Thread: dark matter

hello
I have a question about dark matter

*dark matter would be matter with a mass (and gravity)but it is said it doesn't affect light

the problem I have is that
*black holes( or anything with an huge mass) are told to have sutch an inmense gravity that even light woudn't be able to escape from it

if both of these statements are right how is it possible that dark matter would not affect light and it has gravity

thanks
a young scientist

Originally Posted by sportlaan

hello
I have a question about dark matter

*dark matter would be matter with a mass (and gravity)but it is said it doesn't affect light

the problem I have is that
*black holes( or anything with an huge mass) are told to have sutch an inmense gravity that even light woudn't be able to escape from it

if both of these statements are right how is it possible that dark matter would not affect light and it has gravity

thanks
a young scientist

Dark matter does not interact with light electromagnetically. In other words, it doesn't reflect or absorb light, so light can't be used to see it. It does interact with light gravitationally.

Look up 'gravitational lensing'.

To add to AlexG's response, it is this gravitational lensing that supplies part of the evidence for Dark Matter. When we look at a galaxy we see more graviataitonal lensing than can be explained by the visible matter in the galaxy.

With the Bullet cluster, we even see gravitational lensing where there is no coresponding concentration of visible matter. The Bullet cluster is an example of a collision between two galaxy clusters, and the prevailing explaination is that the collision has separated the dark matter concentrations from the visible matter concentrations.

ok thank you
I don't really understand this gravitational lensing (I am yust a student of a secundairy school but I enjoy science a lot.
but I have another question:
what is light
I know light is a form of energy and that mass is a form of energy
so is light a form of mass ?(does light have a mass if so what?)
what form does light have?
and last but not least
why is the speed of light the maxium speed why can't there be a particle that can go faster?

I don't really understand this gravitational lensing

Just like a glass lens can bend the light that shines on it's entire surface into a single point, concentrating the light, gravity can do the same thing over intergalactic distances.

Mass is not a form of energy. There is an equivalence between mass and energy, but that does not mean mass is energy. Energy isn't a 'thing' in and of itself. It's a property of things.

why is the speed of light the maxium speed

The equations which describe speed and energy tell us that for an object with mass to accelerate to the speed of light would require an infinite amount of energy.

The ultimate answer to 'why' is 'because that's the way it is'.

ok thanks ^^
I have another question
why is matter out of our everyday life built up out of protons and neuterons(and electrons but they don't matter right now)
why can matter not just be built up out of neutrons (I know the sun makes energy out of it so would they just decay or somthing like that?)
I will propably keep the questions coming becous I allways find new one's

Originally Posted by sportlaan

ok thanks ^^
I have another question
why is matter out of our everyday life built up out of protons and neuterons(and electrons but they don't matter right now)
why can matter not just be built up out of neutrons (I know the sun makes energy out of it so would they just decay or somthing like that?)
I will propably keep the questions coming becous I allways find new one's

A free neutron, one not in a nucleus, spontaneously decays into a proton plus a positron plus a neutrino. This reaction can occur because the neutron has a larger mass than a proton. The at-rest energy of a particle is E = m c² , and there is enough energy in a neutron to produce a proton, positron, and neutrino, plus some left over for kinetic energy. Inside a nucleus, however, the energy is more complicated due to the nuclear interaction. The nuclei that exist have a rest-energy rather less than the sum of the rest-energies of the neutrons and protons that make them up. In this case, the neutron -> proton reaction is permitted only if the rest energy of the resulting nucleus is less than the rest energy of the original one. In particular, if there were a nucleus composed only of neutrons it would quickly have several of its neutrons turn into protons. So in the end we must have some protons around, or else the neutrons will decay.

There is a more subtle complication that raises the energies of bound states consisting only of neutrons, making most of them immediately fall apart into free neutrons even faster than the neutrons decay. I can tackle that also if you wish.

Originally Posted by sportlaan

what is light

Light is electromagnetic radiation of a certain frequency. Ultimately that means that light is made up of oscillating electric and magnetic fields arranged in a certain pattern; that wave propagates at a fixed speed, which is related to certain properties of the vacuum.

why is the speed of light the maxium speed why can't there be a particle that can go faster?

That is not something I can adequately explain in just a sentence or two. The ultimate reason is the geometry of space-time itself; light moves on special trajectories called null geodesics, which are located on geometric surfaces called light cones. If you do the maths it turns out that no material object can be accelerated to the speed of light, but also that light itself experiences no acceleration. For that reason it is impossible to exceed its speed.
As I said, the underlying principles are investigated in the Theory of Relativity, which deals with the geometry of space-time.

ok I understand but why does light not slow down ?

Originally Posted by sportlaan

ok I understand but why does light not slow down ?

Think of it this way - the speed of light is a function of two properties of the vacuum, called permittivity and permeability. The relation is simply



Since both of these are fundamental constants ( i.e. they're the same everywhere and never change ), light never speeds up and never slows down. In other words - it cannot be accelerated, as stated before.

In a wider sense, there is a general law in nature that massless particles always move at exactly the speed of light. They cannot do anything else.

you said light is massless how can it be it is made out of particles who have mass like neutrons?
and if it's massless what are the other massless particles?
I have another question: is heath a particle?

Originally Posted by sportlaan

you said light is massless how can it be it is made out of particles who have mass like neutrons?

Light is not composed of massive particles like neutrons. Light is composed of Photons.

Originally Posted by sportlaan

and if it's massless what are the other massless particles?

It appears that there are no massless particles. But photons are not particles.

Originally Posted by sportlaan

I have another question: is heath a particle?

Is what a particle?

Originally Posted by sportlaan

you said light is massless how can it be it is made out of particles who have mass like neutrons?

The carrier particles of light ( and all electromagnetic radiation ) are called photons. They are different from neutrons in that they are massless, and in that they are elementary ( i.e. they are not composed of other, smaller particles ). They do carry momentum, however.

and if it's massless what are the other massless particles?

There is only one other confirmed massless particle, the gluon. Gluons are the mediators of another fundamental interaction of nature, the Strong Force.
Hypothetically, there could be a mediating particle for gravity as well, called the graviton; that one would also be massless. However, gravitons have not been observed and are thus hypothetical.

I have another question: is heat a particle?

No. Heat is basically just energy which is transferred between systems; this transfer can take place in a variety of ways, one of which is radiation ( = photons again ), but heat itself is not a particle.

Gluons- I'm an idiot

Originally Posted by Neverfly

It appears that there are no massless particles. But photons are not particles.

Particle physicists consider a photon to be a particle, one of the gauge bosons. It is not essentially different from the range of other particles. Perhaps since it is the carrier of electromagnetism, which is intimately involved in General Relativity, it may be special if we ever get a theory that handles the incompatibilities between General Relativity and Quantum Mechanics. However, that possible difference is just a speculation.

I was misunderstood with the light beeing made out of neutrons I meant it like in the sun He becomes transferred to H and the neutrons become energy as light is a form of where does the mass go?

oh okay in a totally unrelated topic:
I have an exam chemistry wednesday does anybody have any tricks to remember the oxidationnumbers for example O : -II
without mendlejev

Ok i guess i ll have to study some more I have a other question for you geniusses a deep one, if the universe is a giant cpu and it worcks with laws as e=mc2what would be the formulla for speed?

Well i mean a car drives at a speed of 80 km/h explain the existance of speed what is it How does it exist? I know this is realy a weird question but everything in this universe should be explainable ,i think ...

Is there a certain relation with time and speed that can be written in a formulla in the way that speed affects time as they say a black hole's gravity would do?

The formula for speed is:

speed = distance/time

Originally Posted by sportlaan

Is there a certain relation with time and speed that can be written in a formulla in the way that speed affects time as they say a black hole's gravity would do?

Or here is an online calculator, which also shows you what the numbers mean:

http://www.1728.org/reltivty.htm

LOL @ "reltivity."

I just tought of a other one Is it possible there would be small sub-atomic particles who make sound possible
Or is it 100% atoms which vibrate?

Originally Posted by sportlaan

I just tought of a other one Is it possible there would be small sub-atomic particles who make sound possible
Or is it 100% atoms which vibrate?

There is no reason why one would accept the former statement, because sound is solely described in terms of oscillating pressure in a medium.

I'm sorry I don't understand what you mean

Originally Posted by sportlaan

I'm sorry I don't understand what you mean

Sound ('saund):
mechanical radiant energy that is transmitted by longitudinal pressure waves in a material medium (as air) and is the objective cause of hearing
(Merriam-Webster)

As you can see, the mechanisms behind sound are explained by pressure waves.
These pressure waves with alternating (oscillating) peaks of compressed medium (white lines) and valleys (black areas) where the molecules of the medium are farther apart (as depicted in the image), carry energy.

You do not need the existence of a subatomic particle in order to explain sound and its phenomena.

Originally Posted by sportlaan

I just tought of a other one Is it possible there would be small sub-atomic particles who make sound possible
Or is it 100% atoms which vibrate?

Sound is molecules banging into other molecules banging into other molecules, and so on down the line.

why do atoms want 8 (

Originally Posted by AlexG

Originally Posted by sportlaan

I just tought of a other one Is it possible there would be small sub-atomic particles who make sound possible
Or is it 100% atoms which vibrate?

Sound is molecules banging into other molecules banging into other molecules, and so on down the line.

THAT is the explanation I understand
a question which has more to do with chemistry:
why do atoms want 8 or 2 electrons on their outer circle? and not like 7 or 1?

yes but could you explain this into quantum mechanics
I know they are the most stable on that way but why?

thanks ^^

i have a question about e=mc² of einstein
e=energy
m=mass
c=the speed of light
wouldn't this mean that energy is a lot of mass and not the other way around
can someone explain to me why this would mean that mass can be convertde in lots of energy and not energy = lots of mass?

i know that this is what it means I just don't understand that if e=m xmc²
why mmass would be a lot of energy
I would say it means energy is a lot of mass
am I doing somthing wrong in my maths?

ok thanks now I understand
in my book chemistry I have to learn about rutherfort who shot a small metal plate with alfa rays and watched where they wend by a ZnCl screen
wasn't his experiment totally unnecessary becous light does the same with matter like air?

well ok but that light allso passes thru air also will say the atom is very open and the mass is in the nucleus
we have to learn 3 points he made up from his experiment and this is already 2
a good start if you don't need radioactives for it I would say!

I have a question about energy
I've read there is an anti-particle for any particle
is there something like anti-energy in these anti-particles?

what is light's charge?
I mean relative to a proton or an elektron.

why do they react with electrons if they don't have a charge?

ow ok
I've read an article in the newspaper about a microscope which would be able te count atoms and tell of what sort they are is this actually possible?

ow ok so it is possible to see a atom if you've got a good microscope?

Originally Posted by SpeedFreek

Originally Posted by sportlaan

Is there a certain relation with time and speed that can be written in a formulla in the way that speed affects time as they say a black hole's gravity would do?

Or here is an online calculator, which also shows you what the numbers mean:

RELATIVITY CALCULATOR

thank god for that calculator where do fysicists even get these symbols from?
I would like it to do something whit fysics later but these symbols
I would never be able to memorize them

About these things in fysics : Isn't ther much we try to explain which we will never be able to use in our own advantage like ?
I realy like it to understand the ways of nature in the other hand
How do you guys understand all these things ?
what jobs do you have: making gold out of other metals?

Serious what kinds of jobs are there with quantum mechanics ? What do you guys do for living?

Originally Posted by sportlaan

am I doing somthing wrong in my maths?

You haven't done any math.

Originally Posted by Neverfly

Originally Posted by sportlaan

am I doing somthing wrong in my maths?

You haven't done any math.

I have done maths I just didn't type them

Originally Posted by PhDemon

I work in a university chemistry department doing research into the chemistry and physics of the atmosphere and small (micron sized) particles.

cool have you discovered anything special and is it a fun job?

