Dark Matter - A stray Thought

. I was wondering, are there any estimates for the overall gravity caused
by
subatomic particles, particle radiation and... showing my ignorance of
physics here.. photons (if they have a gravitational effect - I know they
have a pressure & mass, which in turn implies gravity).

Hi Zed,

I thought photons were massless - thet's why it's called "light" :-)

Okay I'll shut up now...

In message , zed writes
With regards to the mass of a photon, have a look at this.....

http://www.physlink.com/Education/AskExperts/ae180.cfm

... anyone care to work out the mass of a helium neucleus (alpha radiation)
travelling at say 97% of the speed of light?

What I'm getting at is there must be a bloody large amount of gravitational
force in the universe caused by velocity induced mass. Every cubic
centimeter of space time must be packed full of photons and the like,
travelling every which way since the beginning of time.

Is it enough to bend the universe and curve space? Is this the "surface
tension" of the universe - the undetectable "dark matter"?

Answers on a postcard please!! )

No.

Relativistic mass isn't rest mass, and it's only rest mass that produces
gravity. So light doesn't produce any gravity at all, and the small
amount of matter in cosmic rays only produces gravity proportional to
its negligible mass (though the highest-energy cosmic rays have amazing
momentum and energy, about the same as a well-thrown cricket ball, IIRC)
--
"Roads in space for rockets to travel....four-dimensional roads, curving with
relativity"
Mail to jsilverlight AT merseia.fsnet.co.uk is welcome.
Or visit Jonathan's Space Site http://www.merseia.fsnet.co.uk

In message , zed writes
With regards to the mass of a photon, have a look at this.....

http://www.physlink.com/Education/AskExperts/ae180.cfm

... anyone care to work out the mass of a helium neucleus (alpha radiation)
travelling at say 97% of the speed of light?

What I'm getting at is there must be a bloody large amount of gravitational
force in the universe caused by velocity induced mass. Every cubic
centimeter of space time must be packed full of photons and the like,
travelling every which way since the beginning of time.

Is it enough to bend the universe and curve space? Is this the "surface
tension" of the universe - the undetectable "dark matter"?

Answers on a postcard please!! )

No.

Relativistic mass isn't rest mass, and it's only rest mass that produces
gravity. So light doesn't produce any gravity at all, and the small
amount of matter in cosmic rays only produces gravity proportional to
its negligible mass (though the highest-energy cosmic rays have amazing
momentum and energy, about the same as a well-thrown cricket ball, IIRC)
--
"Roads in space for rockets to travel....four-dimensional roads, curving with
relativity"
Mail to jsilverlight AT merseia.fsnet.co.uk is welcome.
Or visit Jonathan's Space Site http://www.merseia.fsnet.co.uk

On Sun, 20 Jul 2003 18:26:02 +0100, zed wrote:

... anyone care to work out the mass of a helium neucleus (alpha radiation)
travelling at say 97% of the speed of light?

We're only looking (roughly) at a 5-fold increase in mass for any object
travelling at 97% of the speed of light. For an alpha particle this would
mean that it would "weigh" around 0.000000000000000000000000003 kilograms,
its rest mass being around 0.0000000000000000000000000006 kilograms.
Sorry if I missed out a few noughts, but you get the point I hope.

Things get hairier the closer you push closer towards "c" however!

--
Regards,
Gareth Williams

On Sun, 20 Jul 2003 18:26:02 +0100, zed wrote:

... anyone care to work out the mass of a helium neucleus (alpha radiation)
travelling at say 97% of the speed of light?

We're only looking (roughly) at a 5-fold increase in mass for any object
travelling at 97% of the speed of light. For an alpha particle this would
mean that it would "weigh" around 0.000000000000000000000000003 kilograms,
its rest mass being around 0.0000000000000000000000000006 kilograms.
Sorry if I missed out a few noughts, but you get the point I hope.

Things get hairier the closer you push closer towards "c" however!

--
Regards,
Gareth Williams

"zed" wrote in message
...
With regards to the mass of a photon, have a look at this.....

http://www.physlink.com/Education/AskExperts/ae180.cfm

... anyone care to work out the mass of a helium neucleus (alpha
radiation)
travelling at say 97% of the speed of light?

What I'm getting at is there must be a bloody large amount of
gravitational
force in the universe caused by velocity induced mass. Every cubic
centimeter of space time must be packed full of photons and the like,
travelling every which way since the beginning of time.

Is it enough to bend the universe and curve space? Is this the "surface
tension" of the universe - the undetectable "dark matter"?

Answers on a postcard please!! )


Dark matter cannot be made up of relativistic particles, because it has to
be cold enough (equivalent to saying the particles have to move slowly) to
be retained in galaxies by gravitation. Recent data confirms that dark
matter is not uniformly spread around the universe (hot) but is clumped into
galaxy clusters and individual galaxies (viz. the dark matter in our own
galaxy that causes the rotation curve to have constant velocity of orbital
motion as you look further and further out in distance).

Whatever it is, it is NOT ordinary matter because it does not interact with
ordinary matter in any observed way except through gravity. For example, it
produces no observable light or infrared radiation at all, so there are no
"atomic" interactions.

Very peculiar stuff, whatever it is.

--
Mike Dworetsky

(Remove "pants" spamblock to send e-mail)

"zed" wrote in message
...
With regards to the mass of a photon, have a look at this.....

http://www.physlink.com/Education/AskExperts/ae180.cfm

... anyone care to work out the mass of a helium neucleus (alpha
radiation)
travelling at say 97% of the speed of light?

