3 Oct 2006 21:41:32 UTC

Topic 191895

(moderation:

I went to 2 seminars this past weekend by a PHD astronomer Dr. Hugh Ross. (http://www.reasons.org/about/staff/ross.shtml) He was talking about the creation of the universe and the extremely fine line between an open and closed universe. He mentioned something which I never got the chance to question him on. He said:

If at any time in the past the mass of the visible universe varied by more than the mass of a dime (10 cents), then the current universe would be unrecognizable and life not possible. It would either collapse, or expand uncontrollably.

I wanted to ask him the following questions:

1) How can scientists know the mass of the visible universe so accurately to calculate what the difference the mass of a dime would make.

and

2) Isn't the mass of the universe changing all the time? Doesn't stars convert mass into energy making the universe "lighter"?

Can anyone shed light on what the Dr. said and my questions? Thanks.

Language

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## Does this make sense?

)

Unfortunately I can't shed light on anything much, but...

I'm under the impression that energy and mass are equivalent (from E=Mc^2), and so energy has mass (weight?)

I'm thinking: if we have an indestructible hollow sphere containing some mass, this sphere would have a certain weight (whatever weight might mean), and if we were to somehow convert all that mass inside the sphere to energy, and assuming that the indestructible sphere is a super insulator (or something like that) so that no energy/radiation can escape, then the sphere and it's contents will weigh exactly the same as it did before.

Therefore, even though the mass inside the sphere is being converted into energy, the sphere is not actually getting any lighter.

I'm sure I've made a lot of gross errors, but I don't know what they are and it seems to make some kind of sense to my fevered imagination...

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## RE: I went to 2 seminars

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Well, its actually clever/sloppy use of language. What he has said is nearly true but it is more exact to say 'If at a time in the past', rather than 'If at any time in the past' ( my change/emphasis ). You see the inflationary theory incorporates a brief period of time ( after the 'Bang' but before 'normal' expansion ) in the very early universe when the size of the universe increased exponentially. This is a mathematical statement.

The properties of the exponential function are such that if I wind back in time to some prior moment then I can reach a point where a given difference in some property ( that I choose ) will be significant for subsequent evolution if changed. So if you choose a dime's worth of mass then I, using the properties of the exponential function, can find that earlier moment when it would of mattered.

However we can extend this game to any mass you like. Suppose you choose a flea's whisker of mass, then I'll just go back a bit earlier to find the time when that would have made the difference, if altered, to subsequent events. If you chose a few planets' worth of mass then I can go back, but not as far, in time to when that would have mattered. We could go up/down in our selected mass and gone backward/forward accordingly - just sliding back and forth along the exponential curve to suit.

So he hasn't weighed the universe to within a few grams, it's just that inflationary theory ( by it's construction ) has that property of sensitive dependence on some earlier condition. It's a sort of 'just so' story which leads into the anthropic stuff which I've never been excited by. We don't have an ensemble of universes to actually compare amongst and we can't rewind the tape, fiddle, and fast forward this one either ..... :-)

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

## I understand what you're

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I understand what you're saying Mike, but have scientists calculated how far back we must go in time for the mass of a dime to make a difference? Maybe if we add a galaxy we only need to go back 5B years, but to add a dime we need to go back 100B years - which doesn't make sense when comparing to the age of the universe. Hang on... I guess the exponential curve you mentioned would take care of this and always come up with a result greater than T=0?

So then basically an infinitely small change of mass at an infinitely small time period after T=0 would have made this universe unrecognizable today?

Now I know why you said this leads into the "anthropic stuff".

## RE: I'm under the

)

This is what I originally thought, but I couldn't convince myself that energy has mass. I looked at it this way...

When burning a 10kg log you end up with:

Ashes, smoke, light energy, noise energy, heat energy.

The ashes and smoke have mass. Maybe so does the light energy (not sure). But how can noise and heat have mass? They're just vibrating particles. So my understanding is except for the 3kgs or so of ashes and smoke (and light?), the other 7kgs of wood were converted to massless energy. Once the noise fades, and the heat disperses you're left with a slightly noisier, slightly warmer universe that "weighs" 7kg lighter. The total energy of 10kg is still there, but most of it is in a massless form.

Does the above make sense?

## RE: I understand what

)

Hmmmmm ......

Cosmology prior to the addition of 'inflation' theory had the issue ( amongst others ) of needing to be have pretty exact initial conditions ( at time 'zero' ) such that progression with time, the 'Bang', would lead to today's universe. Hawking and others looked at alternative scenarios of different initial states and found that uniformity in certain parameters would be required to an extra-ordinary degree ( to 1 part in a much larger number with powers of ten to many, many zeroes ) for that evolution to yield even universes vaguely similiar to ours.

This was a discomfort ....

It was found that if you kick in an exponential expansion ( inflation ) earlier on then alot important stuff ( like total energy density ) 'flatten' out to 'reasonable' values for a universe that contains us. This is the anthropic wedge. So a whole raft of alternative outcomes, many pretty radical or unimaginable, get nailed by this process.

However this puts a 'veil' on matters, as now a vast manifold of choices of starting circumstances are currently indistinguishable - and the theory of inflation guarantees this by it's design. We will never know the pre-inflation state, because inflation wiped out any imprint. So if I have some early universal state which would have, because of a dime's worth, otherwise flown off into some horrible place ( without us ) - I can simply veto that by firing up inflation at some appropriate time ( the exact moment depends on what level of variance I want to suppress ).

My cynicism is in that the declaration of

- some exact initial conditions + a 'normal bang' evolution

has been replaced by

- any old initial conditions + a process that makes initial conditions pretty irrelevant + a 'normal bang' evolution

Have we not simply 'dereferenced' our complexity here? And when will we ever have a test/control on this?

Cheers, Mike.

( edit ) I forgot to emphasize .... I'll never know exactly what the right time was for that dimes worth to be supressed by inflation because of the veil that inflation brings!! Ditto for any other 'whatever's-worth' - all I can fairly confidently say is that it wont be the same time as the dime ....... sigh

( edit ) And I think I've been guilty of sloppy language myself in this thread. I'd point out that an exponential rate of increase in the size of the universe can lead to an exponential decrease in other things that depend on some inverse power of that size. Hence the flattening or supression. For those of you more familiar with maths, I'll point out that if you have some power law - that is some_variable to some_fixed_power then I'll always beat it with an exponential. Exponential always beats a polynomial ( eventually ) - which is why the power series expansion of an exponential is an infinite sum of polynomial terms. This is why exponential change is a real 'transformer'.

Tis my bedtime now ..... :-(

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

## Can anyone comment on my

)

Can anyone comment on my "burning log" example? I'm wondering if I'm on the right track here, or way off base.

## RE: Can anyone comment on

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You're fine!

The neat thing about energy is that you can never lose it. But it changes form and there are quite a few of those.

The really neat thing is that energy is sort of 'designed' to be that way. It's a derived quantity, meaning that you have to calculate it from some other more direct thing like a time or a distance measurement(s). The Conservation of Energy is an incredibly useful principle, neatly unifying and bridging alot of otherwise apparently disparate stuff(s). But the secret is that forms of energy are defined in such a way to make that idea be true. In any new area of physics, new forces, new phenomena etc ....... new energies arise. It's basically due to one particular way of defining energy :

work = force * distance

So as something goes from A to B ( a distance ) under a force influence then energy has been exchanged in some manner. ( This can be expressed more precisely as an integral along a path ).

In fact Einstein never wrote E = m*c^2 ( in the published sense ). He was discussing the momentum of light and the reaction of a material body upon the emission of a photon and concluded that said body had lost an amount of mass = E/(c^2). Couple that in with the Special and General Relativistics corrections to dynamics ( masses varying with velocity for instance, or a gravity well robbing a photon of frequency due to time distortion ) and it all comes out in the wash.

It's not that energy conservation is a cheat in any way. It is real - try telling the people of Hiroshima/Nagasaki that it's 'just derived'. Other good conservatives are momemtum, angular momentum, charge, some ( combinations of ) symmetries ......

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

## Thanks Mike. Are there any

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Thanks Mike.

Are there any examples of converting energy into matter? Or are we slowly running out of matter and eventually this universe will be 100% energy with zero mass?

## RE: Thanks Mike. Are there

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You have to be careful with your terms, as Mike as pointed out (and given us an example to boot!) - too many folk like to toss round 'pure energy', as if it means anything - but pair production is as good an example of 'energy into matter' as any. A gamma ray photon, with enough energy, collides with something (what? it doesn't matter for the telling of this story), and an electron and positron go shooting off (or, if higher energy, pion + anti-pion, or proton + anti-proton, ...).

At a much grander scale, there are many nuclear reactions at the heart of a very massive star which has a lot of 'iron' at its core, which are 'endothermic' (they consume energy, vs 'exothermic' reactions, the kind which power most stars most of the time) ... the net is that iron nuclei get turned (back) into helium, via an infusion of energy. The result? Core collapse, which leads to a Type II supernova.

(Mike will, no doubt, jump in and tidy up the sloppiness of the above ... one should be pedantic about this stuff - too easy to misunderstand - so the details really do matter).

## RE: You have to be careful

)

You're fine, but I'll just add a few points.

The language issue is really that of the technical definition(s) versus everday term(s). Same word(s) with several materially distinct meanings, the old syntax vs. semantics problem. As long as you get the idea that energy ( like others ) is a property of something: the energy of a photon, energy of my car, energy of the supernovae explosion, energy of a pion - rather than an isolated thing. Pick a scale for magnitudes, a standard lump, and a zero level to offset from and away you go....

Certainly production/destruction of pairs of particles/antiparticles is a good example. You might want to look up Feynman diagrams, which are essentially accounting charts for particle interactions.

As for nuclear transformations, it's worth while considering nuclear binding energy. This is how much energy gets released ( in some form ) when a specified set of separated protons and neutrons are combined to from some nuclide species. ( Alternatively how much energy to put into a given nuclear species to spread its' component nucleons - protons and neutrons - to infinite separation ). Think of it like the energy cost of nuclear real estate. If you plot the nuclear binding energy per nucleon for the known nuclear arrangements then the Iron group are at the bottom of a valley. The lighter elements have less binding, as do the heavier ones. Thus fusion/combination of lighter elements runs 'downhill' to Iron, and fission/division the heavier types does to. You are right to say 'Iron' because there are a number of adjacent nuclear types real close in value here - from memory it's a Nickel one which hit's the sweet spot:

Err .... flip the vertical axis to get the 'valley'. :-)

Anyhows fusion can continue beyond Iron but you have to put in energy from some other process. A good thing too, as if we have an early universe with only Hydrogen and Helium ( and a tad of slightly heavier stuff ) then those early stars cook the gear up until Iron, then by Supernovae'ing create some of the really heavy elements. Our Sun is 'second generation' in that it formed from leftover material from the debris of early ones. Alas a star cannot simultaneously fuse beyond 'Iron' AND stay hot enough in it's core to remain upright against gravity - it collapses. There are a number of scenarios here.

One thing that we will run out of is pretty clear - usable energy. Disorder will inexorably increase to the extent that one bit of the universe will look pretty much like any other. There will not be any gradients ( hot spots separated from cold spots ) to extract work from. Entropy death.... aargh :-)

Cheers, Mike.

(edit) Finally got the image link right. FileLodge does a much better job than ImageCabin!

(edit) Let's try ImageShack.... yep, nicely done!

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal