Possible matter being Created/Destroyed?

[Samuel99]

Well I'm a pretty young kid. But i know a lot about physics and a special astronomy. Me and another very intelligent Friend were talking about something today. The first rule of thermodynamic states that energy can't be created nor destroyed. Matter is a type of energy but in a more compact state (I'm not Sure if I'm correct). At the edge of the universe the universe is expanding/Collapsing. If it is expanding more and more of the universe is being created out of nothing. Wouldn't this be matter being Created and if/or it were collapsing were would all the matter go therefore it would be destroyed? Also All the matter being sucked into black holes does the intense gravity destroy anything being sucked in? Thank you for all your answers. O yes i forgot I'm 12 turning 13 if any of you wanted to know.

 

[Samuel99]

Edit: I'm Really wondering so can anyone please answer ?

 

[phinds]

Welcome to the forum. I do suggest that you read the rules. IMMEDIATE bumps are not appreciated. Once after 24 hours is acceptable.

You have a misunderstanding in that there IS no "edge" to the universe so the rest of that question is meaningless.

No one really knows WHAT happens inside a black hole but for small black holes, matter is heavily distorted outside of the event horizon (look up spaghettification).

EDIT: I suggest that you read the FAQ in the Cosmology subforum. Some really useful info there and it is reliable, unlike much of what you find on the internet.

 

[Samuel99]

What I meant to say is not the edge of the universe but the point of where the universe is expanding. The point would be like the absolute farthest you can go in the universe but that point keeps getting farther and farther as it expands.

 

[HallsofIvy]

You are completely misunderstanding what "expanding universe" means. The universe is "expanding" everywhere not just at "the absolute farthest you can go". That is, the distance between the sun and proxima centauri is very, very sightly greater than it was last year, the distance between the sun and the Earth is very, very, very slightly greater (an unmeasurably small change). It is space itself that is expanding.

 

[Samuel99]

O ok thank you but i have one more question if i may ask. In the big ban theory it states that a explosion cause the universe to start expanding. If this is true then why did the universe start expanding from that one point. Wouldn't matter be created as the universe grew and grew?

 

[phinds]

O ok thank you but i have one more question if i may ask. In the big ban theory it states that a explosion cause the universe to start expanding. If this is true then why did the universe start expanding from that one point. Wouldn't matter be created as the universe grew and grew?

The Big Bang theory most emphatically does NOT say that it started at a point, in fact, it says quite the opposite ... it started EVERYWHERE. There is no center, there is no edge. There was never a "point of origin".

You need to read up on cosmology, as I have already suggested.

 

[sophiecentaur]

It is a difficult concept to deal with but Space, itself, was very 'small' at the time of the BB. At least, that's what observations imply.

 

[Samuel99]

The Big Bang theory most emphatically does NOT say that it started at a point, in fact, it says quite the opposite ... it started EVERYWHERE. There is no center, there is no edge. There was never a "point of origin".

You need to read up on cosmology, as I have already suggested.

How would it start every where? It must have started from a specific point and started growing from that point on. If I'm wrong and you are right how would it start expanding from everywhere and where is everywhere?

 

[phinds]

How would it start every where? It must have started from a specific point and started growing from that point on. If I'm wrong and you are right how would it start expanding from everywhere and where is everywhere?

HOW it did that is a good question and I'm not aware that anyone knows the answer. THAT it did that is not in serious dispute and is accepted cosmology.

Things on the very large scale (cosmology) and the very small scale (quantum mechanics) are often completely unlike what our intuition and experience tells us they should be because we do not LIVE in those scales. Read some actual science instead of thinking that your intuition/experience is worth anything in these situations.

 

[phinds]

It is a difficult concept to deal with but Space, itself, was very 'small' at the time of the BB. At least, that's what observations imply.

I think "smaller" is a better description, since it is possible that it was infinite, which of course isn't really "small".

 

[sophiecentaur]

I think "smaller" is a better description, since it is possible that it was infinite, which of course isn't really "small".

I think the word "small" is OK for a 13 yr old. "Infinite" and relative sizes of Infinity tends to bring on the pains.

 

[skeptic2]

One analogy which may be useful here is that the universe is not expanding like the volume of a balloon expands when you blow it up. Rather it is like the three dimensions of our universe are reduced to the two dimensions of the balloon's surface. As the balloon is blown up, every point recedes from every other point and there is no farthest point.

