Horizon Tonight even more confused

[Astro_Baby]

Only gravity ? I'd say our incomplete understanding of pretty much everything .

[Catanonia]

My theory goes as follows.

The expansion was due to the vacuum energy (dark energy). It caused the inflation to the point that matter sublimed out and slowed it down.

Dark energy and dark matter are the same thing and are the soup of the multiuniverse the causes the dark flow, or gravitational flow to other parts of the multi universe.

[661-pete]

is our incomplete understanding of gravity.

That may be the nub of it. If we don't understand everything there is about gravity, could not some as-yet undiscovered nuances in the model explain all the things currently accounted for under 'expansion', 'dark energy', and 'dark flow'?

Gravity is, I suppose, pretty reliable and well accounted for at the terrestrial scale. After all, I know full well that if I hold out this pen in front of me and let go, it will fall to the floor with an acceleration of 9.81m/s². No arguments. That aspect of gravity is easy to test. But on the cosmological scale?

[vlebo]

It was not that long ago we thought our galaxy was the entire universe , so really , we have come a long way in a relatively short time. As with all learning we need to be patient and the answers will come eventually , probably not in our lifetimes , but they will come.

[Rusty Strings]

So, could it be that our understanding of a vacuum is wrong, the vacuum is the dark matter/energy?

[Astro_Baby]

After all, I know full well that if I hold out this pen in front of me and let go, it will fall to the floor with an acceleration of 9.81m/s². No arguments.

Ahhh but on a science program on R4 recently there was an interesting small article about people studying rain and they had found that not all raindrops do fall at the supposed common rate. Typically they didn't know why but is was speculated that we may not understand gravity as well as we thought.

[George Jones]

Ahhh but on a science program on R4 recently there was an interesting small article about people studying rain and they had found that not all raindrops do fall at the supposed common rate. Typically they didn't know why but is was speculated that we may not understand gravity as well as we thought.

I doubt very much that these results raise questions about our general theories of gravity, or even that the scientists involved think that the results do. After reading your post, I wondered if this indicated a poor understanding of the particular gravity of the Earth because of a poor understanding of the non-uniformities of the Earth, not because of a poor understanding of theories of gravity.

After googling, however, I found

'Super-terminal' raindrops break speed limit - physics-math - 15 May 2009 - New Scientist

which raises questions about our understanding of raindrops, and of the interaction of raindrops with the atmosphere.

[George Jones]

So, could it be that our understanding of a vacuum is wrong

Yes, many physicists think our understanding of quantum aspects of the vacuum is poor.

the vacuum is the dark matter/energy?

The standard view is that vacuum energy might be the dark energy that drives the apparently accelerating expansion of the universe, and that this is not related to dark matter.

[mdstuart]

I suspect God is standing at the edge laughing at us???

Mark

[RikM]

What gets me is that if we look at a galaxy 20 million light years away and we are seeing as it was 20 million years ago, we could predict where it is 'now', but we have no way of knowing if it actually 'is' there, so does it really matter?

Rik

[Astro_Baby]

I dont doubt your right Mark. I think its a kind of naivete to believe we could ever understand all the issues. The more I read about science these days the less enamoured I am with it. I think it was summed up so well by SPM "we dont know what we dont know"

[Doc]

What gets me is that if we look at a galaxy 20 million light years away and we are seeing as it was 20 million years ago, we could predict where it is 'now', but we have no way of knowing if it actually 'is' there, so does it really matter?

Rik

We would know exactly where the galaxy is. Galaxies do not just change course so we can measure the speed it is travelling at say for example 200 KM/sec and then we can tell how far it has travelled or how for it will reavel.

[Macavity]

...which raises questions about our understanding of raindrops, and of the interaction of raindrops with the atmosphere.

I thought it was going to be something to do with this:

SpringerLink - Book Chapter

But, as an aside, I remember coming across (water) "Boules" - Charged droplets floating on other fluids etc., years ago now in Scientific American. Or was that during the washing up...

To return somewhat to topic: I get the impression that BEFORE galaxies, there were stars existing randomly in space? I sense some theories suggest that galaxies are actually seeded by black holes? These questions and more...

[AstroTiger]

Physicists do i think like to sit in their ivory towers looking down on other scientists justifying their position by inventing crazy theories no one can understand. As an ex chemist my mind is lost looking at these.

However ideas like Dark Matter, do to me, make a little sense if i ignore the chemist in me. As a chemist the idea that material not in ther periodic table exists is sublime and crazy to say the least.

However after reading books by Cox and indeed watching his programs it does make a lot of senses. Perhaps the invisible sandwich which holds the filling together.

I have not yet seen that horizon but i will aim to this weekend sometime.

[FraserClarke]

Physicists do i think like to sit in their ivory towers looking down on other scientists justifying their position by inventing crazy theories no one can understand. As an ex chemist my mind is lost looking at these.

I think that is a bit harsh. Physics seeks to explain the world in the most basic form it can. Unfortunately, that basic form is often very heavy in mathematics, and so far removed from the scales (of time and size and mass and energy) that we are used to dealing with, that there often simply isn't a 'simple explanation'.

A few people may obfuscate their theories to make themselves sound important -- but that is not the standard mode of operation for professional physicists. Just think, you *want* people to understand your ideas; because if they don't, they probably won't give you a job!!

I haven't seen the Horizon episode either, so won't comment on it.

[Macavity]

I think that is a bit harsh.

Heheh - Just the phrase I was going to use.

I think one should remember too that [Particle] Physics is a VERY wide ranging discipline. For every e.g. "Brian Cox", there are many RAs, Research Fellows, Grad students, Technicians, University Staff, STFC staff etc. BUILDING the experiments at CERN. Not to mention the numbers into detector R&D, design and build of electronics, programming online control and monitoring, offline analysis, Monte-Carlo simulation etc.

At least some of the "theorising" is done by these folks, in their notional "spare time"

I think too, qualifications apart, scientists are (sometimes!) quite normal? In that some may show the pathologies of the AVERAGE workplace: intellectual snobbery, laziness etc. But on the whole I'd suggest they have above average collaboration skills - Even modesty? Definitely more tolerance to others, than the pantomine villains of "The Apprentice", "Dragons Den", "Masterchef" etc.

[AstroTiger]

From a personal point of view, I don't like inflation, dark matter or dark energy. They just feel like fudges, bolt-ons to plug the gaps between maths and observation. I don't really understand all the physics but a common theme, and perhaps better explanation, is our incomplete understanding of gravity.

The thing is, i got the impression that much of cosmology had been smudged. The term "dark" being used to describe what in fact we don't know.

Its the first too that i had heard of dark flow.

Plus i dont like the bibical cop out that at the very beginning there was nothing. Matter must have come from something?

[nbrus]

... I don't like the biblical cop out that at the very beginning there was nothing. Matter must have come from something?

I don't like that either ... I think what they really mean is that nothing of what we have today existed at that point ... something else existed (energy?) and in that instant exploded and over time formed everything we see today ...

[AstroTiger]

Its where the idea for dark matter comes from too?

for example

The outer planets of our solar system as you might expect take longer to orbit the sun than the inner planets.

BUT the out stars of a galaxy orbit the galactic centre at the same rate as the inner stars? did i get that right?

i can understand if gravity is not strong enough to hold galaxies together meaning dark matter is needed. but the thing i find totally crazy is how comes none of it is here on earth?

Nothing in meteors.

Oh and it does not contain any of the 24 fundamental particles (but the mirrored 24 might!?)

I am a tad baffled i think lol

[FraserClarke]

Its where the idea for dark matter comes from too?

for example

The outer planets of our solar system as you might expect take longer to orbit the sun than the inner planets.

BUT the out stars of a galaxy orbit the galactic centre at the same rate as the inner stars? did i get that right?

Sort of. If you look at the rotation curves of galaxies, the inner parts (~5-10 kiloparsecs, say) behave exactly as you'd expect if the vast majority of matter were in stars and gas (things you can see) -- rotation velocity increases with radius. However, beyond that, the rotation velocities should start tailing off (as they do in the solar system, where 99% of the mass in the middle) -- but we observe that they don't. They stay pretty much constant. To do that with Newtonian gravity (you don't need to worry about GR at these scales), you need to have a lot of mass in a roughly spherical shape around the galaxy (you can demonstrate it fairly straightforwardly if you're handy with maths -- but I'm not!).

So, the way the stars move tells us there needs to be a big halo of mass around the galaxy. But -- there is no matter there that we can see (stars & gas). Hence, this matter is called 'dark matter' -- simply because we can detect it's gravitational effect (so it has mass, and is matter), but we can't see it ('cos it's dark).

There are several candidates for dark matter, from very low mass stars (brown dwarfs), to very cool white dwarfs (so cool we can't see them), down to exotic new types of matter. The latter seems to be the forerunner now, because we've tested for 'big' lumps of dark matter (like brown dwarfs), and can't see them. The reason we can't detect dark matter particles is that they don't interact very strongly with normal matter particles (other than with gravity). So, there are lots in the vicinity of the Earth -- but they just stream right through it (and our detectors) without leaving a trace.

The other option is that Newtonian gravity works differently on the large scale of things like gravity; but that theory has several other problems and isn't really favoured.

So - that's why dark matter is called dark matter. Then, when these funny things unexpected effects like 'dark energy' came along, they just kept the 'dark' pre-fix.

'dark flow' is, I think, pretty much tinkering at the edges. The evidence for it is not very strong. Maybe it will get stronger with more experiments, but there is probably also a good chance it will go away...

(You may have picked up that Astronomers are pretty simple when it comes to naming; Dark Matter, Black Hole, Very Large Telescope, etc.... )

[lostinspace]

Steven hawkings suggested that the speed the universe is expanding at could in theory escape the pull of gravity that threatens the universe with the "big crunch"

Anything more complicated than that hurts my head. it seems when thinking about these things you have to hold so much other info in your head at one time i feel id need a super computer to work anything out!

I live with deep respect for anyone who can understand this universe and explain a little to us as they go.

till its all worked out i will satisfy myself with amiring its beauty, interesting thread,

john

[ollypenrice]

One thing I have (shamefacedly) never really understood: At what level does the "expansion of the universe" occur?

My understanding is that it does not apply within gravitationally bound systems. The expansion is, in cosmological terms, not very rapid. On a local scale it is overcome easily by gravitational attraction so something the size of a galaxy, held together by gravity, does not expand. However, the more 'empty-ish' space you have, the more expansion you have. The accumulated expansion is not constrained by the speed of light because nothing is 'moving' in the normal sense.

TV documentaries in general? (I didn't see this one.) I watch hardly any TV and used to watch even less. Thus there is usually a considerable void between watchings and the expansion of TV documenary silliness is easy to see when a year or two separates each watching. My observations are;

- TV considers itself a visual medium and is, therefore, terrified of talking heads. The heads have to do something. Turn suddenly to face cameras in odd places. Be seen in bizarre backdrops. Be limited to ten seconds at a time. Unfortunately some of us are sufficiently grown up to like watching an expert talk, but it is assumed that audiences have Attention Deficit Disorder.

- The steady progress of science, one step forward - maybe - no - back again - try this direction - is, in TV terms, boring. What they want is THIS scenario; 'Dull witted conventional scientists have believed for years that (insert whatever. The dinosaurs died out 70 million years ago, The Egyptians bulit the pyramids, etc) but now ONE MAN - we happen to have him here in the studio - has DARED TO CHALLENGE the festering fuddy duddies of academia with A NEW THEORY (insert hackneyed old hypothesis generally rejected over the last twenty years by the professionals...)

People used to say to me, 'You missed a good documentary last night' to which I would reply, 'You missed a good book.'

Olly (Grumpy old gimmer.)

[Beulah]

Great post, Olly. Haven't watched TV for years, it has been so long now I have forgetten.

When I did have the opportunity to watch a small part of a "space" documentary a member of my family was watching, I just had the residual feeling of being force fed a McDonalds McFlurry...