Questions tagged [matter]

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157
votes
13answers
23k views

Why does space expansion not expand matter?

I have looked at other questions on this site (e.g. "why does space expansion affect matter") but can't find the answer I am looking for. So here is my question: One often hears talk of space ...
173
votes
3answers
66k views

Why doesn't matter pass through other matter if atoms are 99.999% empty space?

The ghostly passage of one body through another is obviously out of the question if the continuum assumption were valid, but we know that at the micro, nano, pico levels (and beyond) this is not even ...
46
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8answers
5k views

Why isn't dark matter just ordinary matter?

There's more gravitational force in our galaxy (and others) than can be explained by counting stars made of ordinary matter. So why not lots of dark planetary systems (i.e., without stars) made of ...
3
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2answers
603 views

What kind of matter are black holes made of?

Imagine a black hole originally formed from, for example, Rubidium atoms. On the other hand, one made from, for example, Helium atoms. Will it be there any difference between the two? Or perhaps once ...
31
votes
3answers
5k views

Is Dark Matter called “Matter” only because of gravity?

As far as my understanding goes, dark matter is nothing but an amount of gravitational force, from yet unresolved/undiscovered source(s), needed to explain some observed attributes of our universe. ...
23
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2answers
8k views

How do we know Dark Matter is non-baryonic? [duplicate]

It seems widely stated, but not thoroughly explained, that Dark Matter is not normal matter as we understand it. Wikipedia states "Consistency with other observations indicates that the vast majority ...
14
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5answers
70k views

When does 'energy' turn to matter?

I always hear about matter converting to 'energy' - fusion, fission. When does it go the other way around? What conditions lead to it? Are there reproducible experiments on this topic?
13
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4answers
8k views

Is it possible to create matter? [duplicate]

Is it possible to create matter? In a recent discussion I had, it was suggested that with enough energy in the future, "particles" could be created. It seems like this shouldn't be possible due to ...
9
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4answers
3k views

Where does matter go after reaching singularity in uncharged black holes?

I am a layman in physics and just read about black holes on the internet. I read that matter encounters geodesic incompleteness in the singularity in an uncharged black hole. I heard an analogy of ...
8
votes
2answers
692 views

How come the universe is made of matter and not antimatter?

Antimatter is like matter on opposite day: it has the same properties as the stuff that makes up planets, stars and galaxies, but one vital piece is different—its charge. The universe supposedly ...
4
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2answers
912 views

How do particles interact in Bohmian mechanics / pilot wave theory / de Broglie–Bohm theory?

I've read that in the de Broglie–Bohm interpretation of QM, the particle directed by its wavefunction has a trajectory (meaning both position and velocity) and that these are the only properties ...
1
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3answers
2k views

Is the empty space really empty? [duplicate]

I've come across another article in "list verse" which says that the empty space is not actually empty at least for a while. I've tried to find about this, so I googled it .It also quotes a word "...
0
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1answer
73 views

Basic energy question

How do we know something contain energy or not? P.S.: I don't really understand how energy should be interpreted. Until today I always thought that energy is some kind of magic that makes stuff ...
18
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4answers
3k views

Could quantum fluctuations spawn real matter?

Would it be plausible for fluctuations in the QED vacuum to spawn actual matter (such as quarks, electrons the constituents of a hydrgen atom) given enough time and space?
2
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1answer
284 views

Is the expansion of space universal or local?; does matter impede the expansion of space?

Michael Strauss in his recent book "Welcome to the Universe" with authors Tyson & Gott describes that space is NOT expanding within galaxies but rather between galaxies. So then the expansion is ...
15
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6answers
2k views

Why must a singularity form inside a black hole? [duplicate]

What is the exact reason that normal matter can not exist within an event horizon? I can understand how a super-dense object like a neutron star could accrete mass until its physical radius is less ...
7
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3answers
2k views

Where does the majority of the mass of the usual matter come from? [duplicate]

I apologize in advance to experts for the naivety of the question. It should be a duplicate but I didn't find any satifying question or answer about that. The proton is composed by two up quarks ...
4
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1answer
3k views

Is there an Ideal Liquid Law? Or Solid Law?

There is an Ideal Gas Law, but why isn't there one for liquids or solids? Is it because they are much too hard to predict or that solids and liquids vary drastically in their reaction to temperature ...
4
votes
4answers
15k views

What is negative Energy/Exotic Energy?

So I have been researching around a little as I am highly interested in Astrophysics and I came across an energy I have never heard of before; negative energy also commonly known as exotic energy. Now ...
3
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3answers
952 views

Are stars getting more metal-rich, less massive and shorter-lived with cosmic time?

A star produces energy through nuclear fusion with the 2H and 3H isotopes to create 4He for example. I read that there is a mass loss of 0.018884 (in atomic mass units). Of course this mass loss is ...
2
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1answer
379 views

X-Ray/Gamma Ray shielding: density versus conductivity

When talking about gamma ray or x-ray propagation in media, we usually talk about the mass attenuation coefficient, and we desire high density materials for shielding. This seems probabilistic: we ...
2
votes
2answers
239 views

Are there different kinds of antimatter reactions?

Obviously, when matter and antimatter collide, they annihilate. But how exactly and are all reactions the same? For example, what happens when a molecule of hydrogen meets a single pion? Does the ...
0
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8answers
2k views

Can I throw a stone through my window without breaking the glass?

As far as I know, most of an atom is vacuum. Therefore, in theory, would it be possible for me to throw a tiny stone through my window without breaking it because no matter actually collides?
17
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4answers
11k views

What would happen to matter if it was squeezed indefinitely?

I hope that this is a fun question for you physicists to answer. Say you had a perfect piston - its infinitely strong, infinitely dense, has infinite compression ... you get the idea. Then you fill ...
6
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3answers
2k views

What is the meaning of “matter” in physics?

What is the meaning of matter in physics? By defining matter in terms of mass and mass in terms of matter in physics, are we not forming circular definitions? Please give a meaning of "matter" in ...
2
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6answers
2k views

Mass without Matter?

My cursory studies of general relativity had introduced me to the concept of how gravity is associated with the warping of spacetime and that the presence of matter in space warps space and this ...
15
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3answers
3k views

How would neutron matter appear to the naked eye?

Neutron matter is matter comprised entirely of neutrons, as it exists in neutron stars. Most optical phenomena encountered in everyday life, such as light reflection and spectral absorption (i.e. ...
8
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3answers
1k views

Is there a giant cloud of antimatter at centre of the Milky Way

Among others, this page says there is a giant cloud of antimatter at centre of the Milky Way, which was discovered in the 1970s. My brother doesn't believe there is any such cloud. I'm prepared to ...
2
votes
1answer
375 views

In Bohmian mechanics, how does the particle's position affect where a particle is detected?

In Bohmian mechanics / pilot wave theory / de Broglie–Bohm theory, my understanding is that a particle's trajectory evolves based on its wave function, and that the position that particle is detected ...
6
votes
1answer
2k views

If atoms are mostly empty space, why doesn't light pass through everything?

Atoms are mostly empty space, and although I now understand why matter doesn't pass through other matter, why don't photons pass through the empty space of the atoms? Is it the same sort of idea as ...
6
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4answers
424 views

Which one is more fundamental in nature: matter or radiation?

I am following a geometric perspective on abelian gauge theory as done in the lecture notes by Timo Weigand, chapter 6, pp 165-167, here: http://www.thphys.uni-heidelberg.de/~weigand/QFT1-13-14/...
4
votes
1answer
150 views

Darkest matter on Earth (“pure black”)

What is (for a human's eyes) the natural or synthetical matter on Earth (i.e. not in Space) that emits the least quantity of visible photons while being lightened by sunlight? In this matter, how is ...
3
votes
1answer
441 views

What is the difference between matter & spacetime? [duplicate]

If the universe is expanding why doesn't the matter in it expand proportionally making it seem as if the universe is static? Alternatively, as spacetime expands why does it not just slide past matter ...
3
votes
1answer
104 views

Baryon asymmetry still going on

I read these questions and answers and it made me curious. Baryon asymmetry Why do we believe baryon asymmetry? Why does matter-antimatter asymmetry only refer to baryon asymmetry? How does ...
2
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2answers
3k views

Can matter have 100% reflection?

Is it possible to have matter that reflects all the light and does not absorb light at all? If thats possible then we can store light inside it right? I think we can trap light inside that matter in ...
2
votes
5answers
2k views

Why is the definition of mass and matter interlinked?

In my textbook the definition of matter and mass are: Matter: Any thing that occupies space and has mass . Mass: The amount of matter contained in a body. While defining "matter" we refer to "mass",...
1
vote
3answers
90 views

Does every material thing just consist in forces?

My dad's an aeronautical engineer. The other day, I visited a pub with him. A friend of his introduced him to someone who told us he was an electrical engineer. My dad replied with what I presume was ...
1
vote
2answers
457 views

What exactly is $T_{\mu\nu}$?

Continuous matter is described in special relativity by the matter tensor which is the so-called stress-energy-momentum tensor. I am finding a difficulty understanding how a tensorial tool (...
-2
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2answers
1k views

Can matter be converted to information?

I know that matter can be converted to energy through E=mc^2. I also know that engery can be and has been converted to information through Landauer's principle (with Maxwell's demons). Does this ...
5
votes
3answers
129 views

Cosmological Inflation: If Photon expands, why not other matter?

I keep repeatedly reading in many Stack Exchange and Quora questions that space of universe expands but particles (matter) don't, see e.g. this Phys.SE post. The reason given is that particles are ...
2
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2answers
368 views

Matter vs. Antimatter shortly after Big Bang

I am not a physicist or astronomer in training at all, so this might be a dumb question with an obvious answer, but as I watched something the other day on matter & anti-matter, and the discussion ...
1
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0answers
30 views

Does stripping electrons from atoms or adding them effect the state of matter in any way?

Does electric charge effect melting, boiling point or sublimation temperature?
1
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2answers
100 views

Do gravitational sources move along ‘geodesics’?

Assume we have a system of say two bodies which are orbiting each other. Now assume that we wish to find an equation of the orbits of the two gravitational sources. Do they follow a ‘geodesical’ path, ...
1
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2answers
3k views

Can energy exist without matter? [closed]

Is it theoretically possible that energy will be in space without any matter/antimatter/etc in that space? Is it theoretically possible that space will exist with only energy in it and without ...
1
vote
2answers
476 views

Conversion of energy to matter? [closed]

Now, this answer has sort of been asked before. But I haven't really found the answer that I'm looking for. Exactly what is the mechanism by which energy can be converted into matter? By "mechanism"...
1
vote
2answers
514 views

Feynman Diagrams: Mass Conservation

Can a Feynman diagram end with more matter than it began with? The answer should be no because it would break the law of conservation of mass, right? Example: I learned that two up-quarks could ...
0
votes
1answer
43 views

Is there scientific evidence that point towards the cause of differently distributed matter through out the Universe? [closed]

If we know from discoveries from cosmology prove that ordinary matter and dark matter are still not enough to explain the structure of the universe and its distribution of matter. There should be a ...
0
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3answers
1k views

Treating matter waves as light waves?

Is it valid to treat a matter wave as a light wave with wavelength equal to the de Broglie wavelength of the matter wave? Either way please can you explain why?
0
votes
1answer
378 views

Force on matter in inhomogeneous magnetic field (diamagnetism and paramagnetism)

I found on this site a formula (4.101). It describes wich force acts on matter in an inhomogeneous magnetic field. $ F_z = m_z * \frac{\partial B_z (z0)}{\partial z}$ What does the fraction consist ...
-2
votes
3answers
928 views

If mass is not conserved but instead energy is conserved, is it right to say that the fundamental particles are photons? [closed]

If mass is not conserved but instead energy is conserved, so is it right to say that the fundamental particle of the Universe is photon instead of protons, neutrons, electrons, leptons, etc and all ...