can anyone explain inflation ???

[neilmr]

HI All

we are told that soon after the big bang the "expansion" of the universe was faster than the speed of light, HOW CAN THIS BE if we are now told that nothing is faster than the speed of light.

Neil

[beamish]

I'll jump in

It was the gaps/voids/space between the matter that inflated faster than light, not the matter .

In a tiny nutshell, off the top of my head from what I can remember-and all I'd dare say on a forum renowned for it's experts

[GazOC]

Thats my understanding too. Nothing actually "moved" faster than light, just the space between the matter expanded.

[Paliadon]

My turn. lol. As far as I am aware, the "bow wave" or shock from the explosion (now referred to s Dark Matter) was and is still an unknown entity. It is this that they refer to being faster than the speed of light. This would only be because the massive gravitational forces at play would have been so massive that light would not have been able to escape it at that stage, now we are only talking 1x10^-100000 or something similar, then light would have escaped in the first few molecules. Photons and electrons being the first "out" following the dark matter or course.

That is my take on it, very, very quick, but that is my interpretation.

If only we could build a 'scope big and powerful enough to be able to see the events take place, now that would be something.

Kris

[acey]

I'll have a go too.

Relativity says that information cannot travel faster than light. It doesn't actually say "nothing can go faster than light". For example, imagine a searchlight beam shining into space (and going on forever). If you move the searchlight a little bit, the beam will sweep very fast across a distant object - in fact it could sweep faster than the speed of light. But the beam isn't sending information from one part of the object to the other, so all is well.

In the case of inflation (or cosmological expansion in general) think of a kid's climbing frame - the sort with a cubical construction of metal bars. This is our "co-ordinate system", and everything in the universe can have its position measured relative to this system. For example, our Local Group of galaxies is at one junction of bars, and the Virgo Cluster is at another. Then you wait a bit and you find that the climbing frame has grown, the galaxy clusters are further apart. They haven't actually moved, it's just that the space between them got bigger - exactly as GazOC says.

In reality there are no metal bars but there is a co-ordinate system. It's not an "absolute rest frame" (something else that's forbidden by relativity), but it's a stable way of measuring the positions of things over time (possible because the universe is assumed "homogeneous", "isotropic", etc). And when you use this co-ordinate system to measure positions during the first squillionth of a second (the era of inflation) you find that things are moving apart "faster than light" - even though, relative to the co-ordinate system itself - they needn't be moving at all.

There's no "bow wave", nor can you identify some particular point where everything exploded from (if you rewind things and imagine our infinite climbing frame shrinking then it will suddenly go from being infinite to being non-existent everywhere). Nor is there any explanation for why the frame suddenly appeared out of nowhere - various models offer possible reasons (eternal inflation, branes, ekpyrotic universe etc etc).

As for explaining inflation itself, it's because relativity tells us that gravity has two sources: one is mass (or energy), and the other (surprisingly) is pressure. Inflation posits the presence of certain particles in the very early universe that gave rise to a certain kind of pressure (negative pressure!) that got the whole thing going. This sounds crazy because a balloon with negative pressure would collapse on itself, not expand - but that's because it's surrounded by positive pressure. If the whole universe is at equal (negative) pressure then you don't get any movement caused. But the pressure has a gravitational effect, and this is what drove inflation.

Andrew

[calibos]

Imagine the 3d universe as the 2d surface of a balloon. Mark dots all over the balloon to represent Galaxies. Now blow the balloon up. All the Galaxies are moving away from every other galaxy at what would be at the balloon scale much much faster than the speed of light. This is why every galaxy looks like it is receeding from us like as if earth was the center of the universe and the location of the big bang and this is why it is thought that the furthest galaxies in the universe are 40 billion lightyears away despite the fact that the universe is only 14 billion years old. Inflation of the balloon/universe is what makes it seem like those 40billion LY away galaxies must have traveled away from us at 3 times the speed of light

[gls]

I honestly don't understand inflation theory, saying it's the space between the galaxies that's moving and not the galaxies just doesn't make sense to me. Surely the fact that the furthest galaxies are where they are proves that, if the big bang theory is correct, they moved quicker than the speed of light. If they didn't they wouldn't be there.

