Dark Matter or Dark Mass?

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  • #51
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Thanks Chalnoth,

I make that 2.725K x 1090 = 2970K
Also the radius of what is now the observable universe is just 300,000 light years, about 3 times the diameter of the milky way.
Also matter at that time had just taken the form of normal, non ionized Hydrogen and Helium atoms.
Is it in a gaseous form or is it much to dense? What is the density or pressure or number atoms per unit volume?
 
  • #52
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Any chance we can get back to the topic of the OP after the 30-post diversion on general cosmology?
 
  • #53
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Sorry. Maybe we can start a general Ad Hoc questions thread and copy it there?
 
  • #54
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We know particles have mass. Thusfar we don't know of anything that has mass which is not a particle so we assume the likeliest explanation for apparent missing mass must be missing particles.
particle-wave duality???

photons have no mass

what do you mean by a particle?

or a wave?

or mass for that matter
 
  • #55
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So, for instance, when the CMB was emitted at a redshift of [itex]z=1089[/itex], the temperature was 1090 times as high as it is today.
Does the speed of light remain constant as one goes back in time towards the initial Big Bang event?
 
  • #56
Chalnoth
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particle-wave duality???

photons have no mass

what do you mean by a particle?

or a wave?
In quantum mechanics, all matter has wave-like behavior. A quantum-mechanical particle is a quantum of a field. An electromagnetic field, for instance, is made up of tremendous numbers of quanta called photons, which we understand as being particles in the quantum-mechanical sense (which includes having wave-like behavior).

or mass for that matter
Mass is the non-kinetic energy of an object.
 
  • #57
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In quantum mechanics, all matter has wave-like behavior. A quantum-mechanical particle is a quantum of a field. An electromagnetic field, for instance, is made up of tremendous numbers of quanta called photons, which we understand as being particles in the quantum-mechanical sense (which includes having wave-like behavior).


Mass is the non-kinetic energy of an object.
E = mc^2

E = hf

so mc^2 = hf

which defines mass, m as

m = (h/c^2) f = Kf

Mass is merely a "vibration"

Notice how small the constant (h/c^2) is?
 
  • #58
Chalnoth
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E = mc^2

E = hf

so mc^2 = hf
Non-kinetic energy. Planck's constant times the frequency of a photon is the kinetic energy of the photon. Photons have no non-kinetic energy.
 
  • #59
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Non-kinetic energy. Planck's constant times the frequency of a photon is the kinetic energy of the photon. Photons have no non-kinetic energy.
....and yet photons exert pressure (photoelectric effect, solar sails)

interesting
 
  • #60
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I'm new to blogs so this is my first post. I'm also no physicist by any stretch of the imagination but I love science. My question is this, if light is slowed when it moves through a medium which has mass, and it seems the belief is that dark matter has mass and is everywhere, isn't light actually slowed by dark matter? It seems to me that if this is true then light should actually be faster than what we know it to be. If, for example, there was a true "vacuum" devoid of any dark matter would light travel faster or is the speed of light already based on a true vacuum with no dark matter in the equation?
 
  • #61
Chalnoth
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....and yet photons exert pressure (photoelectric effect, solar sails)

interesting
Yes, because photons also have momentum equal to their energy. In relativistic terms, the total energy of a particle is:

[tex]E^2 = p^2 c^2 + m^2 c^4[/tex]

Notice that in the case of zero momentum ([itex]p[/itex] is the momentum of the particle), this equation reduces to the more familiar:

[tex]E = mc^2[/itex]

This is actually just a special case, as the energy is only equal to the mass in the non-moving case. With photons, which have zero mass, the energy reduces to:

[tex]E = p c[/tex]

Since photons have momentum, they can impart that momentum on other objects when they are absorbed or bounce off of them. And so a bunch of photons hitting an object together exert pressure.
 