I havn't seen you ever beeing offline when do you work?
does it pay good to work at a lab?

ok
i had an exam french today (I'm really bad at french)
where you good at languages when you were young?
I have an exam fysics tomorrow it's the last exam ,finally!!!
I don't like the kind of fysics we have to learn : gravity, powers, ...
always how it works but never why it works
when do you quantum fysics?

I know i have to learn the basics but they are so...logical that they get boring very fast
I have read a lot about science when I was a bit younger so I already know most of the stuf

Originally Posted by PhDemon

Originally Posted by sportlaan

I know i have to learn the basics but they are so...logical that they get boring very fast

If you find the logical development of ideas boring maybe science is not for you

Originally Posted by sportlaan

I have read a lot about science when I was a bit younger so I already know most of the stuf

I meant the kind of stuff we learn from our teacher

Not being rude but judging by your questions here I think you're kidding yourself

I like the logical development of ideas i just think if somthing is to logical it get's boring faster than somthing weird like quarks

talking about quarks is more intresting than talking about how a spring will try to stay in a certain state

I hope you're right I'll come back when I finished my studies
but the thing is I enyoy it more when I understand somthing what is very difficult than if i understand the basics.
I think by the way there isn't really another option than sience for me : I don't like art, I am bad at languages and I am terrible at sports

I don't understand the difficult stuff you're right.
but my point was you can't realy get satisfaction if you understand the basics I can't get no SATISFACTION

You can get satisfaction just fine. You're acting as though the basics are all there is- that is not the case.
You can get satisfaction out of your day just fine, even though your day is chock full of basics like toothbrushing, peeing, tying shoes, etc.

Originally Posted by Neverfly

You can get satisfaction just fine. You're acting as though the basics are all there is- that is not the case.
You can get satisfaction out of your day just fine, even though your day is chock full of basics like toothbrushing, peeing, tying shoes, etc.

yes but I don't get satifaction on the way of thinking "O_o how did I understand that" from my everyday basics
the problem is and will allways be this way that
"when you're young you want to be old and understand but if you are old you want to be young again and be simple"

hmm I thougt about a post of someone which said a massless automaticly has the speed of light is this true
if gravitons exist would they travell by the speed of light?

so that would (I think) kind of explain why light is affected by gravity?
I mean gravity would be fast enough to catch up with light.
is this right?

Originally Posted by sportlaan

so that would (I think) kind of explain why light is affected by gravity?
I mean gravity would be fast enough to catch up with light.
is this right?

No. Light is affected by gravity because light will always travel along the geodesic, and gravity bends the geodesic.

So what would gravitons do here gravitons are theorized to be gravity right?

Originally Posted by sportlaan

Serious what kinds of jobs are there with quantum mechanics ?

Semiconductor process design. And coming up with new technologies that will replace traditional semiconductors when we get to the point they are no longer viable (10 to 20 years).

What do you guys do for living?

Design microprocessor chips using the semiconductor processes that the guys who understand the physics come up with!

quote PhDemon,

100 Philistine Foreskins

and David said:

‘Does it seem to you a little thing to become the king’s son-in-law, seeing that I am a poor man and of no repute?’ The servants of Saul told him, ‘This is what David said.’ Then Saul said, ‘Thus shall you say to David, “The king desires no marriage present except a hundred foreskins of the Philistines, that he may be avenged on the king’s enemies”‘. Now Saul planned to make David fall by the hands of the Philistines. [1 Samuel 18:20-25 (NRSV)]

Accordingly King Saul believed that if David tried for the challenge that he would be slain for his efforts, thereby thwarting the Kings daughter's infatuation with David. But accordingly David went forth with an army and delivered the foreskins, and consequently married the king's daughter.

I guess the moral of the story is that delivering many foreskins can get you a fine woman and great power -- maybe even just Philistine goat foreskins?

(just) A Little Knowledge Is A Dangerous Thing

(parenthesis added) maybe today's state of affairs?