct-21, 12:28 AM
Perhaps you are looking at it wrong.

Put a tiny marshmallow into a vacuum jar, and suck all the air out. The Marshmallow attempts to fill the entire volume.

There is no lost energy, no gained energy. All the same Marshmallow, just expanding.

That is to say... our universe has no container, so it is trying to fill an infinite volume with finite matter.

Calculon3000
2007-Oct-22, 10:27 AM
Wouldn't it require energy to suck out the air to create the vacuum?

It's the same physical marshmallow, but the properties of it's physical location have changed.

EvilEye
2007-Oct-22, 06:39 PM
Wouldn't it require energy to suck out the air to create the vacuum?

It's the same physical marshmallow, but the properties of it's physical location have changed.

To force the air out of the jar...yes.

But space itself is already a vacuum.

Steve Limpus
2007-Oct-22, 09:55 PM
To force the air out of the jar...yes.

But space itself is already a vacuum.

If inflation is the expansion of space itself, and if you accept that a vacuum requires space (and time), then the jar isn't even really a vacuum, but something...else?

The 'expanding universe' explanation I've most often heard is that spacetime has its own intrinsic 'vacuum energy' or pressure that drives expansion; so as spacetime expands so does the amount of pressure--hence the accelerating universe. It all sounds pretty tidy, but I must confess inflation has always seemed just a little arbitrary. There is something about 'phase transitions' (like when water turns to ice) which sounds appealing as a way to explain the difference between inflation and expansion, that may also be related to the fundamental forces 'condensing' out of the grand unified force. (Think of the universe as frozen energy, cooling from its original hot-dense state. The universe as a giant popsicle!)

I've also heard the 'vacuum energy' of spacetime linked to the idea of 'virtual particles'. I'm sure others more knowledgeable than me can elucidate.

Steve Limpus
2007-Oct-23, 02:12 AM
There are energy issues... where did this [energy for inflation] come from? Inflation does not address this energy issue.

Hey Jerry

It seems science doesn't have a good handle on the properties of the universe prior to the planck epoch, save it was very hot and very dense. Could it be that the energy for everything that has happened to the universe since, was already there at the start?

To me, the idea of the universe condensing out of this unimaginably hot, dense, and energetic state has always appealed. If you compare the young universe to steam: steam doesn't require any energy added to condense into water...the 'steam' actually gives up energy to it's environment in the process, right? I think the technical term is 'exothermic phase transition'. To a lay man like myself, does this address your thermodynamic objection in any way? I still haven't listened to the podcast so I don't know if Fraser or Pamela have mentioned the idea already, apologies if they have.

Of course, the really big mystery would be how did the 'steam' get there in the first place? :shifty:

For me, the 'expansion' of the universe and this idea of 'phase transition' are inextricably linked. Did one somehow cause the other... or each other? And then you have the 'arrow of time.' Its all wonderfully evocative to imagine when I look out at the night sky with my two little boys. (They already love to tell people they're made of Stardust, I think I'll get them to try Condensed Big Bang!)

Anyways... back to work for me... ;)

damian1727
2007-Oct-23, 07:42 AM
In the inflationary theory, matter, antimatter, and photons were produced by the energy of the false vacuum, which was released following the phase transition. All of these particles consist of positive energy. This energy, however, is exactly balanced by the negative gravitational energy of everything pulling on everything else. In other words, the total energy of the universe is zero!

there is no energy lol

great episode really got the flatness problem over well

http://abyss.uoregon.edu/~js/ast123/lectures/lec17.html

BigStan
2007-Oct-28, 07:42 PM
Have enjoyed Astronomy cast for several months but not tempted til now to register and comment--for the purpose of asking: What caused inflation and what halted it? Dr. Gay's reference to "inflaton" particle as causing inflation floored me. I had thought inflation was the "intrinsic" rate of big bang expansion until slowed by emergence of "mass" and gravity, i.e. graviton. If "inflaton" caused inflation, what caused its decay? graviton? Are "inflaton" and graviton related? I'm afraid your Inflation explanation raises more questions than it answered. Why did inflation last 1-33 seconds? What happened to cause expansion to slow to "historic" rates.

Thanks for all the hard work.

Steve Limpus
2007-Oct-29, 04:18 AM
Finally got some spare time to listen to the show--wow! Great work Fraser and Pamela. I was really excited to hear Pamela say that the observable universe is thought to be three or four percent of the entire universe; it's something I've wondered ever since I 'got' the size and shape of the observable universe and our place in it.

If Pamela says its three or four percent that's good enough for me. Does anyone know *how* we figured out that percentage?

Steve Limpus
2007-Oct-29, 04:45 AM
Dr. Gay's reference to "inflaton" particle as causing inflation floored me.

I'm with you Stan--although I read the term 'inflaton' recently rather than hearing it first on the podcast. I'm still trying to 'get' the Higgs Boson, then along comes the Inflaton! So far I've decided the science of inflatons is a bit beyond me yet.

Even Wikipedia doesn't have a lot to say about it:

The inflaton is the generic name of the unidentified scalar field (and its associated particle) that may be responsible for an episode of inflation in the very early universe. According to inflation theory, the inflaton field provided the mechanism to drive a period of rapid expansion from 10−35 to 10−34 seconds after the initial expansion that formed the universe.

The inflaton field's lowest energy state may or may not be a zero energy state. This depends on the chosen potential energy density of the field. Prior to the expansion period, the inflaton field was at a higher energy state. Random quantum fluctuations triggered a phase transition whereby the inflaton field released its potential energy as matter and radiation as it settled to its lowest energy state. This action generated a repulsive force that drove the portion of the universe that is observable to us today to expand from approximately 10−50 metres in radius at 10−35 seconds to almost 1 metre in radius at 10−34 seconds.
I would love it if anyone had a nice simple explanation or link that describes what a 'scalar field' is?

Steve Limpus
2007-Oct-29, 08:42 AM

Hey Damian

That's the thing isn't it. I can go outside and kick the road and its like 'whoa! the earth is big', then I can look at the night sky and 'wow! look at all that...stuff'.