What I'm getting at is there must be a bloody large amount of
gravitational
force in the universe caused by velocity induced mass. Every cubic
centimeter of space time must be packed full of photons and the like,
travelling every which way since the beginning of time.

Is it enough to bend the universe and curve space? Is this the "surface
tension" of the universe - the undetectable "dark matter"?

Answers on a postcard please!! )


Dark matter cannot be made up of relativistic particles, because it has to
be cold enough (equivalent to saying the particles have to move slowly) to
be retained in galaxies by gravitation. Recent data confirms that dark
matter is not uniformly spread around the universe (hot) but is clumped into
galaxy clusters and individual galaxies (viz. the dark matter in our own
galaxy that causes the rotation curve to have constant velocity of orbital
motion as you look further and further out in distance).

Whatever it is, it is NOT ordinary matter because it does not interact with
ordinary matter in any observed way except through gravity. For example, it
produces no observable light or infrared radiation at all, so there are no
"atomic" interactions.

Very peculiar stuff, whatever it is.

--
Mike Dworetsky

(Remove "pants" spamblock to send e-mail)

On Mon, 21 Jul 2003 08:52:04 +0000 (UTC), "Mike Dworetsky"
wrote:



"zed" wrote in message
...
With regards to the mass of a photon, have a look at this.....

http://www.physlink.com/Education/AskExperts/ae180.cfm

... anyone care to work out the mass of a helium neucleus (alpha
radiation)
travelling at say 97% of the speed of light?

What I'm getting at is there must be a bloody large amount of
gravitational
force in the universe caused by velocity induced mass. Every cubic
centimeter of space time must be packed full of photons and the like,
travelling every which way since the beginning of time.

Is it enough to bend the universe and curve space? Is this the "surface
tension" of the universe - the undetectable "dark matter"?

Answers on a postcard please!! )


Dark matter cannot be made up of relativistic particles, because it has to
be cold enough (equivalent to saying the particles have to move slowly) to
be retained in galaxies by gravitation. Recent data confirms that dark
matter is not uniformly spread around the universe (hot) but is clumped into
galaxy clusters and individual galaxies (viz. the dark matter in our own
galaxy that causes the rotation curve to have constant velocity of orbital
motion as you look further and further out in distance).

Whatever it is, it is NOT ordinary matter because it does not interact with
ordinary matter in any observed way except through gravity. For example, it
produces no observable light or infrared radiation at all, so there are no
"atomic" interactions.

Very peculiar stuff, whatever it is.

That's for sure, considering it provides the majority of the universe's
mass.

--

wrmst rgrds
Robin Bignall

Quiet part of Hertfordshire
England

http://homepage.ntlworld.com/docrobin/homepage.htm

On Mon, 21 Jul 2003 08:52:04 +0000 (UTC), "Mike Dworetsky"
wrote:



"zed" wrote in message
...
With regards to the mass of a photon, have a look at this.....

http://www.physlink.com/Education/AskExperts/ae180.cfm

... anyone care to work out the mass of a helium neucleus (alpha
radiation)
travelling at say 97% of the speed of light?

What I'm getting at is there must be a bloody large amount of
gravitational
force in the universe caused by velocity induced mass. Every cubic
centimeter of space time must be packed full of photons and the like,
travelling every which way since the beginning of time.

Is it enough to bend the universe and curve space? Is this the "surface
tension" of the universe - the undetectable "dark matter"?

Answers on a postcard please!! )


Dark matter cannot be made up of relativistic particles, because it has to
be cold enough (equivalent to saying the particles have to move slowly) to
be retained in galaxies by gravitation. Recent data confirms that dark
matter is not uniformly spread around the universe (hot) but is clumped into
galaxy clusters and individual galaxies (viz. the dark matter in our own
galaxy that causes the rotation curve to have constant velocity of orbital
motion as you look further and further out in distance).

Whatever it is, it is NOT ordinary matter because it does not interact with
ordinary matter in any observed way except through gravity. For example, it
produces no observable light or infrared radiation at all, so there are no
"atomic" interactions.

Very peculiar stuff, whatever it is.

That's for sure, considering it provides the majority of the universe's
mass.

--

wrmst rgrds
Robin Bignall

Quiet part of Hertfordshire
England

http://homepage.ntlworld.com/docrobin/homepage.htm

OK - so what are we talking about here - does or does not relativistic mass
create a gravitational force? If it does, then does the spherical spread
pattern (assuming a galaxy as a point source) of photons and other
relativistic velocity particles contribute any measurable force which could
be attributed to dark matter? Dredging my old maths of 15 years ago here....
The density of such particles would obey an inverse cube law with distance
wouldn't they?

By the way... I know I'm flogging a dead horse here but it was such an
intriguing drunk thought I just don't want to let go just yet! )

"Dr John Stockton" wrote in message
...
JRS: In article , seen in
news:uk.sci.astronomy, Jonathan Silverlight
posted at Sun, 20 Jul 2003 19:12:22 :-

Relativistic mass isn't rest mass,

No need to argue with that.

and it's only rest mass that produces
gravity. So light doesn't produce any gravity at all,

I don't believe that. IIRC, the Eotvos experiment would, and did not,
show a difference; in some (heavy?) atoms, the relativistic contribution
to the total mass is non-negligible. So the mass of an atom at rest is
itself partly relativistic.

Inertial mass and gravitational mass are the same.

and the small
amount of matter in cosmic rays only produces gravity proportional to
its negligible mass (though the highest-energy cosmic rays have amazing
momentum and energy, about the same as a well-thrown cricket ball, IIRC)

I can believe that, but taking mass as including energy.

--
© John Stockton, Surrey, UK. /
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