Disclaimer: This analogy fails on various levels including that we have no evidence that the universe is closed, but it should be sufficient for this discussion.

 

[mattynet1]

Your question is very important reguardless of your age. It shows you can think out of the box and think for yourself. It is a theoretical question to which there is no answer only theories. In my opinion a real conversation is needed on this topic with knowledgeable people who understand this. Understanding the problem and The Scientific Method is very important. This is how we learn and check the information we use. I will say this to you, the rules of quantum and classical objects are what this is about. You are correct it is about energy and what that is when the formula E=Mc2 is applied. Energy is how we describe matter which is everywhere under the E=Mc2 equation. In my opinion keep on doing what you are doing. Imagine in your mind what these concepts are. Think like a Einstein. This will bring you and me closer to a understanding of the truth when we collaborate and figure this out. The so called Unified Field theory.

 

[phinds]

I think the word "small" is OK for a 13 yr old. "Infinite" and relative sizes of Infinity tends to bring on the pains.

Good point.

 

[dilletante]

That is, the distance between the sun and proxima centauri is very, very sightly greater than it was last year, the distance between the sun and the Earth is very, very, very slightly greater (an unmeasurably small change). It is space itself that is expanding.

My understanding was that distances between objects in gravitationally-bound systems such as galaxies and solar systems are not increasing.

 

[phinds]

My understanding was that distances between objects in gravitationally-bound systems such as galaxies and solar systems are not increasing.

That is correct. Hallsofivy clearly does not understand the expansion.

 

[Samuel99]

One analogy which may be useful here is that the universe is not expanding like the volume of a balloon expands when you blow it up. Rather it is like the three dimensions of our universe are reduced to the two dimensions of the balloon's surface. As the balloon is blown up, every point recedes from every other point and there is no farthest point.

Disclaimer: This analogy fails on various levels including that we have no evidence that the universe is closed, but it should be sufficient for this discussion.

This is a analogy that my science teacher told me. But there is something wrong with useing a balloon being blown up as a analogy. The balloon expands because of the matter your adding into it. You are taking air from your lungs/helium from a tank and putting it inside of the balloon while nothing is adding matter to the universe. This is why i though new matter was being created.

 

[skeptic2]

It is not necessary to add matter to a balloon for it to expand. The balloon could be put in a vacuum chamber and the air in the chamber be pumped out.

The point is we don't know exactly why the universe is expanding. I think the consensus would be however that adding matter to the universe would tend to reverse the expansion.

 

[Drakkith]

How would it start every where? It must have started from a specific point and started growing from that point on. If I'm wrong and you are right how would it start expanding from everywhere and where is everywhere?

A couple of things here. First, it is our current understanding that the universe is most likely infinite in size. This is extremely hard to understand, so don't worry if it doesn't make sense at first. Second, when we look far away in the distant universe we see it as it was in the past. (Because light travels at a finite speed, not instantly) So we can view the universe as it was at various points in the past.

Our observations have told us that everything in the universe that is larger than a galaxy cluster is getting further away from everything else.(Galaxies group into clusters, which then group into Superclusters) IE our own galaxy's supercluster is getting further away from all other superclusters. We also see that the way everything is moving is apparently the result of ALL superclusters getting further away from ALL OTHER galaxy superclusters.

This effect of everything getting further away from everything else is what we call "Expansion". Take a rubber band and draw 5 dots equally spaced apart on it. Now, hold the rubber band with your thumb on the first dot and pull it with the other hand. You will notice that dot 2 is a little bit away from dot 1. BUT, dot 3 is about twice the distance from dot 1 that dot 2 is. And dot 4 is about 4 times the distance that dot 2 is, and twice the distance that dot 3 is.

Now take the rubber band, hold it with your thumbs on the end dots and pull with both hands, keeping the middle dot from moving around. From that dots point of view, the dots next to it are a little bit away, but the end dots are twice as far! This is how expansion works, except that the dots are actually galaxies. From each galaxies point of view everything else is expanding away from it.

The key here is to realize and understand that we CANNOT see the entire universe. It simply isn't possible. We can only see a small portion of it that we call the "Observable Universe". So we think that the universe is either MUCH larger than what we can see, but still finite in size, or it is infinite.