If I was stopped by the police for speeding and said "I wasn't speeding, the space between us was expanding" they'd laugh at me, and rightly so, so why is it different with galaxies?

As you can probably tell I'm quite new to all of this.

[dark knight]

Surely the space in between (dark matter) is pushing things further apart, a bit like a wave carrying a ball further from shore. Branes ripples.

[acey]

Inflation is not the same thing as cosmological expansion - inflation is a particularly rapid kind of expansion believed to have taken place just after the Big Bang. The universe at present is expanding but not inflating, in the technical sense.

All speeds are relative, we know that from Einstein. If you're caught speeding then you've gone too fast relative to a speed camera (and relative to the Earth's surface). Two galaxies can have an apparent speed relative to each other (measured by red-shift) but they can also have a speed relative to the universe as a whole, and this speed can be zero for both of them.

How do you measure your speed relative to the universe? You look at the microwave background radiation. If it appears to be exactly the same temperature in every direction then you're at rest relative to the "Hubble flow". If it looks a bit warmer ("bluer") in one direction and cooler ("redder") in the opposite direction, then you have some motion relative to the flow. Our Earth/solar system/galaxy exhibit such motions, which have to be factored out in studies of the microwave background.

So let's suppose we've got two spaceships in different parts of the universe. Both of them are measuring a perfectly uniform background radiation and both of them see a red-shift of radiation from the other spaceship. We can say they're both stationary while space expands between them.

Andrew

[gls]

Surely the space in between (dark matter) is pushing things further apart, a bit like a wave carrying a ball further from shore. Branes ripples.

I thought dark matter was the hypothetical substance that holds galaxies together, not pushes them apart.

I understand the allegories (waves pushing balls, raisins expanding in a cake etc.) it's the rest of the theory I have big problems with. What I don't understand is how, on the one hand, they can claim that nothing can travel faster than light but on the other say that the universe is over 90billion light years across and only 14billion years old. Saying it's the nothing in between that's expanding just doesn't make any sense to me. I would've thought that the very fact that the objects are where they are proves that either a) they can travel faster than light the universe is older than we think or c) that the big bang theory is simply wrong.

What do I know though? I'm just a layman.

All speeds are relative, we know that from Einstein.

As I understand it time is relative (spend an hour with a pretty girl etc.) and speed is simply whatever distance an object has travelled divided by whatever time frame you're using. So if Einstein was correct when he said that the speed of light is constant (in a vacuum) and that nothing can accelerate faster than the speed of light (due to it needing an infinite energy source) it should be fairly safe to use light as the benchmark.

[themos]

I suggest you forget about "nothing travels faster than light". It confuses people. You can, though, think "nothing travels faster than light, RIGHT HERE, RIGHT NOW". Distant objects, in space and time, can appear to do all kinds of strange things.

[themos]

Saying it's the nothing in between that's expanding just doesn't make any sense to me.

Take a pound coin out of your pocket. It is the same pound coin that was around 10 years ago. And yet it's worth less now than then. The local aspect of it has not changed, but the relations it has with other objects (a pint of beer, say) has. You used to need 2 pounds for a drink, now you need more. Same with the universe. You needed 3 billion light years to separate galaxy A and galaxy B way back then. Now you need 4 billion light years.

[buddyarrows]

May be the speed of light was faster then !!!! After all it took Astronomers 50 years to accept that the speed of light was 186,000 mps and not infinite! We are always amazed at how wrong we where before we know better.

Just tryin with my 2p worth.

Regards and clear skies

David

[themos]

There is research into theories with variable speed of light ([astro-ph/9811018] A time varying speed of light as a solution to cosmological puzzles) so it's not as if people have a closed mind about it.

The thing about this changing of the length scale with time is that it falls naturally and easily from the Einstein equations applied to the whole universe, imagined as featureless as possible. And you don't need to vary the speed of light for it.

[brianb]

we are told that soon after the big bang the "expansion" of the universe was faster than the speed of light, HOW CAN THIS BE if we are now told that nothing is faster than the speed of light.

All this (supposedly) happened in a very very short period after the "Big Bang" when the universe expanded from the Plank dimension (~10^-35 m) to the size of a grapefruit (~0.1m). During this expansion the laws of physics were not the same as they are now, there was only one force rather than the four we are familiar with ("strong" and "weak" nuclear forces, electromagnetism & gravity) and it really doesn't help to think in terms of "the speed of light" as there was no light!

It makes more sense to think of four of the 10 or 11 dimensions envisaged by "string theory" suddenlty unravelling and becoming the four dimensional space-time we're accustomed to.

But inflation itself is a "kludge", really it can't be experimented on, it's just a convenient explanation as to why the universe is as lumpy as we find it. Maybe one day we'll have a better explanation.

[dark knight]

There are also other factors involved. Time actually slows as we approach the speed of light or so I was informed watching The Universe last night. I've stopped trying to understand it as it's just beyond my comprehension (a bit like women and numerous other things).

[themos]

Time actually slows as we approach the speed of light or so I was informed watching The Universe last night.

Time, for the traveller, is not affected by speed. You won't experience anything funny if you get accelerated slowly, continuously, for 10 years. You'll get a surprise when you try to go back, though.

[michaelmorris]

For what it's worth, here is my understanding of the 'Nothing travels faster than light, but it does' debate. The point is that nothing moves faster through space than light. The space through which the light is travelling can expand at any rate.

The result of all this is that inflation is theoretically possible and that at it's further points from us, space is expanding so fast that the light leaving it will never reach us because the space between us and the star is expanding greater than the speed of light. The minimum distance from us at which this happens defines the limits of the observable universe.

IMHO the whole inflation business sounds very much like a fudge to me; a mathematical construct to overcome discrepencies between theory and observations. I have a hunch inflation will one day be shown to be balony. The variable speed of light explanation sound much more elegant a solution to me (a biologist but not a physicist!).

[dark knight]

I agree with you Michael, we have an inbuilt urge to explain everything and when we can't, we can only theorise by using mathematics. How do we know the theories we use on earth are applicable in space?? It is only when we travel further and spend more time in space that we will learn whether all these theories are correct.

carl

[themos]

we have an inbuilt urge to explain everything and when we can't, we can only theorise by using mathematics.

That constraint is fruitful, though. It enables other clever people to make experiments and say, no, it CAN'T be like that or yes, that model also predicts these observations.

[acey]

Regarding variable light theories, remember that it makes no real sense to say that the speed of light alone has changed over time, because there is no other standard of speed against which to measure it.

The variable light speed theories instead involve the change over time of dimensionless quantities (such as the fine structure constant) which involve the speed of light as well as other quantities (electron charge etc). Light speed changes, but so do the other quantities, such that their dimensionless combination (a bare number) can be charted over time.

A few years ago there was a study suggesting a change had possibly been observed in the fine-structure constant (through observations of distant galaxies), but I haven't heard any more about that. Inflation is still the favoured option though that doesn't of course mean it's right.

"Going into space" won't give us the answer.

You don't need to go into space to know the Earth is spherical.

Andrew

[dark knight]

Aha, but were not questioning whether the earth is spherical. there is nothing to suggest the conditions that exist in our galaxy are the same as others and therefore to try to explain all with theories that may or may not be applicable is only based on presumption. Presumption is a dangerous path to follow.

[themos]

there is nothing to suggest the conditions that exist in our galaxy are the same as others

But there is: spectra, supernovae, orbital profiles.

[dark knight]

Sorry Themos et al, as soon as I posted that I knew I was leaving myself wide open lol. What I should have said was....hmm maybe not, I'll only end up wide open again.

[themos]

I know what you're saying though. I think dark matter evidence comes from other galaxies, I don't think there is any local evidence for it.