And then, 'where does it all come from?'... and it turns out it is all virtually from 'nothing'.

Or go the other way: the earth is made of atoms, atoms are made of quarks, quarks are made of what? Strings? Nothing?

Way better than any Star Trek episode!

Burt
2007-Oct-30, 02:57 PM
I was really excited to hear Pamela say that the observable universe is thought to be three or four percent of the entire universe; ... If Pamela says its three or four percent that's good enough for me. Does anyone know *how* we figured out that percentage?

Hi Steve. The closest answer that I found is that cosmologists think that the minimum size of the total universe is some 133 billion light years radius. This gives a volume of around 10 billion billion cubic light years. The observable universe has a present radius of about 46 billion light years, giving a volume of about 400 thousand billion cubic light years. The observable volume is then about 4% of the whole.

One must remember though, that the observations are also compatible with an infinitely large universe, which makes the observable portion, well, zero %? :think:

Steve Limpus
2007-Oct-31, 08:58 AM
One must remember though, that the observations are also compatible with an infinitely large universe, which makes the observable portion, well, zero %? :think:

Hi Burt

Are the observations such that the entire universe is either

a: very large (and ours is 4%)
or
b: infinite

or is it just that the very large universe is the miniumum size?

The reason I ask is that the idea of 'infinity' makes my brain explode! I'd be happy to know the 4% deal is a 50/50 proposition.

There's a good show on the BBC World Service website where various experts debate infinity and I get the impression that infinity is a mathematical construct that can't actually exist anywhere in reality. Your example above is a good one: if the entire universe is infinite then the observable universe is 0% - and yet here we all are, and it is rather a lot of stuff! (Actually I'm not sure about the maths--is it 0% or just an 'infinitely' small % but not quite 0?)

I'm gonna buy 4% - at least I'll be able to sleep nights! :)

A Brief History of Infinity: Space and the Universe
http://news.bbc.co.uk/2/hi/programmes/documentary_archive/5349064.stm

A Brief History of Infinity: Mathematics
http://news.bbc.co.uk/2/hi/programmes/documentary_archive/5349364.stm

Burt
2007-Oct-31, 09:42 PM
Hi Burt

... or is it just that the very large universe is the miniumum size?

The reason I ask is that the idea of 'infinity' makes my brain explode! I'd be happy to know the 4% deal is a 50/50 proposition.

Hi Steve.

Yea, infinite size doesn't really make sense, does it. I think present observation indicates that the universe is at least 25 times the size of the observable universe (which is then at most 4% of the total). The universe may possibly be millions of times larger than our observable patch, but no one knows just how BIG and we may never know.:(

Burt

damian1727
2007-Nov-04, 11:01 AM
as i understand it no one has any idea how big our ''bubble is beyond the observable universe.....tho i have heard much much larger estimates then 25 0/0...... one i liked i cant remember where from was that the observable universe was the size of a photon then the entire bubble was the size of the earth.....

but no one knows... (apart from douglas adams)

but to cut a long story short if the edge of the universe is receding from us faster than the speed of light then it is to us on any practical level unending

?

i love this stuff

lol

Steve Limpus
2007-Nov-05, 12:10 AM
but to cut a long story short if the edge of the universe is receding from us faster than the speed of light then it is to us on any practical level unending

Yep.. I get that. Interesting way to think about it.

I read somewhere that there will be future civilisations who will be unable to observe the universe beyond their own gravitationally bound galaxy (or perhaps cluster?) because everything else (even the CMBR) will have receded beyond the Hubble limit. I don't know all the details, or if the timing is such that the universe is likely to support intelligent life at that time, but it's a sad thought: entire civilisations who can never know the rest of the universe exists... I wonder what they will make of things?

Burt
2007-Nov-06, 03:49 AM
I read somewhere that there will be future civilisations who will be unable to observe the universe beyond their own gravitationally bound galaxy (or perhaps cluster?) because everything else (even the CMBR) will have receded beyond the Hubble limit.

Hi Steve.

Yes, according to present theory, this may happen in the unforeseeable distant future! I do not think that the CMB will ever drift 'out of view', so to speak, but it may just become so redshifted that it is undetectable. Sad...

Steve Limpus
2007-Nov-07, 01:35 AM
Came across these quotes:

"...the entire universe is expected to be at least 1023 times larger than the observed universe! ...if the inflationary theory is correct, then the observed universe is only a minute speck in a universe that is many orders of magnitude larger." Alan Guth (found this in a post from Cougar on this thread: Episode 28: What is the universe expanding into?)

"It is also possible that the universe is smaller than the observable universe. In this case, what we take to be very distant galaxies may actually be duplicate images of nearby galaxies, formed by light that has circumnavigated the universe. It is difficult to test this hypothesis experimentally because different images of a galaxy would show different eras in its history, and consequently might appear quite different.
A 2004 paper claims to establish a lower bound of 24 gigaparsecs (78 billion light-years) on the diameter of the universe, based on matching-circle analysis of the WMAP data. This is a lower bound (not an estimate) for the size of the whole universe (not the observable universe). If the universe is smaller than the observable universe, then light has had time to circumnavigate it since the big bang, producing multiple images of distant objects in the sky. Cornish et al looked for such an effect at scales of up to 24 gigaparsecs (78 billion light years) and failed to find it. 24 gigaparsecs is simply the upper limit of the search space of this study; it has no physical significance." http://en.wikipedia.org/wiki/Observable_universe#Size

...so I guess this really is one of those no-one really knows things.

Here's another question: if the idea from the Wikipedia quote above were correct (that apparently distant galaxies are actually earlier images that have circumnavigated a compact universe) would we then observe the same apparent recession of those apparently distant galaxies? I wouldn't have thought so - but it does illustrate that there isn't one really satisying answer yet (ever?).

CPMosh
2007-Dec-02, 06:31 PM
Someone, please help me understand the expansion of the universe. As space expands, are there more units of distance between objects or are the units of distance getting bigger? If the units get bigger, will the amount of units (meter sticks) between objects will remain constant?

How many meter sticks will fit between the sun and another star now as compared to a billion years from now?

If the units of measure are getting bigger (the same number of growing meter sticks), does light cover less of them in a certain period of time (light’s time based on a fixed size meter stick)? What do we have remaining as our frame of reference?

If the units of measure are getting bigger, how is the expansion of the universe to be distinguished from light simply getting slower over time?

If the units of measure are not getting bigger, how is this distinguished from a simple explosion of matter into existing space?

Thank you

NHR+
2007-Dec-02, 10:12 PM
I think the expansion occurs only in larger scales, galaxy clusters or something like that. Individual stars in a galaxy are not moving away from each other, or they sure can be, but that's not due to the expansion of the universe. Andromeda galaxy is also "comin' right for us", only all of the "far-far-away-galaxies" seem to be receding. Galaxies and galaxy clusters (local group, Virgo cluster?) are called "gravitationally bound", if they're not moving away from each other. I'm not sure just where exactly this boundary lies...

I guess it's rather that there would become more room for "metre-sticks" than the sticks themselves expanding. Light in the process gets redder, that means its wavelength is increasing.

Also, in an explosion of matter into pre-existing space, there would be some kind of center point visible, I suppose...

Not very helpful now, is it... ;)

damian1727
2007-Dec-02, 10:18 PM
?

errr the space between stars is expanding

units of measurment are a human conveniance and have no physical reality.....tho i guess a light year is a unit of measurement,,,,

as space expands there will be more light years between objects

light is not getting slower

things would have to be shrinking as well lol...well u never now...

the simple answer is yes you are correct as the universe expands there is more distance between things....

errrrrr

:/

CPMosh
2007-Dec-03, 02:32 AM
Okay, so units of measure are staying constant while space expands. Based on this, what would happen in this example?

Suppose NHR+ purchases one Megaparsec of rope at the hardware store. The rope is carefully measured out at 2×10(to the)19 miles. Frasier takes one end and Pamela takes the other. They move off in opposite directions.

Now, as I understand, the length of the rope stays consistent (relative to the speed of light?), so once Pamela and Frasier get the rope taught, they have to hold on pretty tight as the expansion of space tries to pull them apart at 73.5km/sec (correct?).

What do we observers in the middle see happen if damian1727 sneaks up with scissors and cuts the rope. How fast do the ends move apart? What do Frasier and Pamela experience out on the ends?

What if the test is repeated with a 2 Megaparsec piece of rope?

Thanks to you both for jumping in and helping clear this up.

Steve Limpus
2007-Dec-03, 08:41 PM
...so once Pamela and Frasier get the rope taught, they have to hold on pretty tight as the expansion of space tries to pull them apart at 73.5km/sec (correct?).

I don't think they would have to hold on 'tight'.

The strong and electro-magnetic forces of the atoms and particles of the rope (and of Fraser and Pamela) would easily overcome the expansion of space and they would hardly notice--just like we don't notice here, nice and comfy in the Milky Way, where (even the incredibly weak) force of gravity also easily overcomes the expansion of space.

I imagine Fraser and Pamela easily hanging on with one hand, and chugging back beers with the other. (What happens when you crack a beer in a vacuum?)

73.5km/sec sounds violent, but I'm pretty sure if you state the expansion of the universe as a percentage it would seem pretty small and 'gentle'? The expansion of the 'local' space around Fraser for example would be very small--it's only when you sum the expansion over a large volume of space that the velocities become large? Kinda like compound interest?

And it's not like Fraser or Pamela are moving through space at 73.5km/sec--rather space itself is gently expanding at 73.5km/sec per megaparsec... or something. :shifty:

"...the cosmic microwave background radiation that we see right now was emitted about 13.7 billion years ago by matter that has, in the intervening time, condensed into galaxies. Those galaxies are now about 46 billion light-years from us, but at the time the light was emitted, that matter was only about 40 million light-years away from the matter that would eventually become the Earth." http://en.wikipedia.org/wiki/Observable_universe

So our observable universe has expanded by over ten thousand percent, but has taken over ten billion years to do so--thats about one ten thousandth of one percent per year... I think? :doh:

damian1727
2007-Dec-03, 09:24 PM
snip snip lol i always get the good jobs

i dont know any figures but they could as steve said hold the rope easy but if the rope was very very long and i waited say 100 years even tho pam and steve had not moved(after chugging beers 4 100 years who could blame them!!) i would not be able to join the ends up......

lol

i know its a small effect on the local level but it must be happening in my house !!!

a little?

Steve Limpus
2007-Dec-03, 09:51 PM
What do we observers in the middle see happen if damian1727 sneaks up with scissors and cuts the rope. How fast do the ends move apart? What do Frasier and Pamela experience out on the ends?

This is my (barely) educated guess...

If Fraser and Pamela bought the rope on Earth, and flew off 0.5 Mpc in opposite directions: I suspect they wouldn't experience anything unusual (except a marvelous view) because they would still be within the gravity well of the local galaxy cluster.

If we had all teleported to a large void, and were not bound by any local gravitational system: we observers in the middle of the rope would observe Pamela and Fraser receding at 36.75km/sec (and they, us); Fraser and Pamela would observe each other receding at 73.5km/sec, but they would not experience any acceleration, just the expansion of the space between them. Whether the gravity of Pamela, Fraser, the rope, and we observers, would make a difference I don't know... but I expect such a little mass (how much does a Mpc of rope weigh?) over such a large distance would make little difference (due to the inverse square law).

...relativity might have something to say about it too? And red-shift etc.

I suppose you just 'times two' if you double the length of the rope.

Steve Limpus
2007-Dec-03, 09:57 PM
I know its a small effect on the local level but it must be happening in my house !!!

...Beer, or the Hubble Constant? :)

damian1727
2007-Dec-03, 10:36 PM
lol

if we get more space are we loosing time?

its all to do with between a and b but thats funny

and how do point particals...with no internal parts (as they are fundemantal)... interact?.... on the quantum level a place seems to be a fuzzy idea..?

if we live in a world of gravitons and ''fields'' is there any such thing as space time or just relations between things....

and how does a stupid monkey that believes in now and then and here and there make any sense of a universe where light lives in the real world ??