  • #62
Chalnoth
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I'm new to blogs so this is my first post. I'm also no physicist by any stretch of the imagination but I love science. My question is this, if light is slowed when it moves through a medium which has mass, and it seems the belief is that dark matter has mass and is everywhere, isn't light actually slowed by dark matter? It seems to me that if this is true then light should actually be faster than what we know it to be. If, for example, there was a true "vacuum" devoid of any dark matter would light travel faster or is the speed of light already based on a true vacuum with no dark matter in the equation?
Light isn't slowed by mass. It's slowed by electromagnetic interactions. So light is basically unaffected by dark matter, which has no charge with which light can interact.
 
  • #63
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[tex]E = p c[/tex]

.... p=[tex]\frac{h}{c}[/tex]f

Momentum is dependent on the frequency (or wavelength) of the photon

(just trying out the cool symbols etc availiable on this chat site)
 
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  • #64
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"Mass is the non-kinetic energy of an object." originally posted by chalonth

what do you mean by this i thought mass was the amount of matter inside an object
 
  • #65
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I'm interested to see Ich's response but in thinking about it, it's obvious that spacetime moves back to straight/flat if you take the matter away, so in that sense, it wants to be straight/flat.
i agree but then what would happen i too big of a mass made a rip in space time and then that mass dissapeared?(theoretically of course)
 
  • #66
Chalnoth
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"Mass is the non-kinetic energy of an object." originally posted by chalonth

what do you mean by this i thought mass was the amount of matter inside an object
Nope. If you have a block of wood, and raise its temperature, its mass increases. It just so happens that for reasonable temperatures, that mass increase is almost completely negligible. But for quantum systems the mass difference due to similar effects can be significant.

For example, if you compare the masses of a proton and a neutron separately, and then to a deuterium ion (which is a bound state of a proton and a neutron), you find that the deuterium ion has about 0.1% less mass. This is an indication that the deuterium ion is a lower-energy configuration than a separate neutron and proton.

Even more striking, however, is what happens inside the protons and neutrons. The masses of the individual quarks that make up the proton and neutron are only around 1-2% of the total mass. The rest of the mass comes from the binding energy of the quarks.
 
  • #67
Chalnoth
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i agree but then what would happen i too big of a mass made a rip in space time and then that mass dissapeared?(theoretically of course)
So far as we are aware, no amount of mass can cause anything like a rip in space-time.
 
  • #68
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Even more striking, however, is what happens inside the protons and neutrons. The masses of the individual quarks that make up the proton and neutron are only around 1-2% of the total mass. The rest of the mass comes from the binding energy of the quarks.
Intreresting....

Are you saying that whilst the quarks are bounded together inside the protons and neutrons that about 98% of that mass is in the form of binding energy?

It would seem to me that what happens is that this energy is released as a direct result of separating the quarks.

Whilst mass and energy can be interchanged - they are not equivalent states

One must be careful when comparing quarks on their own with quarks bounded together in a neutron or proton
 
  • #69
Chalnoth
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Intreresting....

Are you saying that whilst the quarks are bounded together inside the protons and neutrons that about 98% of that mass is in the form of binding energy?

It would seem to me that what happens is that this energy is released as a direct result of separating the quarks.
Nope, actually. The strong force doesn't allow that. If it did, protons would decay rather rapidly! The effect that prevents protons from breaking apart into their constituent states is known as "confinement", and it means that you have to put so much energy into a system to pull its quarks apart that soon quark/anti-quark pairs will pop into existence between the quarks you're pulling apart.

So in the case of, say, a proton, made of two ups and a down, if I started to pull on one of the quarks, eventually the tension would "snap", producing a quark/anti-quark pair. The new quark will bind with the proton, leaving it either as a proton or a neutron (depending upon whether the quark I leave behind is the same or different), and I'll be left holding onto the quark I was pulling on and an anti-quark in a bound state, which is known as a meson.

It turns out that the way the strong force behaves, protons are the lowest-mass configuration of three quarks, and you just can't pull them apart to make more energy. Other three-quark configurations all have more mass. This includes the neutron, which, if it is unbound, will decay into a proton, electron, and anti-neutrino after a little while. It's just that neutrons, when bound to protons, can be stable in some configurations.

Whilst mass and energy can be interchanged - they are not equivalent states
Nope, mass and energy are equivalent. Mass is non-kinetic energy. That is all.
 

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