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Old Oct 9th 2013, 09:51 AM   #1
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Plasma and Gravity

Thanks for your kind and prompt reply. Moreover, explanatory. In regard to the sea of photons, I don’t know what I was thinking: perhaps that’s how I am when tired: stupid (and I’m so tired right now).

There is something else I don’t understand: is (cosmic) plasma affected by gravity in any way?

I mean, 99% of (normal) matter is plasma, and yet we claim a gravitational universe. Why is that? On the other hand, how can we be certain that a celestial body’s orbit is not affected by electromagnetism in any amount? And if it is affected, how can we determine the amount (the rest being gravity)?

And upon reading your previous answer, I also thought of this: why is the night black (Olbers’ paradox)? Each and every time we put a more advanced equipment in the direction where we could previously only see black, we now see a source of light. Depending on 2 factors: how new they are (technological advancement) and how long we keep them pointing there. So, again, why doesn’t the night sky blind us? Cosmic expansion would delay the moment of discovery (and also remove some light sources from ever being discovered by us - the cosmic horizon), but new discoveries will eventually happen, I think.

Many thanks.
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Old Oct 9th 2013, 10:22 AM   #2
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Plasma is ionized matter - the positively-charged nucleii of hydrogen and helium atoms, for example - so plasma has mass just as hydrogen atoms have mass. And consequently plasma is affected by gravity.

As for whether the electromagnetic charge of plasma streaming through space can effect the orbit of a planet - not unless the planet has a charge. However one can imagine that the impact of plasma on the surface of a planet facing the plasma source (such as the sun) would cause a tiny repulsive force - probably too small to be measurable on an object as massive as a planet. But in theory you could put tis force to use - consider a small space ship with a very large "sail" that could be propelled by the impact of plasma from the sun. This type of ship has been proposed as a cheap form of propulsion for traveling to outer planets.

You seem to be familiar with Olber's paradox. There are several possible explanations for it:

A. The universe is not infinite in size, so consequently there are only a finite number of stars out there that can contribute light to the brightness of the night sky.
B. The universe is not infinitely old, so even if it is infinite in size and has an infinite number of stars there hasn't been an infinite amount of time for the light from all those stars to reach us, or
C. The energy of photons from very old and distant stars is reduced by red shift.

Any one of these, or several in combination, can explain Olber's Paradox. Modern cosmologists believe in all three.

Last edited by ChipB; Oct 9th 2013 at 10:30 AM.
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Old Oct 9th 2013, 11:50 AM   #3
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If plasma has mass and is therefore affected by gravity, it also means it provides its own gravity. So I suppose the question remains: how much of the gravity Mars ‘feels’ is from the Sun and how much from plasma? Remember that 99% of the (normal) matter is plasma. At this point I don’t think the Newtonian view is accurate. Neither is Einstein. That or somehow all the plasma in the solar system has no gravitational effect whatsoever – but then we would have to explain why.

As for the charge of a planet – how do we know when it has a charge? Does Mars have a charge? Does Earth? And are they the same charge? Otherwise they would be affected differently by the plasma in the solar system.

In regard to Olbers, I am aware of formal explanations. My question remains.

Moreover:

Originally Posted by ChipB View Post
The energy of photons from very old and distant stars is reduced by red shift.
All of the distant stars we see are very old. Moreover, redshift affects each and every star. If there is a single case when it doesn’t, then cosmic expansion is proven wrong, in my view. What do you think?

Thanks.
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Old Oct 9th 2013, 12:51 PM   #4
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Originally Posted by neil View Post
If plasma has mass and is therefore affected by gravity, it also means it provides its own gravity. So I suppose the question remains: how much of the gravity Mars ‘feels’ is from the Sun and how much from plasma? Remember that 99% of the (normal) matter is plasma.
The main gravitational influencers on a planet like Mars are (a) the sun, (b) other planets, specifically those relatively close by such as Jupiter and the Earth, and (c) to lesser extent the other planets. The mass of plasma in the solar system is extremely small compared to the mass of the sun itself. And it's distributed throughout the solar system. which means that the net effect of gravity from plasma on a planet is zero. The reason is that for every particle of plasma that is, say, 10KM from you in the north direction there is typically another particle 10 KM away in the south direction, and consequently the combined gravitational effect of them acting on you is zero. In a similar way if you are positioned inside a shell of material the net gravitational effect of that shell is zero. Think of the universe as an infinite series of shells filled with matter in a homogenous way, and the net effect of gravity on you (or Mars) from all those shells is .. zero! The math that proves this is fairly simple - I can walk you through it if you like.

Originally Posted by neil View Post
As for the charge of a planet – how do we know when it has a charge? Does Mars have a charge? Does Earth? And are they the same charge? Otherwise they would be affected differently by the plasma in the solar system.
Earth is considered to have zero charge. How do we know? Well, if it had an appeciable electric charge you could measure it, and you could make a hovercraft charged with opposite polarity that would fly without wings or an external ernergy source. No one has done that yet, so it's pretty clear that the net charge is zero. On a more serious note - the natural state of "cool" matter is neutral charge, meaning the number of electrons = number of protons. For the Earth to gain a charge some mechanism would have to either strip electrons from Earth and carry them into space or capture electrons from space. But it's a self-correcting mechabnism - if the Earth somehow gained a slight negative charge it would start attracting positive ions from space, thus becoming neutral again.

Originally Posted by neil View Post
In regard to Olbers, I am aware of formal explanations. My question remains.
What's your question? I though it was about Olber's Paradox and why the night sky is dark.


Originally Posted by neil View Post
Moreover, redshift affects each and every star. If there is a single case when it doesn’t, then cosmic expansion is proven wrong, in my view. What do you think?.
Not quite right. Hubble's constant defines the average red shift over a large volume of space, and does operate to affect every star we see, but within any section of space the individual star and galaxies have random components of motion that may overwhelm the amount of red shift that we actually measure. It's like leaves drifting on a lake - the general motion of the water current is from one end of the lake to the other but two leaves that are near each other may randomly drift closer together or further apart as they move along, and any wind will totally swamp out the effect of the general water current. The value of Hubble's Constant is approximately 80 Km/s/M-parsec, which isn't very much. For a star that is, say, 10 lightyears from Earth (3 parsecs), the red shift due to cosmic expansion is 80 Km/s/M-psec x 3 parsec = 0.64 Km per hour. This small value is totally swamped by the random motion of the star. This is why surveys of stars in the vicinity of Earth show essentially a random distribution of stars drifting towards us or drifting away. Now consider something much further away, like the Andromeda Galaxy, which is about 2.6 MLY or 800,000 parsecs away - the red shift due to cosmic expansion is 165,000 KPH, but even that is less than the relative motion of Andromeda to our galaxy. In fact the Andromeda galaxy is approaching us, not moving away. You have to look at galaxies that are at least several million parsecs from us before the cosmic expansion overwhelms the effects of local motions and the underlying nature of Hubble's Law becomes clear. Bottom line is the universe is expanding per Hubble's Law, but its hard to detect the effect on objects that are relatively close by.

Last edited by ChipB; Oct 11th 2013 at 11:35 AM.
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Old Oct 10th 2013, 09:09 AM   #5
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ChipB, I will take my time to reflect on your answers.

Thank you so much for your kindness.
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Old Nov 27th 2013, 02:14 PM   #6
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Originally Posted by neil View Post
If plasma has mass and is therefore affected by gravity, it also means it provides its own gravity. So I suppose the question remains: how much of the gravity Mars ‘feels’ is from the Sun and how much from plasma? Remember that 99% of the (normal) matter is plasma. At this point I don’t think the Newtonian view is accurate. Neither is Einstein. That or somehow all the plasma in the solar system has no gravitational effect whatsoever – but then we would have to explain why.

As for the charge of a planet – how do we know when it has a charge? Does Mars have a charge? Does Earth? And are they the same charge? Otherwise they would be affected differently by the plasma in the solar system.

In regard to Olbers, I am aware of formal explanations. My question remains.

Moreover:



All of the distant stars we see are very old. Moreover, redshift affects each and every star. If there is a single case when it doesn’t, then cosmic expansion is proven wrong, in my view. What do you think?

Thanks.
99% of matter is plasma and for the most part the plasma form of matter in our solar system is in the sun. Most of the rest of the solar system is composed of normal matter. Some exceptions outside the sun would be in particle accelerators and nuclear reactors and interestingly enough... fluorescent light bulbs! So if most of the gravitational pull on mars is the sun, most of the gravitational pull is from plasma.

I think that red shift may be more from gravitation than from space expansion.
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Old Nov 27th 2013, 02:50 PM   #7
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Originally Posted by Troll View Post
I think that red shift may be more from gravitation than from space expansion.
Red shift due to spatial expansion in the Solar System is not negligible...it is so small to be completely unmeasurable. But the GR redshift of light from the Sun is also pretty small and can't really be measured because it's swamped out by the movements of the plasma currents on the surface of the Sun.

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