*?*

no here no there no way to tell one place /time from another.....OH!! like a perfect void of nothingness.....perfect symetry

shoot me

lol

:)

Steve Limpus
2007-Dec-03, 10:38 PM
How fast do the ends move apart?

If Pamela and Fraser are each still holding on to their end, and we're standing (floating?) next to Damien and his scissors, and we observe Pamela and Fraser receding at 36.75km/sec... then both (cut) ends of the rope will eventually accelerate to 36.75km/sec away from us, depending on the elasticity of the rope... unless the inertia of the rope is somehow greater than the Hubble Constant, in which case we wouldn't observe Pamela and Fraser receding???

...someone pass another beer? :confused:

damian1727
2007-Dec-03, 10:45 PM
now the bloody rope is elastic ?? lol o ****

and it has inertia????? you said inertia *faints*

Steve Limpus
2007-Dec-03, 11:32 PM
Even my cat doesn't get Quantum Mechanics.

And he knew Schrodinger.

Apparently.

CPMosh
2007-Dec-04, 01:08 AM
Let's say that the rope doesn't stretch.

Before the rope is cut, how does expanding space appear to Pamela and Frasier? Suppose each is in a location with bits and pieces of debris. Suppose the debris is stationary relative to that grid of space. Is this debris flying by Pamela and Frasier at 36.75 km/sec?

How much tension is in the middle of the rope before it is cut?

How much time is required for Pamela and Frasier to reach 36.75 km/sec away from damian1727,with his scissors, after the rope is cut?

If the rope doesn't stretch, how long does it take the information that the rope has been cut to reach Pamela and Frasier, putting an end to their game of (gentle?) tug of war?

What happens if NHR+ gets a longer rope...lots longer. Now the rope is so long that Pamela and Frasier see debris moving past them in their respective grids of space at the speed of light! Can each feed out more rope and see things go by even faster? Will time go in reverse if it does?

Steve Limpus
2007-Dec-04, 03:44 AM
Let's say that the rope doesn't stretch.

Before the rope is cut, how does expanding space appear to Pamela and Frasier? Suppose each is in a location with bits and pieces of debris. Suppose the debris is stationary relative to that grid of space. Is this debris flying by Pamela and Frasier at 36.75 km/sec?

How much tension is in the middle of the rope before it is cut?

How much time is required for Pamela and Frasier to reach 36.75 km/sec away from damian1727,with his scissors, after the rope is cut?

If the rope doesn't stretch, how long does it take the information that the rope has been cut to reach Pamela and Frasier, putting an end to their game of (gentle?) tug of war?

What happens if NHR+ gets a longer rope...lots longer. Now the rope is so long that Pamela and Frasier see debris moving past them in their respective grids of space at the speed of light! Can each feed out more rope and see things go by even faster? Will time go in reverse if it does?

I'm pretty sure we can't say the rope will not stretch - even it was a steel rod - it's made of atoms like any other matter. Even a neutron star stretches. I think. (Never tried! :))

Information can travel up and down the rope no faster than c (the speed of EM which binds the atoms together - in fact less I think, as light slows down in matter e.g. refraction in a prism).

If the rope were longer, so long it would in theory extend to regions of space which were receding at greater than c, there would be no way to get Pamela and Fraser there, they can't travel faster than c either, so would never catch up.

I suspect relativity would prevent our experiment even with the 1 Mpc rope (my brain hurts if I try to figure it out). Maybe the only experiments you could do in nature would involve light - which is what astronomers do every day when they observe distant galaxies anyway. Maybe there is an experiment you could devise involving cosmic rays, which from memory are massive particles traversing space at near c. The only other place you could observe particles at relativistic speeds is an accelerator - which would be way too small to observe the Hubble Constant, and which is gravitationally and atomically bound anyway. Or maybe something with gravitational waves - perhaps when LIGO goes into orbit?

So, my guess for the debris problem is - Pamela and Fraser will never observe the debris 'cos they can't (really) get there. If we stay with a thought experiment - I'm tempted to say the debris would be flying past, and there is no 'extra' tension due to the expanding universe. But I'm sure there is some reason everyday intuition is wrong, some reason that invalidates the experiment on some level.

Steve Limpus
2007-Dec-04, 04:08 AM
How much time is required for Pamela and Frasier to reach 36.75 km/sec away from damian1727,with his scissors, after the rope is cut?

It would take 1.6 million years for Damian to observe the effect--0.5 megaparsec=1.6 million light years. This is why I think nature invalidates the experiment in some relativistc way - no one can chug beer for 1.6 million years...

CPMosh
2007-Dec-04, 04:53 PM
What if Frasier decided to toss the long rope and come up with something lighter. He makes a Megaparsec piece of Nanotube and coils it up. The tube is driven over to Pamela's house where they sigh and pick an end to take for their next game of tug of war. The first thing they notice is that the tube is getting 73.5 km shorter each secord! How do you grab that and pull?

Clearly I don't have any idea what I am talking about. What would really happen?

The gap in my understanding (in a field of many) touches on an issue that I think Steve brought up in another inflation discussion. Are the units of dimension (say planck length) inflating between two points or are there more unit being squeezed in over time.

Please correct me where I fall off track here. We have inflating space as a model for the expansion of the universe. Would shrinking matter (and decelerating light) work as an alternate model? Could the size of the Universe be constant while the matter within it shrinks, and appears to grow further apart?

Steve Limpus
2007-Dec-04, 07:32 PM
What if Frasier decided to toss the long rope and come up with something lighter. He makes a Megaparsec piece of Nanotube and coils it up. The tube is driven over to Pamela's house where they sigh and pick an end to take for their next game of tug of war. The first thing they notice is that the tube is getting 73.5 km shorter each secord! How do you grab that and pull?

Clearly I don't have any idea what I am talking about. What would really happen?

The gap in my understanding (in a field of many) touches on an issue that I think Steve brought up in another inflation discussion. Are the units of dimension (say planck length) inflating between two points or are there more unit being squeezed in over time.

