The Universe: Faster or Slower Expansion?

I like to think of the analogy of the universe being on the outside surface of a balloon!

If you put dots on a balloon and blow it up you can easily see the dots expanding away from each other at different rates.

The closer ones move away from each other slower than the farther ones.

Similarly with an explosion (big bang?) All the dots at one point back in time would be at one point in space, a singularity, after the bang the points (galaxies?) all move away from the centre.

John.

The balloon analogy does not quite illustrate the situation.The light from the distant side of the balloon takes billions of years to arrive at your telescope,so all you can say for certain is that a billion years ago, that particular part of the galaxy was accellerating.We have no idea exactly what that galaxy is doing right now..it may be extinct for all we know., or consumed by it's central black hole, or merged with another galaxy....A billion years ago, the universe was younger, and it stands to reason that it may have been still accellerating,but the newer information (closer stars) indicate a lesser velocity, which would appear to me that the expansion is slowing.We are doomed to read yesterday's news when it comes to the universe, unless we can find a way to circumvent the speed of light, via a wormhole or some as- yet- undiscovered method.

HiTekRedNek

The discovery of the acceleration was made by two independent teams. Each team was essentially performing the same experiment... They were studying a type of very well known star within fairly local galaxies. Because the properties of these stars is well known, it allowed the researchers to determine both distance and speed of the galaxies to a very precise degree. Both teams of researchers discovered a decidedly distinct acceleration.

Furthermore, I believe all the space-time and Hubble effects were accounted for in their data, and still the acceleration was there. The whole astrophysical community pretty much agreed with the results, and they're still scratching their heads about what is causing this. Hence, a lot of astrophysicists are proposing a fifth physical force.

The VERMIN ANSWER WAS THE SECOND PART OF THE SCIENCE CHANNEL ANSWER that showed that the universe is expanding at an increasing rate, i know it sounds abserd but there must be a hidden new force that is causing this effect, dark matter that is put in motion may through various preasures or Gravety & Magnitism MAGNIFIED DUE TO SPEED cause a increase in speed, though the direction can fluxuate due to preasures also. IF the object can be studied for long periods of time consecutively there may be seen fluctions in direction as speed increases.

Hi vermin, you wrote: "... I believe all the space-time and Hubble effects were accounted for in their data, and still the acceleration was there. The whole astrophysical community pretty much agreed with the results, and they're still scratching their heads about what is causing this. Hence, a lot of astrophysicists are proposing a fifth physical force."

Yes, provided the that so-called "Lambda-cold-dark-matter" model of the cosmic expansion is the correct one, a whole host of observations support the increasing expansion rate, making cosmologists look for the "dark energy" that causes it.

However, one must always be careful not to read too much into model-dependant findings: models have toppled over in the past! Having said that, I side with Einstein's "biggest blunder", his cosmological constant that he used to keep his universe from contracting. It's probable just Einstein's "blunder" that pushes the expansion to go faster and faster...

I wrote a short mini-series on my CR4 Blog some time ago. http://cr4.globalspec.com/blogentry/456/Cosmology-Equations-Part-4 has something on the cosmological constant.

Regards, Jorrie

Jorrie,

Point taken! I concur :-)

I'm a simpleton and view the world - or in this case, the universe - from a simpleton's perspective. If one were to introduce a small amount of gas into a large vacuum chamber, would not the particles of gas accelerate as they rushed to fill the chamber?

Viewed from the perspective of any electron in the bit of gas released, the "universe" would be undergoing cooling and expansion at an accelerated rate.

I realize being one of six or seven billion observers on an electron does not help the astrophysicist's ego.

Hi jdst, you wrote: "Viewed from the perspective of any electron in the bit of gas released, the "universe" would be undergoing cooling and expansion at an accelerated rate."

I think your premise that the electrons would accelerate is correct! In fact, this somewhat resembles the epoch of "cosmic inflation" in the standard cosmology of the day. However, this inflation epoch lasted for only 10^-34 seconds; the rest of the 10+ billion years, the particles were not rushing away from each other.

According to prevailing theory (backed up by observations, to a large extent), the first 5 billion years or so were characterized by a gradual decrease in the expansion rate. Then, if we take observations at face value, the expansion rate started to increase again. Not heavily, just barely perceptibly. Complicated, horribly complicated, you might say?

There actually are rather simple considerations that led to the present state of cosmological theory. I pointed a few of those considerations out in my CR4 Blog on Cosmology Equations.

Regards, Jorrie

Jorrie: Is this too simplistic, and possibly all wrong? Imagine a set of many small magnets, dispersed in a sphere of some gas or similar that will support the megnets, but not retard their movement (call it space-time). Give each magnet a steady, continuous, very small force outwards from a central starting point. As the magnets slowly increase in distance from each other, wouldn't the "attractive forces" between magnets (magnetism here, but gravity in the real Universe) diminish slowly on a distance/time scale, but the constant initial, long acting force pushing the magnets apart would gradually accelerate the magnets away from each other at an ever increasing, but slow, rate. It seems to picture an accurate scenario of what we see, but I may be missing a lot! It would make a nice computer-generated storyboard for Nova, et al. Thanks for any insight.

Hi Cardio-2, your magnet analogy is not too far off the mark, given that the magnets must not move through the gas, but the container must expand and with it the gas, carrying the magnets further apart.

In the best models we have, the container got an initial rapid expansion (inflation epoch) after which it kept on expanding, but at a decreasing rate. Until, at some point something started to add energy to the gas and the container start to expand faster again (like the presumed dark energy of the cosmos).

The is a very imperfect analogy, but as good as the balloon or the raisin bread analogies. However, what is interesting in this one is: if magnets were close enough to each other, their mutual attraction would overwhelm the expansion of the container/gas and they would clump together (like galaxies and clusters do). On larger scales, the expansion overwhelms the attractive force.

Beware of thinking that each magnet has something pushing it - it is the gas that is being "pushed" to expand. In any case, it is better to think along the lines of the infinite lattice that I posted some time ago.

Regards, Jorrie

In your example, if the tank was large enough, the momentum of each atom would keep them moving outward (within a "perfect" vacuum) until they reached the walls of the tank. There, they would either bounce off or be absorbed by the tank material.

However, what no one has mentioned here is that the Universe is not a bunch of outward traveling objects expanding into an open void. Instead, what we see as "expansion" is that space itself is getting larger. I know that this is a strange idea to fathom, but all the mass and energy that's moving away from each other because of the Hubble Expansion, are doing so because space is getting larger. Accordingly, a billion years ago objects in the Universe were closer because space was actually smaller.

This may add a bit more understanding about why the acceleration is considered so important: things are accelerating because space is getting larger at an accelerated rate. Woof!

You said:"They were studying a type of very well known star within fairly local galaxies."

Are you referring to Cephids? If so, these same stars are also used to calculate the age of the universe, and according to the latest data, something is amiss....some stars appear to be older than the universe.This cannot be, so the information from these stars is dubious, or innacurate.

The best estimate to the LMC, which is key to all distance measurements using Cephids, is plus or minus about 10 percent.This includes the various methods of computation, including RR Lyrae Stars,Main Sequence fitting,Eclipsing Binaries, TRGB,Red Clump,and Mira Variables.The most recent calculations, based on Supernova 1987A give the distance to the LMC as ranging from 44-51 Kpc.

The perceived expansion rate is less than the margin of error.

Hi HiTekRedNek, if Vermin will pardon me for answering, I understood what he said as: astronomers use Cepheids and Supernovae in the local galaxies to characterize those stars. They are then used to measure the distance to the more and more distant ones and hence the expansion rate over time. The local galaxies, like LMC do not show the expansion of the universe at all; in fact, Andromeda comes straight at us!

The accuracy of the direct methods are probably no better than 10%, as you said. Cosmologists use this data, together with other measurements that are independent from the distance (i.e., the CMB radiation spectrum) to estimate the age and expansion curve of the cosmos to <1% levels. I must add that those very accurate estimates are cosmological model dependent, so when the model is revised the estimates change!

Regards, Jorrie

YOU HAD TOO METCH TEQUILA last night, This Was just on the science channel and the expansion is going faster as time goes by, they showed that the huge explosions that occured 20 years ago are still expanding and the shock waves are traveling at a faster rate than they started which proved the universe is expanding at a faster rate.

Please expand on the huge explosions to which you refer...how far away were they from earth?

Thanks

THE SHOW Science nova show displaied a dieing star exploding 20 years ago there was a ring of marerial traveling out from the center.

This ring was traveling out at a constante rate and after 10 or 18 years the rate of expansion was increasing in expansion speed there was the thought that the universe is expanding in an increasing rate.

Si,Senor, I did indeed, but in the sober light of sunrise it dawned on me (pardon the pun) that the similar poles of a magnet repel each other at a certain distance, however, if one is much stronger than the other, when brought into close proximity, they do indeed attract and stick together.Could matter have a similar propertywhen applied to the scale of the universe? Attractive at a certain range,(gravity) and repulsive at long range? Maybe I should not have eaten the worm in the bottom of the bottle.........

"Question:Why do astromomers say that the universe is expanding at an accellerating rate?"

Maybe we're not finished blowing up yet . . .

As Jorrie so eloquently and elegantly demonstrated with a drawing by his son, the universe as a whole can be expanding at a constant rate, yet the furthur we look away , the faster it seems to be moving.Consider this example:You are a flea on a compressed spring.you are on the bottom coil, looking up.The tension on the spring is released at a constant rate, and the coils are moving apart at 1 inch per hour.

If you looked at a nearby coil, you might not notice that it is getting furthur away all the time, but look up at the 1000th coil, and you would see that it is moving at the combined speed of all the previous 999 coils, plus it's own speed, or 1000 inches per hour.This would be more noticeable.And the more coils between you and your focal point, the faster they would appear to be moving.Likewise, a light beam shone from the coils would show a progressive red-shift as the distance away from you progressed.The universe as a whole may not be accellerating, but the combined effect of all the individual components of spacetime (whatever they are) expanding at a constant rate, can give the appearance of accelleration.This hints at a connectivity of all parts of the universe.This is an oversimplified illustration of the way I see it.

As always,I could be wrong.

HTRN

Hi HTRN, thanks for the compliment!

You wrote: "The universe as a whole may not be accelerating, but the combined effect of all the individual components of spacetime (whatever they are) expanding at a constant rate, can give the appearance of acceleration."

Yep, the appearance can be there, but if the spring analogy is used at a constant rate of expansion of coils, the farther coils will always be moving away faster than the nearby ones - for a constant expansion rate!

The universe seems to be a bit more weird than that - the rate of change of the distance between adjacent coils seems to be on the increase! This means that the distant coils are farther away form us than what a constant, or decreasing, expansion rate predicts.

This is the essence of an increasing expansion rate - whether it is true still needs to be confirmed... (IMO)

Regards, Jorrie

Applying the known laws of physics, if something is expanding, (a balloon?) there must be an increase in internal pressure(due to heat, or more matter,energy, etc) or a decrease in external pressure.Perhaps our universe is gaining energy or matter at a faster rate than in the past, or the "outside" pressure is decreasing at a faster rate than in the past.Considering that the effect of the expansion is only noticable at 100 million light years or more, then we do not really have any current information on what is happening right now.If a scientist in the Hydra Galaxie sent you a telegram, at the speed of light, telling you the rate of the expansion in his corner of the universe, it would be billions of years before you got the message.Would you trust that information as holding true today? Perhaps instruments today are a lot more sensitive at detecting red-shift, and this could account for the perceived accellerated expansion?Looking at a graph of Hubbel's law, the expansion looks pretty linear with distance to me.Of course, the graph may not be true to scale, or may not have been updated to reflect the latest data.

And as always, I could be wrong.

I will not argue the fact that the smaller balloon has a higher pressure at rest, but the point Iwas making is this:If you attach a pressure guage to the large balloon while it is enlarging,the pressure will increase above the pressure before you started increasing it's size.(not nescessarily greater than the small balloon) Once stabilized, the pressure will settle out .If our universe is expanding, and not static, there has to be a driving force either internal or external.If it is accellerating, the internal force must be increasing, or the external force decreasing.Perhaps the force is induced from an external source, the way a secondary of a transformer collects flux from the primary and produces voltage as a result.We may be "riding" a sine wave on the rise, or something similar.If we could live long enough, we might see the universe "exhale" again. We only have a snapshot, in galactic terms, of the state of the universe, and we cannot presume that it will always expand just because of our short-term studies.

Hi HiTekRedNek, you said: "Perhaps the force is induced from an external source, the way a secondary of a transformer collects flux from the primary and produces voltage as a result."

Who knows? Maybe not from "outside" our 'Hubble bubble', but maybe from another dimension invisible to us?

Regards, Jorrie

It doesn't matter what, where or when the driving force behind the expansion of the universe is or was, it is within the universe. It may not be within the known universe but it must, by definition be within the universe as a whole.

By definition the universe is all encompassing and anything that exists is within the universe. It doesn't matter if it is within our sphere of detection or not, if it exists or has an effect it is part of the universe and that includes all energy, matter, time, space, gravity or anything we may or may not learn about.

By your definition of universe ,(anything that is, was, or will be) which is accepted by many, I must agree.

However, if you poke your finger into the ballon, and do not puncture the membrane, is your finger part of the inside of the balloon, or is the indention simply considered an effect of something from outside? Of course, by your definition, there can be no "outside", since if it is there, it must be within the universe.

To me, personally, this is too easy. A refusal to think outside of the balloon.I consider, and mind you this is a personal opinion, so are they all, personal opinions, the universe to me means: All space, matter, and energy that occur within a single (or "n") hyperplane(s).

There are many planes or dimensions outside of the ones we exist in.A 4 dimensional sphere is called a GLOME ( this exists in tetraspace), then there is Pentaspace,with 5 dimensions, etc.etc,.

Please do not be offended or feel challenged by my opinions, I am simply giving them air (or whatever the atmosphere).

I do not disparage nor belittle your opinion, for all have equal weight in their parent's eyes, and parents are quick to defend their offspring.I try not to spoil mine by protecting it from the world at large.If you want to know the truth, sometimes you have to throw out all things that are sacrosanct and challenge the status quo.

The only thing faster than light is imagination.I can cross the galaxy in almost no time at all, and walk on alien soil, and breathe alien air,and thrive on sunlight from a blue star, and look upsilon into an alien star-filled night and wonder, as I look wint towards the constellation of a trionian dragon, if there be any other life forms out there , looking back at me.

Respectfully,

HTRN

Hi HTRN

What I was trying to convey is that there can be only one true universe. There may be subsets that for example you and I may only see as a so called observable universe, but for something to be universal it muse encompass, as you said, everything that ever was, is or will be.

In your balloon for example somebody on the inside of the balloon may see the inside as their observable universe but that doesn't make it the true universe. The true universe must also encompass your finger, you, the floor you are standing on, the building you are in, the planet the building is on an so on.

For our science we normally use some sort of subset as it makes things easier to explain but if you find for example energy coming form nowhere then the boundaries you have set for the universe are too small.

I don't think the universe is infinite either, I believe it has a finite limit to matter, energy, space and time and that we are constrained within those limits by the physics of the universe. If however we were to find that energy, mass, time or space were leaking in or out through a black hole for example then the boundaries we have set are too small. In this case we would need to expand them to include wherever or whenever the energy matter, space or time is coming from or going to. We may never be able to go there but we can't go to the stars we now see at the edge of the visible universe either but we don't exclude them.

All this comes back to why I say the true dimensions of the universe are matter, energy, time and space. Yes we use three numbers to describe a particular position but this is just a convention that we have adopted. To encompass everything in the known universe you need to use mass, energy, space and time rather than length, depth, height and time.

At a fundamental level the universe usually turns out to be elegantly simple. Just look at the way energy and matter are tied together with the equation E = mc². The equation is so simple yet it has mind boggling consequences. Ultimately I believe we will find that all four are tied together, in a similar and equally as elegant and fundamental way, as energy is to matter. It just seem to me to be a logical conclusion.

Now all of this doesn't even get the status of a theory as it isn't based on anything but an idea and there is no mathematical model or explanation. Unfortunately my mathematics and physics is way too underdeveloped to analyze this but that doesn't stop it being something that is worth discussing. Who knows, maybe somebody that dose have the skill will be able to either prove or disprove it?

Now I have a splitting cosmolograine so I am going to call it quits for the time being.

Sorry about your headache.You look up at night and see the Southern Cross, I look up and see the Big Dipper.Our perspectives are different, yet we see the same universe, simply different aspects of the greater whole.

May peace, tranquility, and contentment follow you wherever you go, and may you never forsake wisdom in your quest for knowledge.

Sincerely,

HTRN.

"Beer is the proof that God loves us."

-Benjamin Franklin

Masu and HTRN,

I think I can resolve your respective differences, unfortunately it may end in semantics.

Masu, at one time (not to long ago) astronomers believed that the Milky Way was the Universe. However, once other galaxies were discovered, astronomers were faced with the idea that the Universe was a whole lot bigger than previously believed. And now, they think that there may be many universes (small "u"), of which ours is just one... Hold that thought!

HTRN, you are saying that if there are these multi-verses, then what's between them isn't space, but something quite different. And each Universe is self contained, and the term Universe is not appropriate to describe the set of all multi-verses.

Back to Masu - When the Milky Way was seen as not the Universe, scientists expanded the term to represent all the space that contains all the observable stuff and then some. But consider that the definition of the Universe was expanded to include all that was in our space bubble, which was considered to be infinite. However, the new thought regarding the Universe is that it's a closed system. There's no way to move beyond its physical spatial limits. So, you're redefining the word Universe (big "U") to mean the set of all multi-verses, which now stands for "everything."

While HTRN is saying (I believe) that since universes (little "u") are bounded, we need to come up with a new word to stand for the set of all multi-verses and all the whatever is between them, as opposed to changing the definition of the word Universe.

Perhaps we can agree to call our local universe the Universe (or U), and the total of all multi-verses Universe' (or U' {Universe-prime}). Would that work?

How about "Interactive Universe" which includes everything that we can see or detect plus everything that has a measurable effect on what we can see or detect and "Overall Universe" which encompasses everything detectable or not.

That'll work, too.

Hi masu, isn't "everything that we can see or detect plus everything that has a measurable effect on what we can see or detect and "Overall Universe" which encompasses everything detectable or not." just the distinction between our observable universe and the Universe?

Hi vermin, I think the U' idea is not bad, but AFAIK, the term multi-verse is normally taken to consist out of more than one universe (which is a unitary concept), with Universe meaning "our universe", like Galaxy means our galaxy.

I propose that we somehow stick to the generally used conventions.

Regards, Jorrie

Jorrie,

Yes, that was what I was trying to get at... The Universe that we're stuck in (as far as we know) is our local Universe. However, there may be many "island" universes outside of our own. And each contains its own inhabitants. It is this set of all these Universes that I was referring to by the term "multi-verse."

Because I am unqualified in the field of astronomy and barely have my life together well enough to get through the day, I find the question begging to be addressed by the blurry visions of my mind before going back to sleep. From what I have seen of the night sky from the vantage point of a comfortable slab of concrete a few yards from my front door that seemed to far to crawl to until dawn, I would say the astronomers have it all wrong. The universe is not so far away as they think. Everything appears smaller in the distance because the light emanating from objects spreads out in all directions and thus at a distance things appear smaller, but they aren't. Big telescope lenses are needed to make objects at a distance appear bigger and closer. The universe in the east always seems to be drawing closer while the universe in the west seems to be retreating in the western sky. This phenomena is amplified by the season of the year and the movement of our local universe out at the fringe of this Galaxy. A bowling ball, angrily thrown off a cliff while throughly intoxicated seems to grow smaller as it plummets into the sea. Thus the universe is explained to my satisfaction. I would like to add, however that unexplained phenomena is best left that way. Gravity has never been explained to my satisfaction so I decided to think of gravity as just another cultural myth. I couldn't stand the vacuum of not having some sort of explanation for the phenomena for very long...its like trying to stand up and walk in a straight line in front of a cop. Gravity must be explained. Here's mine...there is no gravity, the universe is exploding and the rate of this explosion just happens to be 32 feet per second per second. This has been going on since the dawn of time and eventually we'll be moving at the speed of light and all matter will vanish. On a distance world far far away, drunks looking up at the night sky from the comfort of a slab of concrete will observe the flickering light of our world exploding at the speed of light and will think..another star is born.

And if you believe in fairies, please clap your hands!!!

I think that all these analogies are as faulty as thinking of an atom as a tiny solar system. If you're going to make progress with the accelerating expansion, you have to take a different approach. Something like Einstein's General Theory or quantum mechanics... My quark needs an oil change.

Actually, the big problem is the refusal of astrophysicists and mathematicians to accept that they cannot know, model, compute nor comprehend the universe. Human hubris. Why can't the solar system be a little atom in a bigger thing which itself is a bit in a bigger thing etc.? And why can't this work both ways?

What I find difficult to accept is that space - which is nothing - is expanding. How do you know? When was space smaller - and how do you measure the size of ... nothing. Better still, how do you measure the size of nothing, particularly at a time when you aren't there, in order to determine the nothing is growing now when we seem able to measure nothing. Besides if nothing is becoming bigger, then something must be getting smaller, no? Or does something and nothing have to balance?

All this space hurts the space between my ears. It is shrinking, but there is more space there now than before.

The thing that drives a lot of people crazy is the question "What is space?" I know it really makes my last, remaining neuron hurt!

However, space IS actually something, but as science discovers more and more, it's one of those somethings that exist only as a relationship of other things...

I always loved this analogy: matter and energy on a subatomic scale is like a rainbow. You can see it, measure it in the sky, image it, and perform a bunch of other experiments on it. However, if you try to go running after the rainbow to physically get a hold of it, it isn't there; it doesn't exist. The rainbow is a real thing, but it's one of those things that exist only as a relationship among other things.

That blows my Mind!!!

HiTekRedNek in post #18 stated,

Applying the known laws of physics, if something is expanding, (a balloon?) there must be an increase in internal pressure(due to heat, or more matter,energy, etc) or a decrease in external pressure

Actually as a balloon expands the pressure decreases. The pressure in a balloon is the greatest as it just starts to expand and the least just before it bursts.

If you don't believe this take a balloon and blow it up paying particular attention to how hard it is to blow up with each breath. You will find that it is considerably harder to blow up at the beginning and with each subsequent breath it gets easier.

sabo in post #16 stated,

Everything appears smaller in the distance because the light emanating from objects spreads out in all directions and thus at a distance things appear smaller, but they aren't. Big telescope lenses are needed to make objects at a distance appear bigger and closer.

With a star it's diameter is so small compared to the distance it is away that no matter how big the telescope or how much magnification is employed stars always appear as points of light.

The speed that a star is receding is not measured by how fast it is changing position but by how the light is shifted in frequency. As you may know if the light from an object that is moving will change frequency proportionally to the speed that it is moving with the frequency increasing for approaching stars and decreasing for receding stars. By measuring this change in frequency you can easily measure the speed that any object is moving.

Hubble found that the further a star was away the greater the frequency shift and therefore the faster it was moving. If you now look at the ratio between the distance a star is away and the speed that it is receding at you will get a constant that strangely enough is called the Hubble constant.

Sorry Masu, but the pressure increases as the balloon fills. While there may be some initial resistance to stretching that requires a higher pressure to overcome, once inflation has begun, the pressure must increase to increase the size. Otherwise when you let air out, the balloon would grow.

Hi Jst,

Have a look at this link and then see what you think afterwards.

I can see this stretching into another inflated CR4 discussion!

Cool. Now you know I am going to have to find a way to a) try it, and b) measure the pressure in the balloons. That'll take me months.

I have been trying to either find or remember the proof but if I remember correctly it comes down to the overall force in the balloon increases in a linear manner in relation to the radius while the surface area increases as a square. Since the surface area is increasing more rapidly tan the force constraining it the pressure actually decreases as the volume increases.

I think this illustrates the :"Rising Bubble" illustration in another way.Weather balloons are not filled all the way at launch, because as they rise, the atmospheric pressure drops, and they will expand, but for a different reason.The ballon in the link that you provided describes the effect as due to a finite amount of elastic force, spead over a larger, and larger area (The rubber membrane becomes thinner). As this force becomes more dispersed, the total pressure per unit decreases.I will admit though, that at first glance, the result of the balloons is counterintuitive.

Onward and upward could be a simple explanation of lambda.

So many theories and analogies!

I like the balloon analogy, but the internal pressure is equal to the external pressure + the compressive force of the membrane between blows - ie an equilibrium is achieved.

With the magnet theory, the attraction would reduce - if I'm correct - by the square of the distance between attracting objects, so unless the spinning effect would increase to increase the attractive forces, then the acceleration would increase dramatically.

Any pictures of galaxies show them in near 2D - what caused the big bang to explode in only two dimensions? Are there two giant, invisible dinner plates either side of the known universe stopping expansion in the third dimension? this may account for the increase in acceleration, as the pressure in the centre of the universe reduces, the plates would be drawn inwards, pushing the matter outward faster.

What is this mystical pressure that everyone is talking about. Look, you've got to move away from "everyday analogies." Seems like everyone is locked in the 18th Century! You can't use these Newtonian models to describe space-time. That was Einstein's big breakthrough!

Space-time is not a balloon, nor a tank of gas, nor a membrane, da, da,da...

Hi vermin, why so hard on us? The balloon and other analogies do normally help people to understand some aspects of cosmology better, as long as one recognise the limitations of the analogy...

BTW, the "mystical pressure" is, in a way, the doing of Einstein himself! His cosmological constant (lambda) can be described as a negative pressure that causes the accelerated cosmic expansion. If lambda is non-zero, it really sucks...!

From Wkipedia: "In physical cosmology, dark energy is a hypothetical form of energy that permeates all of space and has strong negative pressure.^[1] According to the Theory of Relativity, the effect of such a negative pressure is qualitatively similar to a force acting in opposition to gravity at large scales. ..."

Regards, Jorrie

Yes, I generally agree with you, but while these analogies may work for layman science (meaning you really don't understand in the first place, and "I" {whomever} don't want to spend the time to bring you up to speed), they lead one far astray if followed for any distance. Again, the "epicycle" concept (let em know if you want more on epicycles).

Anyway, even when Einstein performed his thought-experiments, he kept clear of Newtonian analogies. He knew that he was dealing with something that had no resemblance to Newton's "Clock-work Universe." The idea of "negative pressure" is another one of these analogies. Gravity is the curvature of space-time. Now, one has to find that which un-curves space-time. And not a pressure in any way related to thermodynamics. That's why they create giant super-collides, and don't bang rocks together.

Also, this is why Einstein was the murderer of the "Ether." He said if you can't measure it of detect it in any way, I DOES NOT MERIT ANY MORE THOUGHT - IT DOES NOT EXIST AS FAR AS I AM CONCERNED. So far, he's been proven correct.

To understand space-time, it's necessary to shed Newton and sore on the wings of Einsteinian physics... at least for the time being.

I'm having fun!!! How about you?

Hi vermin, it's always fun on this forum!

You mentioned Einstein's thought-experiments; his cosmological constant was not a though experiment, AFAIK. When he first applied his field equations to cosmology, he discovered that a static universe is impossible - it had to expand or contract. I guess you know all this... I also guess that Newton could have come to the same conclusion! Hmm...

Point is, Einstein's negative pressure is not quite an analogy in the sense that the balloon is. It is something that can be measured on the very largest scales and the negative pressure model fits the measurements. Positive cosmological pressure curves space-time more and visa versa for negative pressure.

Having said that, I prefer to talk about vacuum energy density and not negative pressure, or even worse, dark energy! But they are just different terms for essentially the same thing.

Regards, Jorrie

This "pressure" or whatever you want to call it is not the point. The point is what is actually being affected by the pressure. In this case, the pressure is not pushing all the stars, galaxies, etc. away from each other. Instead, the pressure is making space, itself grow larger.

Spacial objects moving by momentum are moving in all sorts of different directions. For example, the Andromeda galaxy is headed straight for us. If the pressure was pushing all matter away from the big-bang, then we could easily see where the big-bang occurred in the Universe. However, because the Hubble-effect is only associated with how fast space is expanding, everyone sees themselves as the center of the expansion.

Consider the galaxies, clusters,stars, etc. as all within the bubble, and gravity, momentum,etc., is still free to act upon them as it does now,so the individual motions would not nescessarily all be linear or outward in direction, however, spacetime itself (the bubble in this scenario) is expanding in all directions outward.

Seems to fit, IMHO.However, as always, I am always open for other ideas, and accept constructive criticism in the benevolent and instructive manner in which it is intended.

With the "Balloon analogy," the matter in the Universe is represented by a bunch of dots on the outside skin of the balloon. As the balloon is blown up (it has to be in order to make the analogy work), the dots get farther away from each other and each dot sees itself as the center of expansion. That's how the analogy works in two-dimensions only. However, as far as any material inside the balloon is concerned(3-D stuff), the analogy breaks down.

If you're going to think about the expanding Universe, then you must make the nasty, intuitive leap of thinking of a three-dimensional surface that's expanding. Also, all objects on the expanding three-dimensional surface are free to move about any way they want.

The point I'm trying to make here is that whatever the force is (or just the nature of space), it works on space itself and not directly on the matter in the Universe.

I understand what you are saying, and I agree, but I fear that I am not expressing my idea very well.The matter within the "bubble" is free to move as it is influenced by gravity, static, magnetic, electrical, etc., forces, but the space between the matter is becomes less dense, and expanding.The matter is irrevokeably attached in some manner to the "filling" (spacetime?) of the bubble, and must be pulled along with it as it expands.So in a way, I guess we are saying the same thing, it's just my way of mentally picturing a 3 dimensional surface.

Thanks for the feedback. Every reply causes me to think deeper about my ideas, and to question them.All people tend to treat their ideas as their children, but I try not to spoil mine by making them immune to correction and constructive criticism.

This is the real freaky part of Universal Expansion... I can see why you use this concept in the analogy, but space is not becoming "less dense." Just so we're clear. Space can't become less dense, there's just more of it in all 3-dimensions. Pretty wild!!!

Hi vermin, I suppose HiTekRedNek's analogy is just about the "Hubble bubble", i.e. our observable universe with diameter two Hubble radii.

When you said "Space can't become less dense, there's just more of it in all 3-dimensions", were you referring to the "ordinary" definition of space, where "empty space" has no mass?

The energy of "empty space" is obviously not zero, it sports "vacuum energy" or quintessence, or whatever. This is apparently the dominant form of energy in the universe. Whether the energy density of the vacuum is precisely constant still needs to be proven, AFAIK.

Regards, Jorrie

Years ago in an article in Scientific American, it was stated that if you could make a perfectly sealed piston and cylinder, then pump all the air out to form a perfect vacuum, you could not get the piston to go all the way to the top of the cylinder because of vacuum energy or zero-point energy. So, I know about that.

Also, empty space has a measured resistance and capacitance. However, space isn't something you can hold or touch. When you ask a physicist or astrophysicist what space is, their answer, like the rainbow analogy, is it is not a thing. Rather, it's existence is based on a relationship. As far as I know, while they are proving that space is expanding (Einstein even knew it was capable), no one has proved that the zero-point energy, resistance, or capacitance is changing.

Hmmm!..........Interesting..........more info to assimilate....

RESISTANCE IS FUTILE ("The BORG") ......now about the capacitance .....

Thinking...............

Thinking.............

What are the characteristics of a gas bubble rising thru a liquid? Expansion and an increase in velocity of the expansion.Not a perfect anaolgy, and very simplistic, I know, but a little better than the inflating balloon.If the bubble encounters an obstacle in it's trip, it will slow down and either stop, or take the path of least resistance around it towards it's "goal" of rising to the top.This obstacle will result in a temporary decrease in the rate of expansion, but the rate will increase again as it clears the obstacle.

All theories begin as "what if" or "as if" scenarios, and the details are filled in as more information is available, or the story is adjusted to fit the information. Sometimes the story requires a complete re-write, as history has repeatedly shown.

A formula or calculation is merely a stairway which we climb in order to arrive at a conclusion.It allows us to work within the limits of our intelligence to achieve a goal otherwise unattainable.In effect, they are tools, that give us mental leverage to apply to a problem.It leads us in little baby steps to a conclusion that would be self evident to a genius, who would feel no need to break it down to a Pablum state.

There have been a few of those people in history, but not many.

Bubble?Balloon?Slinky,Lambda?Sure, why not. Whatever helps you comprehend the universe in which we live is ok, regardless of the level of sophistication.Never bite off more than you can chew (or eschew).

A thousand years from now, mankind will look back and wonder:What were we thinking, and how primitive our theories, (with a possible few exceptions), and some of the scientific elite of today will be viewed as very primitive.But we must perform our role, for the future is built upon the ashes of the past, victories as well as defeats.I just hope we learn enough to survive as a species, without having to start all over again from the radioactive ashes.