Since we see this, we can reasonably say "If the universe is expanding, then in the past everything must have been closer together". So we do our models and work backwards and eventually we come to find out that far back in the past everything in the universe seemed to be so close to everything else that the density and temperature was VERY VERY large. It gets to the point that we can't even calculate what happens because our math starts to give us infinities and nonsense. It is at this point that we say the "Big Bang happened".

My understanding was that distances between objects in gravitationally-bound systems such as galaxies and solar systems are not increasing.

This is my understanding as well.

 

[Drakkith]

This is a analogy that my science teacher told me. But there is something wrong with useing a balloon being blown up as a analogy. The balloon expands because of the matter your adding into it. You are taking air from your lungs/helium from a tank and putting it inside of the balloon while nothing is adding matter to the universe. This is why i though new matter was being created.

That is why the balloon is simply used as an analogy, not as the real model. It merely helps to understand some of the concepts. Don't take it literally.

 

[Naty1]

Hi Samuel...great questions...
Some really smart people here...[alas, not me so much!] ...so if you hang around you can learn a lot...I'll give you some brief answers and some terminology so you can search, say in Wikipedia, and read more:

At the edge of the universe the universe is expanding/Collapsing.

As noted already, there is no edge...there is no center...maybe no end either but we think there was a beginning...Here is my favorite article summary about the big bang and expansion:

http://space.mit.edu/~kcooksey/teaching/AY5/MisconceptionsabouttheBigBang_ScientificAmerican.pdf

And some notes from a discussion in these forums:

Chalnoth:

We are at the temporal edge of the universe because nothing in the observable universe is older than us relative to the BB; it also appears we are at the center of the observable universe because we can see equally 'distant' in every direction. It is obviously illogical to be both at the center and edge of any geometrical shape aside from a point. The only logical alternative is the universe has no edge or center.

Marcus: What you see in ordinary mainstream cosmology (something like 99% of the published papers) is a model of the universe as something which is spatially without boundary. [my comment: think of the surface of a sphere.]

That is, you could say, how the concept of universe is defined: spatially speaking it is the thing that has no boundary. This means that expansion can only be pictured/experienced from the inside. One experiences and measures expansion as the gradual increase of distances between stationary objects.

Since it has no boundary, space can have no "outside". So expansion cannot be pictured from the outside. This little difficulty normally trips up beginners. They are used to thinking of expansion seen from outside.

You have to learn to think of expansion seen from within, as a pattern of increasing distances---it is currently a percentage growth rate of about 1/140 percent per million years. So naturally the larger distances increase faster.

[my comment: This makes no 'sense' in our ordinary view of most things...but it is accurate!]

If it is expanding more and more of the universe is being created out of nothing. Wouldn't this be matter being Created and if/or it were collapsing were would all the matter go therefore it would be destroyed?

It's actually space and cosmological energy being created rather than matter! for energy read about 'dark energy'... For collapsing, read about the 'big crunch'...but it is currently believed the universe will go on expanding 'forever'. Otherwise, in a collapse, everything might end up in a monumentally sized black hole.

http://en.wikipedia.org/wiki/Big_crunch

Also All the matter being sucked into black holes does the intense gravity destroy anything being sucked in?

yes. All that remains is what is encoded on the surface of the event horizon...on the 'outside' It's like the 'roach motel' [a capture device]...'you can check in but you can't check out'! Nothing escapes out beyond the event horizon. Everything is crushed out of existence at the 'singularity' inside...but nobody knows exactly what that singularity really is because our mathematics breaksdown there. But we are pretty sure it will be really interesting when we find out. The other really cool 'singularity' is the one that started the big bang. Some think time started there, others think space and time popped into existence together. Just how are those alike and how are they different?? nobody knows for sure.

 

[Naty1]

My understanding was that distances between objects in gravitationally-bound systems such as galaxies and solar systems are not increasing.

That is correct. Hallsofivy clearly does not understand the expansion.

While I tend to agree that this may not be the best example, because these objects are only 4 light years distant, Hallsofivy is technically correct...for example, an observer billions of light years distant includes us in her expanding view of the universe.

I don't believe there is a calculable distance at which 'cosmological expansion' begins to overpower gravitational attraction...but we DO usually consider that to be meaningful at intergalactic distances...and inconsequential at only 4 light years...

 

[Samuel99]

Very good answers and thanks for the links.

 

[Drakkith]

While I tend to agree that this may not be the best example, because these objects are only 4 light years distant, Hallsofivy is technically correct...for example, an observer billions of light years distant includes us in her expanding view of the universe.

I don't believe there is a calculable distance at which 'cosmological expansion' begins to overpower gravitational attraction...but we DO usually consider that to be meaningful at intergalactic distances...and inconsequential at only 4 light years...

To my knowledge gravity easily dominates and the expansion is completely negated. Look at it this way. The force of expansion can be viewed as a reduction in gravitational force since it would be a force in the opposite direction. If we reduce the gravitational force of the Sun holding the Earth in orbit by about 0.0000000000001%, the Earth moves very very slightly further out on it's orbit and simply stops. There is no further increase in distance though.

 

[Naty1]

"To my knowledge gravity easily dominates and the expansion is completely negated..."
IOf you man at a distance of about 4 ly, I'd agree any 'expansion' is immeasureably tiny.

Look at it this way

By your stated logic, cosmic expansion should come to a stop?

 

[Naty1]

Samuel:

does the intense gravity destroy anything being sucked in?

as already discussed, yes...I came across a description of two theoretical ways this might happen..
Quotes are from BLACK HOLES AND TIME WARPS by Kip Thorne. [This is a great book without any math and really gets into a lot of detail about black holes.] [pg 473-475]

..When a black hole is created by an idealized spherical imploding star...Oppehheimer and Synder showed us... when nearing a singularity everything experiences an infinitely growing radial stretch and transverse squeeze...and thereby gets destroyed

This means 'tidal gravity' destroys everything as a singularity is approached.

...Belinsky, Khalatnikove and Lifgarbagez [BKL] showed random deformations in real stars will completely change the holes interior...the above description is 'unstable against small perturbations'...[the BKL solution is stable] and the BKL singularity is somewhat like a taffy pulling machine...it stretches and squeezes first in this direction, then that, then another,and yet another. The stretch and squeeze oscillate with time in a random and chaotic manner as measured by an infalling observer...this is a chaotically oscillating singularity...When the black hole is newborn, its interior tidal forces exhibit violent,chaotic BKL type oscillations. As the hole ages ...they gradually disappear...[and a tidal gravity explanation dominates]...

 

[Naty1]

Samuel posts:

Matter is a type of energy but in a more compact state (I'm not Sure if I'm correct).

Doesn't look like anyone commented..so I will. That's probably an untestable comment...compact relative to what? I like the concept and if it helps you interpret things great.

Matter does have a lot of energy as Einstein showed us [from E = mc²].
With nuclear reactions [fission and fusion] we can access a few percent of that energy. With chemical reactions, which don't affect the nucleus, even less.
I'm not positive, but I think matter-antimatter collisions produce the most energy...100% of the mass becomes energy...but that doesn't mean such mass has any more energy density or is more 'compact' than other mass...just that we can get more out...

This is a really advanced concept: "One could think of a
particle [mass] as a localized concentration of zero-point energy which gravitates and resists acceleration ... no traditional "mass" needed." [Zero point energy is the inherent energy in a vacuum...fluctuations of ground state [lowest energy but not zero] conditions due to their wavelike nature.] I checked ENERGY DENSITY here
http://en.wikipedia.org/wiki/Energy_density
and did not find anything of great interest...but they list Planck energy density as biggest,
then antimatter..then uranium...take a quick look at the charts if interested...

Under Planck Density I found this:

...This is a unit which is very large, about equivalent to 1023 solar masses squeezed into the space of a single atomic nucleus. At one unit of Planck time after the Big Bang, the mass density of the universe is thought to have been approximately one unit of Planck density...

So we probably won't be using THAT for a while!

 

[Drakkith]

"To my knowledge gravity easily dominates and the expansion is completely negated..."
IOf you man at a distance of about 4 ly, I'd agree any 'expansion' is immeasureably tiny.

Yes, I mean at distances less than multi-megaparsecs.

By your stated logic, cosmic expansion should come to a stop?

Only where objects are held together strongly enough by gravitation and the other forces.

 

[chrisbaird]

Yes, I mean at distances less than multi-megaparsecs.

Only where objects are held together strongly enough by gravitation and the other forces.

The point is that cosmic expansion itself does not stop. Space itself is everywhere expanding, even here on earth. But as the Earth is bumped slightly father away from the sun due to cosmic expansion, it does not have the velocity to sustain a higher orbit, so it returns to its original distance from the sun. Shrink this bumping/returning process to an infinitesimal moment in time, and you see that the Earth never really moves outside its regular orbit. So it's not that the distance between the Earth and the sun is increasing due to cosmic expansion, but the amount is so small to be negligible. Rather, the distance between the Earth and the sun is not increasing due to cosmic expansion, despite space itself expanding around the earth. It's like the tablecloth being pulled from underneath the cups without upsetting them.

 

[phinds]

The point is that cosmic expansion itself does not stop. Space itself is everywhere expanding, even here on earth. But as the Earth is bumped slightly father away from the sun due to cosmic expansion, it does not have the velocity to sustain a higher orbit, so it returns to its original distance from the sun. Shrink this bumping/returning process to an infinitesimal moment in time, and you see that the Earth never really moves outside its regular orbit. So it's not that the distance between the Earth and the sun is increasing due to cosmic expansion, but the amount is so small to be negligible. Rather, the distance between the Earth and the sun is not increasing due to cosmic expansion, despite space itself expanding around the earth. It's like the tablecloth being pulled from underneath the cups without upsetting them.

Are you sure about this? It has been my belief that "dark energy" EXISTS locally, but has absolutely no effect at all. Not "negligible", but ZERO.

 

[Drakkith]

The point is that cosmic expansion itself does not stop. Space itself is everywhere expanding, even here on earth. But as the Earth is bumped slightly father away from the sun due to cosmic expansion, it does not have the velocity to sustain a higher orbit, so it returns to its original distance from the sun. Shrink this bumping/returning process to an infinitesimal moment in time, and you see that the Earth never really moves outside its regular orbit. So it's not that the distance between the Earth and the sun is increasing due to cosmic expansion, but the amount is so small to be negligible. Rather, the distance between the Earth and the sun is not increasing due to cosmic expansion, despite space itself expanding around the earth. It's like the tablecloth being pulled from underneath the cups without upsetting them.

I'm not sure I see how this is any different than what I explained. The Earth isn't moving away from the Sun at all. Whether expansion simply doesn't happen, at all, within our solar system, or whether it takes place but is negligible and overpowered by gravity is beyond my ability to answer.

 

[Samuel99]

My understanding was that distances between objects in gravitationally-bound systems such as galaxies and solar systems are not increasing.

But they are increasing and we know this because of red shift. As galaxies move farther away from each other they appear to look redder in color.

 

[Naty1]

Drakkith posts:

I'm not sure I see how this is any different than what I explained.

but it is different and that's what I already posted.

chrisbaird captured what I meant in one short statement:

The point is that cosmic expansion itself does not stop.

The fact that gravitationally bound local systems may not move is not the measure of expanding space. Another way to think of it is that over billions of years, if nothing else changed, space would continue to expand but gravitationally bound local systems would not.

 

[phinds]

But they are increasing and we know this because of red shift. As galaxies move farther away from each other they appear to look redder in color.

You completely misunderstand. Try to get a grasp on "gravitationally bound systems" such as local clusters of galaxies.

Galaxies OUTSIDE gravitationally bound systems behave as you believe, but not ones inside which is what the statement was about.

 

[Ich]

Whether expansion simply doesn't happen, at all, within our solar system, or whether it takes place but is negligible and overpowered by gravity is beyond my ability to answer.

This is a purely philosophical point. Expansion in itself has no effect at all on local dynamics. The only thing you notice are the gravitational effects of local matter and energy (including DE). In an ideally homogeneous universe, these are proportional to \ddot a / a, the acceleration (or deceleration) of the expansion.

 

[Drakkith]

Couple of questions here.

1. If the distance between 2 objects is not increasing, due to normal gravitation, can you consider spacetime to be expanding between those objects?

2. Does the force of expansion cause the orbits of bound objects to be very slightly larger than they would be without expansion by opposing the forces holding them together?

 

[phinds]

Couple of questions here.

1. If the distance between 2 objects is not increasing, due to normal gravitation, can you consider spacetime to be expanding between those objects?

I don't see how you could, since it isn't

2. Does the force of expansion cause the orbits of bound objects to be very slightly larger than they would be without expansion by opposing the forces holding them together?

I don't see how that could be since if it DID happen, it would continue to increase, would it not, and then we would have evidence of it (and likely a lot of bad consequences). I mean, why would you assume that once expansion had an effect, it would just STOP having an effect?

 

[Ich]

1. If the distance between 2 objects is not increasing, due to normal gravitation, can you consider spacetime to be expanding between those objects?

Spacetime is never expanding. Space is expanding, and therefore "expansion" is just as coordinate dependent as "space". Wich means: you can consider space expanding there or not, it makes no difference.

2. Does the force of expansion cause the orbits of bound objects to be very slightly larger than they would be without expansion by opposing the forces holding them together?

There is no force of expansion.

 

[Drakkith]

Well, now I'm very confused again.

 

[Ich]

Why?

To be sure, I disagree with

I don't see how that could be since if it DID happen, it would continue to increase, would it not, and then we would have evidence of it (and likely a lot of bad consequences). I mean, why would you assume that once expansion had an effect, it would just STOP having an effect?

(wrong)

The fact that gravitationally bound local systems may not move is not the measure of expanding space. Another way to think of it is that over billions of years, if nothing else changed, space would continue to expand but gravitationally bound local systems would not.

(correct, but then: nothing is a measure of expanding space, except the things that are moving away from each other. If they aren't, well, what's the point of talking about expanding space?)

But as the Earth is bumped slightly father away from the sun due to cosmic expansion, it does not have the velocity to sustain a higher orbit, so it returns to its original distance from the sun.

(wrong)

 

[Drakkith]

Why?

Because this is a confusing topic.

 

[Ich]

Fair enough.

 

[Eimacman]

Greetings Drakkith:

I am also a little confused, perhaps I can dispel it.

The universe is expanding, this is shown by red-shift. No one can measure this directly because the instrumentality would be directly effected. Example if one tried using a ruler to measure the expansion of space the result would be nothing, being that the ruler would be "expanded" as well. This is due to the ruler being in space and being part of space.

The rate of expansion would be effected by gravitation, planets, star systems, clusters, galaxies, galaxy clusters, and so on; as well as any effects of dark-energy and dark-mater. The change of distance between Sol and Alpha Centari would increase because because of the expansion of space-time, but because of the local effects of the Milkyway's supermassive black hole, the combined gravitational effects of the stars as well as the gravitational effects of the halo of dark matter around the galaxy, would make such expansion possibly unreadable or very small.

The effects of such an expansion, if it is accelerating as current data suggests, all matter will eventually become unstable and decay into low energy photons spread across a cold universe. Matter would not have been destroyed only converted into energy, but so diffuse that it could never be used. This would be in the very very very distant future.

 

[Mark M]

No one can measure this directly because the instrumentality would be directly effected. Example if one tried using a ruler to measure the expansion of space the result would be nothing, being that the ruler would be "expanded" as well. This is due to the ruler being in space and being part of space.

Eimacman, this is incorrect. The space in between galaxies is growing, the objects within space are not.

 

[Eimacman]

Greetings Mark M:

Could you explain why an object would not be effected by the expansion of space-time, neglecting the local effects of gravitation?

 

[Mark M]

Greetings Mark M:

Could you explain why an object would not be effected by the expansion of space-time, neglecting the local effects of gravitation?

Eimacman, the expansion of space has absolutely no effect on an objects size. If it did, we wouldn't see any expansion - galaxies would simply grow with the expanding space.

 

[George Jones]

Greetings Mark M:

Could you explain why an object would not be effected by the expansion of space-time, neglecting the local effects of gravitation?

For an expansion on what Mark M said, see

http://arxiv.org/abs/gr-qc/0508052.

 

[afrinnover]

Sorry, I'm new comer, how to posting ?

 

[phinds]

This is a purely philosophical point. Expansion in itself has no effect at all on local dynamics.

I don't understand how this is a philosophical point. Either the expansion of the universe DOES have an effect on local scales or it DOES NOT have an effect. I see absolutely NOTHING about that that is philosophical.

Now, as to whether it MATTERS, I could agree that that's as much philosophical as factual since as I now understand it, if it DOES have an effect, it is negligible and will remain negligible in the solar system for the life of the sun.

Whether or not the effect would (if it exists) be negligible at a galactic scale I do not understand.