Please correct me where I fall off track here. We have inflating space as a model for the expansion of the universe. Would shrinking matter (and decelerating light) work as an alternate model? Could the size of the Universe be constant while the matter within it shrinks, and appears to grow further apart?

The best I could find out was 'we don't know how space expands' but I got the impression the planck length probably isn't changing. I wonder if we could even tell - wouldn't one have to be 'outside' the universe to observe it? The best guess seems to be that vacuum energy and/or virtual particles somehow expand space--then there is even more space, more energy/particles, and space expands even more. The effect must be weaker than the electro-magnetic and strong nuclear forces, and stronger than gravity only on the largest scales. Something similar (or not?) is said to be responsible for inflation - but tied up with thermal (like?) phase transitions, like water changing to ice, when gravity condensed out of the super-force? If the universe ends in a Big Rip - then expansion/dark energy eventually wins somehow...

Of course I could have no idea what I'm talkin' about too! I usually get only so far and my brain melts - or it's time to mow the lawns. :lol:

I like your rope conundrum. I'm still thinking about it - maybe others will chip in?

Maybe I need to go listen to Fraser and Pamela's show again - unfortunately there weren't any show notes with the Inflation episode - I've found they usually help!

NHR+
2007-Dec-04, 08:42 PM
I've been trying to think about this CPMosh's "rope conundrum", and I have to say I just don't know WHAT would happen. All real ropes (or nanotubes, for that matter) would HAVE to be somewhat elastic, and also I don't think there really is (or ever will be) any ropes some megaparsecs in length... think about the sheer mass of such a rope! But thinking it just as a thought experiment... my brain still seems to shut down. :wall:

Interesting thought, though.

I don't think shrinking matter and decelerating light would do very well as an alternate explanation, but anything "scientific" to base this "gut-feeling" on, that's totally beyond me, of course...

CPMosh
2007-Dec-05, 01:07 AM
Where do we stand so far?

Would our coiled-up Megaparsec-long nanotube contract at 73.5 km/sec? Imagine the coil flipping around, in the back of Frasier's car on the way to Pamela's house, as the nanotube gets shorter.

Or... What if the coiled nanotube didn't contract? Pamela and Frasier straighten the tube and do find, however, the expanding space drifts by each (now distant) end at 36.75 km/sec (relative to the center of the nanotube).

Are there a boatload of observations that the shrinking matter (and decelerating light) model fails to explain? Would the alternate model rescue us from the need for a Dark Energy concept?

Forgive me for flogging this horse. I am grateful to everyone for taking the time to help explain this.

Fraser
2007-Dec-05, 06:32 PM
There's a transcript for the inflation episode now:
http://www.astronomycast.com/cosmology/episode-58-inflation/

Steve Limpus
2007-Dec-06, 12:16 AM
Where do we stand so far?

Would our coiled-up Megaparsec-long nanotube contract at 73.5 km/sec? Imagine the coil flipping around, in the back of Frasier's car on the way to Pamela's house, as the nanotube gets shorter.

Or... What if the coiled nanotube didn't contract? Pamela and Frasier straighten the tube and do find, however, the expanding space drifts by each (now distant) end at 36.75 km/sec (relative to the center of the nanotube).

Are there a boatload of observations that the shrinking matter (and decelerating light) model fails to explain? Would the alternate model rescue us from the need for a Dark Energy concept?

Forgive me for flogging this horse. I am grateful to everyone for taking the time to help explain this.

Ok. I'll have another crack at this... fortune favours the bold!

As long as the nanotube is in Fraser's truck - or anywhere in the Milky Way (or any other galaxy) - it ain't gonna shrink. Space does not expand within gravitationally or electro-magnetically bound systems like trucks or galaxies. I'm not shrinking. You're not shrinking.

Space is thought to be expanding on the largest scales due to observations of distant galaxies.

The current theories relating to the 'expansion of space' and the 'Big Bang' are well accepted by the scientific community. Even Hoyle (who hated the Big Bang 'til his dyin' days) was able to deduce the nucleo-synthesis of atoms heavier than hydrogen and helium because he also observed the expansion of the universe. (Hoyle's 'mistake' was only that he thought matter was generated somewhere in space in a 'Steady State' universe - it was later discovered the heavier atoms were generated inside stars.)

Somewhere (I don't know where the 'boundary' would be) this expansion effect (dark energy?) overwhelms gravity and the galaxies are observed to recede. I think astronomers caluclate for expansion even when they observe Andromeda, which has a net velocity towards us.

As far as I know, these observations are all really real.

But we don't know how space expands. Max Tegmark (I think) described Dark Energy as simply a name for our ignorance. It's even possible Dark Energy is nothing more than a slight misunderstanding of Gravity. But I don't think scientists anticipate any major problems with our concept that the universe is expanding... people like Brian Greene are on the cutting edge of stuff like String Theory and I've never heard them even suggest a problem with expansion.

I've never heard an 'expert' talk about light slowing down or matter shrinking either - but hey, I'm just a science fan, not a scientist.

Just my \$0.02 - and I love to debate this stuff... :)

Going back to our rope, in the void...

We can imagine Fraser is in a bubble of space which *pop* becomes bigger--and at the same time Pamela's bubble of space *pops* too.

I don't imagine that any debris (or any particles) that share Fraser's bubble are suddenly rushing past - why would they?

But... what has happened to the rope?

I imagine the distance between Fraser and Pamela is larger. Light travelling between them is red-shifted. No problem.

Ok. I imagine that, because every 'bubble' of space along the megaparsec of rope has also *popped*, the net effect has overcome the electromagnetism of all the atoms that make up the rope, and the rope has stretched. There are a heap of atoms along that rope and they can each, all handle being stretched apart a little. One day, they'll be too stretched and the atoms will fly apart.

There's the Big Rip astronomers talk about.

We can probably observe a kind of rope stretching today - the filaments that make up the structure of the universe we see in things like the Sloan Digital Sky Survey.

Any good?

CPMosh
2007-Dec-06, 01:48 AM
Wow, Steve. You know stuff! I have lots of homework, looking into the various theories: pops, space filaments, and space bubbles at the end of long ropes. I intend to spend quite a bit of time with your answer, but first...

Please everyone, bear with me while I get the following concept off my chest. What if the universe started out at its present size, absolutely filled solid with matter. Crazy? Well, it gets worse. The big bang (fizzle?) occurs, and matter starts to decay; to shrink. No expansion. The shrinking, decaying matter clumps and swirls around together, making slowly decaying galaxies all across the stable-sized universe as time passes.

From our perspective, or at least my pathetic perspective since I don't have any idea what I am talking about, the grid of space appears to be expanding. Our frame of reference seems stable, so we assume that it is space that is doing the changing. Matter would not have to decay (shrink) perceptably to make a HUGE megaparsec of space seem only 73.5 km/sec bigger. Maybe we wouldn't even notice since everything made of matter which we perceive shrinks too, except space!

This helps me with two troubling concepts in particular. Pamela, in the inflation show, was talking about the peculiar homogeneity (sp?) of space in all directions. This would not be as irksome if everything was already spread out across the stable sized universe. It is just the spaces between things that appear bigger. With any luck, the model also relieves us of Dark Energy. Again, with everything already out there, we don't need this mysterious (to me) force shoving it all apart.

I am trying to figure dark matter into my ridiculous unified theory, but I haven't.

Whew, thanks for listenting to this nonsense. Please, no one needs to waste time explaining all the ways this is a ridiculous concept. I know, surely it is like some kid asking why their dog can't be president of General Motors.

Out to Pamela and Fraser (I got the spelling right this time), thanks for the show. It even appeals to someone who knows as little as I do.

Steve Limpus
2007-Dec-06, 03:19 AM
Hey CPMosh.

I know what you mean about the homogeneity and flatness of the universe. Alan Guth came up with 'inflation' to explain it... otherwise, working back from the expansion they see today, astronomers figured the universe should look heterogeneous and curved. Inflation always seemed a bit convenient and arbitrary to me--but if you google 'sonic waves in the cosmic microwave background' there is a bunch of esoteric research by really clever people - and they all seem perfectly happy. So who am I to worry?

Damien doesn't think any of it's real - he figures we're all a figment of his imagination! Something like that... :lol: Hi Damien.

Does anyone like the *popping* space bubbles? I wouldn't mind betting when/if they do figure out how space expands - it'll be some kind of quantum effect.

*pop!*

...oops, sorry, that was just my soda. :shhh:

CPMosh
2007-Dec-06, 04:30 PM
I am trying to understand the pop hypothesis.

To summarize, we have a megaparsec-long piece of straignt rope in an otherwise empty part of space. The question is, are the ends of the rope, with Fraser and Pamela hanging on, flying through their respective grids of space at 36.75 km/sec or are they stationary within their grids while the rope stretches? If the rope is stretching, at what connective level does it do so?

The pop hypothesis doesn't seem to rely on the length of rope at all. Each bubble is expanding irrespective of whether it is connected to another bubble, or lots of other space bubbles.

It seems that the pop theory has the expansion on the atomic level. This is somewhat confusing. I thought I understood that the electromagnetic force simply laughed at the inflationary force. Does this also mean that the planck length is inflating?

The rope can stretch on a variety of levels. The filaments of rope can pull apart or break. The molecules within the rope can separate from one another. The atoms within the molecule can pull apart into separate elements. The protons, neutrons, and electrons within the atoms can pull apart. The quarks and up quarks and down quarks can pull apart. I am sure I left something out. Where does inflation do its work under the pop hypothesis? It sounds like the current pop theory relies on the atoms falling apart.

Here I go again with another ridiculous example. What, instead of the rope, a whole bunch of fist-sized stones were found in a tremendous line. The stones are touching each other and in a megaparsec-long straight line. Is there expansion in the chain? Where is it? Do the stones get further apart? The stones are only touching; no glue. There is nothing to resist tension. Do the stones break apart over time as the molecules fall apart? Do the elements within the stone disassociate? Does each stone grow slightly larger and less dense as the atoms get bigger? Do the parts of atoms get bigger? Do the spaces within the atom get bigger?

Do the forces within matter which usually laugh at expansion eventually grow exausted and submit to the pop?

Steve Limpus
2007-Dec-07, 01:40 AM
I am trying to understand the pop hypothesis.

To summarize, we have a megaparsec-long piece of straignt rope in an otherwise empty part of space. The question is, are the ends of the rope, with Fraser and Pamela hanging on, flying through their respective grids of space at 36.75 km/sec or are they stationary within their grids while the rope stretches? If the rope is stretching, at what connective level does it do so?

I think Fraser and Pamela are stationary with respect to their local space ('bubble' of space as I imagine it)--just like the Milky Way is. At least as far as expansion is concerned--we're not considering spin or tidal forces or any of that good stuff.

If we think of our rope as just atoms, not molecules and all that complicated chemical stuff, I think it stretches at the level of the electro-magnetic bond between atoms--which is why I think we can compare it to the concept of the Big Rip--at some time in the distant future the atoms fly apart when they can't stretch no more. I think this is kinda comparable to the red-shifted light astronomers observe--when you think about it, photons are the force carrier of electro-magnetism, and light is photons too... my thinking is that the electromagnetism, like light, just gently stretches to accomodate the increase in distance. Red-shifted light, at least, we already observe.

I think all this would look nice and soft and gentle to an observer if we could see the whole length of the rope at once (which we can't because of relativity). I think if we consider how long the rope is, compared to how much it stretches - it's a tiny percentage. I reckon the entire observable universe expands about one ten thousandth of one percent over a whole year. So in other words - our rope ain't expanding much. We could stretch a rope ourselves that much right here on Earth, and you and me are only very small regions of quarks, gluons, electrons and photons.

The pop hypothesis doesn't seem to rely on the length of rope at all. Each bubble is expanding irrespective of whether it is connected to another bubble, or lots of other space bubbles.

The universe is expanding everywhere, all at once, except where gravity (mainly gravity because it is a force that acts at a distance, but also the other forces I suppose) is holding it back. I'm dividing up space into bubbles to help me imagine what might be happening where Fraser is, and where Pamela is. We could imagine dividing space into bubbles up and down the entire length of our rope, and suppose that they are all expanding simultaneously.

It seems that the pop theory has the expansion on the atomic level. This is somewhat confusing. I thought I understood that the electromagnetic force simply laughed at the inflationary force. Does this also mean that the planck length is inflating?

Not even on the atomic level perhaps? It's space (spacetime) that is said to be expanding, so in other words the 'background' on which all particles and forces exist - I'm thinking more of red-shifted light now, which is a real observable phenomenon.

Remember - I don't think nature really has to worry about actual megaparsec ropes 'cos they don't exist.

Space is the background - but it also interacts with particles and forces, for example via electromagnetic fields. And, I'm thinking particles are also wave-like, and waves happily expand every day, just like at the beach. And we know that space happily bends and curves and stretches... General Relativity tells us so and we (well not me!) have tested it. Heaps. I suspect somewhere in all of that stuff, is the mechanism whereby space expands, whether its vacuum energy, virtual particles, dark energy or some screw-up with gravity. But we don't know.

On the scale of atoms, Frasers, trucks and galaxies - the 'normal' forces do laugh at expansion, 'cos after all, we aren't expanding, at least not in any meaningful way anyone has observed. On the largest scales, distant galaxies are all receding from each other, apparently due to the expansion of space between them. Astronomers see it through their telescopes. I think we have to go with that.

I don't believe the planck length is changing at all. The reason I don't believe it, is that I've never seen or heard of any evidence that it is. But I have often wondered, like you. I've concluded, even if it were changing, we wouldn't know, because any measure stick we could devise, would be changing exactly the same, and so would we.

The rope can stretch on a variety of levels. The filaments of rope can pull apart or break. The molecules within the rope can separate from one another. The atoms within the molecule can pull apart into separate elements. The protons, neutrons, and electrons within the atoms can pull apart. The quarks and up quarks and down quarks can pull apart. I am sure I left something out. Where does inflation do its work under the pop hypothesis? It sounds like the current pop theory relies on the atoms falling apart.
Here I go again with another ridiculous example. What, instead of the rope, a whole bunch of fist-sized stones were found in a tremendous line. The stones are touching each other and in a megaparsec-long straight line. Is there expansion in the chain? Where is it? Do the stones get further apart? The stones are only touching; no glue. There is nothing to resist tension. Do the stones break apart over time as the molecules fall apart? Do the elements within the stone disassociate? Does each stone grow slightly larger and less dense as the atoms get bigger? Do the parts of atoms get bigger? Do the spaces within the atom get bigger?
Do the forces within matter which usually laugh at expansion eventually grow exausted and submit to the pop?

The Big Rip hypothesises first galaxies, then solar systems, then planets, then atoms, then all matter... is torn apart by the accelerating expansion of the universe. Then time stops. Apparently. But it's all hypothetical. Like our rope. Try this link perhaps?

http://www.space.com/scienceastronomy/big_rip_030306.html

The *pop* is just how I have imagined the expansion, 'cos I've never seen it myself. It could be smooth and classical. If it were quantized (we don't know) it could really be a *pop* from a certain point of veiw. To paraphrase Obi-Wan. :)

I don't know how we would line up our stones, any more than I know how we would make a megaparsec rope.

There are plenty of stones in space, but all the stones we can see are in our galaxy and wouldn't count. If a comet or meteor, or even a planet, somehow got chucked into an intergalactic void where there was no gravity (there would probably be some?) - I don't imagine that anything particular would happen to it any time soon.

We're much better off sticking with light.

I'd be more inclined to look at the Sloan Digital Sky Survey, then look at it again later (much later if possible) and observe what has happened to the great voids, and bubbles, and filaments and sheets of galaxies and galaxy clusters that make up the structure of the universe.

There's our rope.

http://www.sdss.org/background/science.html

Steve :think:

I need a lie down.

Steve Limpus
2007-Dec-07, 04:19 AM
...and matter starts to decay; to shrink. No expansion. The shrinking, decaying matter clumps and swirls around together, making slowly decaying galaxies all across the stable-sized universe as time passes.

While I was having my lie down... a thought occurred. We know matter decays by the weak nuclear force. So, if we suspected we were living in a shrinking universe--space would be filled with the same kind of radio-activity we would find at an old atom bomb test site? And if we were shrinking, or at least our atoms or quarks were--wouldn't we display some pretty odd characteristics?

... oh crap, I'm glowing! :eek:

eddyfca
2007-Dec-08, 05:34 AM
We need an episode one this, and I'll have a beer while I listen to it.

Steve Limpus
2007-Dec-08, 12:12 PM
We need an episode one this, and I'll have a beer while I listen to it.

http://curious.astro.cornell.edu/question.php?number=274

This is good... check out the idea of a tape measure to a distant galaxy, that when you wind it back is longer than a similar tape measure in your pocket. This stuff is always mind bending, but I find if I stick at it, it really is as elegant and beautiful as the scientists say.

Steve Limpus
2007-Dec-08, 12:15 PM
...beer is mind bending too, of course. :)

CPMosh
2007-Dec-09, 10:33 PM
It seems that we can make a few concrete determinations about inflation, or stretching. “Curious about astronomy” was really helpful in that it proposes a stretching tape measurer, much like our (NHR+’s) rope.

It seems that the general agreement is that the stretching (not expansion) is happening on the electromagnetic level. It also seems that it makes no difference how long the rope is because each local “bubble” of space is stretching from within.

The rope has no tension along its length. A megaparsec rope has its ends moving apart at 73.6 km/sec, and they are accelerating as the ends get further apart. Even a 6-0 long piece of rope expands at this same rate; the tension on the rope is irrelevant. Length is irrelevant.

So we have it, the expansion of the rope, or tape, or nanotube, can be measured by the collective stretching of space within and between atoms. The little electromagnetic “ropes” between particles on this level are getting stretched by one ten thousandths of one percent per year. Inflation is continually overwhelming the electromagnetic attraction between particles. This percentage increase in space within and between atoms is admittedly pretty small, but we have a lot of years to experience the effects.

But, how can this be? Even the weak force of gravity is able to resist inflation. And it does so indefinitely (correct?). The “rope”, Gravity, doesn’t seem to weaken over time. It either keeps warps space enough to get things to pull together, or it doesn’t and they move apart (or appear to move apart).

How much longer can a nanotube “rope” get? Can the effect of inflation eventually break the bonds within or between atoms?

This example seems distinct from a tense chain finding the weakest link to break. The stretching model, from within, doesn’t seek out the weakest link. Tensile strength of the material is not a factor. The whole chain has to break (fall apart, inflate, expand, stretch, HELP!) at the same time.

Those websites are a fantastic resource. Thank you, Steve, for providing so many resources and introducing such well-worded and informative proposals of your own. It has been truly gratifying to find a community so intrigued with these topics.

Steve Limpus
2007-Dec-10, 03:26 AM
The little electromagnetic “ropes” between particles on this level are getting stretched by one ten thousandths of one percent per year. Inflation is continually overwhelming the electromagnetic attraction between particles. This percentage increase in space within and between atoms is admittedly pretty small, but we have a lot of years to experience the effects.

Except... there aren't really any tape measures or ropes between galaxies. We would find any real tape measure or rope we could ever observe will be quite happily 'laughing' at expansion, as you said. Like here on earth. We're invoking hypothetical tape measures and ropes. But, we can easily see light from across the cosmos, and it really is stretched (red-shifted).

As we were trying to imagine our rope I was struck by the similarity of our problem to the idea of the Big Rip - but - as far as I can tell, the Big Rip is just as hypothetical as our rope, and I'm not entirely sure why its proponents think expansion will eventually overcome electromagnetism and the strong nuclear forces (both of which act at short range, unlike gravity).

The key to the idea of the Big Rip tearing apart atoms, then quarks, then stopping time (I don't even pretend to know what that means!) seems to be that expansion is presumed to accelerate indefinitely. Presumably this acceleration causes the 'force' of expansion to become ever greater at ever shorter distances?

Galaxies and planets vaporising is kinda hard to picture... only Darth Vader would call that a good day!

Aside from all of that, the expansion of the universe isn't due to atoms expanding, it's due to the space between galaxies expanding (stretching). Thats what we would see if we observed the great sheets and filaments of galaxies and galaxy clusters that make up the universe: the space between the galaxies stretching.

Perhaps our hypothetical rope overly complicates things... it sure does make one think!

But, how can this be? Even the weak force of gravity is able to resist inflation. And it does so indefinitely (correct?). The “rope”, Gravity, doesn’t seem to weaken over time. It either keeps warps space enough to get things to pull together, or it doesn’t and they move apart (or appear to move apart).

Gravity resists expansion, but doesn't defeat it over large scales, hence distant galaxies recede. The force of gravity decreases due to the inverse square law; so over long distances it becomes so weak, galaxies recede. If we imagine gravity to be a 'rope' hooked to a distant galaxy, at both ends the rope doesn't stretch. In the middle, where gravity is weakest, the expansion of space prevails and the rope slowly stretches. But now we're mixing metaphors... oh the humanity! :silenced:

As far as I can tell many astronomers don't think expansion will actually start tearing atoms apart; they think expansion will slow, or at least it won't accelerate for ever. They figure the galaxies will eventually drift apart so that a future civilisation here in the Milky Way would look out into space and observe nothing beyond our own galaxy... the other galaxies will all be beyond the Hubble Horizon, so far away the light would never catch up. This seems a bit more intuitive than the Big Rip. But... eventually matter decays (due to the weak nuclear force) until nothing is left - it all just evaporates away. A good day for the Dark Side. :evil:

...or, the expansion reverses and everything ends in a Big Crunch or Big Bounce. Another bad day for Luke. :lol:

How much longer can a nanotube “rope” get? Can the effect of inflation eventually break the bonds within or between atoms?

This example seems distinct from a tense chain finding the weakest link to break. The stretching model, from within, doesn’t seek out the weakest link. Tensile strength of the material is not a factor. The whole chain has to break (fall apart, inflate, expand, stretch, HELP!) at the same time.

Big Rip proponents I think would say yes, expansion eventually breaks atoms... and that seems to be the conclusion when we compare our hypothetical rope or tape measure to light. Light really does stretch. We have to assume our rope or tape measure would also stretch. Is the comparison valid in reality, or is it just a useful analogy? Light is made of photons not atoms, after all. I don't think we should worry too much. Nature seems to have made matter (visible matter at least) into galaxies, stars and planets... not ropes and tape measures. :)

Perhaps our rope is comparable to what would happen to our atoms if we fell into a Black Hole... where our atoms would apparently be stretched apart, like spaghetti, and perhaps even broken?

Consider this - if we did actually pull apart an atom, then try to pull apart the quarks which make up the proton: the strong nuclear force gets stronger with distance, until there is so much energy trying to pull the quarks apart it just makes more quarks! What would that do to our rope!!!

Something else to consider is that we (or at least the scientists!) probably don't have all the tools to work this out. Relativity works well for things like galaxies. Quantum Mechanics works well for things like atoms. The two do not work together. This is a problem for the Big Bang, Black Holes, and the Big Rip. In other words, perhaps science doesn't yet have a complete theory to describe our scenario?

Perhaps check out CERN and the Large Hadron Collider on the web as well - they fire it up next year. Physics is only gonna get even more mind-blowing!

Those websites are a fantastic resource. Thank you, Steve, for providing so many resources and introducing such well-worded and informative proposals of your own. It has been truly gratifying to find a community so intrigued with these topics.

Welcome. It's nice to chat. I'd be rapt to think my meager understanding might have helped a fellow traveller, I only hope I haven't made things worse!

My wife says it's all ** and the kids just want to know if I'm finished 'playing' on the computer yet! :lol:

Here's a couple more websites you might like: