All Questions
45
questions
0
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1
answer
62
views
What is the total mass-energy of baryonic matter?
From what I understand, conservation of energy does not apply to the total energy of the Universe, because it constantly expands and the new, created space has a constant non-zero energy of its own. ...
- 413
0
votes
0
answers
47
views
Transition to Neutron Star
If we're asked to believe that the explosive aspect of a supernova results from a rebound of residual free falling matter off of the stellar core, shouldn't we also be asked to believe that transition ...
user394592
0
votes
2
answers
104
views
Matter and Antimatter coexistence [closed]
Isn't it possible that matter and antimatter coexist? Recently, the ALPHA experiment at CERN has been looking into this topic. And I read about it from Fermilab's website, so they are saying how our ...
0
votes
1
answer
93
views
Event after big bang that cause dark matter [closed]
When the universe was formed by the Big Bang, what was the event that made some matter visible to us, while some became dark matter?
0
votes
2
answers
98
views
Mass matter, energy and "massless matter"
This is perhaps a rather silly question, or rather a matter of convention, but I would like to hear arguments about the appropriateness of certain definitions.
Traditionally, in chemistry and in pre-...
- 1,640
6
votes
1
answer
354
views
How would the universe look like without matter?
I was wondering how the universe would look like if it would have been perfectly symmetrical in terms of matter and antimatter. If I understand correctly, there would be no "particle" but ...
- 357
1
vote
0
answers
52
views
Expansion of the Universe inside mattar [duplicate]
When talking about the expansion of the universe we usually refer to the Friedman equations so we assume homogeneous and isotropic solution to Einstein field equation which is true on cosmological ...
- 1,734
2
votes
1
answer
93
views
Total number of particles in the universe (according to Planck Surveyor measures, 2018)
Recently, Marco Ajello et al. (2018) has estimated the total number of photons in the whole observable universe as:
$$N_\gamma \approx 4\cdot 10^{84}.$$
On the other hand, the ratio of baryons to ...
- 1,640
-3
votes
2
answers
267
views
Does anyone really know how dark energy/matter works?
If dark energy has no physical interaction with normal matter but it does interact with dark matter, wouldn't that cause an interaction with normal matter through its interaction with dark matter and ...
- 1
0
votes
1
answer
79
views
What are the conditions needed for baryogenesis? [duplicate]
Physicists have created antimatter in the laboratory. But when they do, they create an equal amount of matter. That suggests that the Big Bang must have created matter and antimatter in equal ...
user318515
2
votes
2
answers
464
views
Why do matter and radiation densities scale differently in expanding universe, when all matter is energy and all energy is matter? [duplicate]
I sometimes see the first Friedmann equation expressed with different terms for the density of "matter" and the density of "radiation". It is said that with an increase in scale ...
- 213
0
votes
1
answer
41
views
How the universe is expanding? [duplicate]
If universe is expanding with the velocity of light then why the distance between earth and sun is constant? Also why the distance from one Galaxy to another remains constant? And so on...
-1
votes
1
answer
87
views
Does the expansion of the Universe cause internal stresses in solids (and other substances with similar internal resistance forces)? [duplicate]
Is my understanding correct?
Weren't it for the internal resistance forces between particles in a solid object, the expansion of the Universe would continuously increase the distances between all of ...
- 245
2
votes
0
answers
59
views
Gravity in a universe where all energy has been turned to mass [closed]
If all energy in the universe was turned to mass would gravity work?
- 21
0
votes
3
answers
40
views
Are the constituents of the known universe matter (including antimatter) and electromagnetic radiation?
Is it correct to say that the constituents of the known universe are matter (including antimatter) and electromagnetic radiation, leaving aside the comparatively hypothetical ‘dark’ entities? This is ...
- 135
2
votes
1
answer
81
views
Amount of matter in two infinite universes [closed]
I don't know exactly where to find any other information on this question so I thought I would ask here. If there were two infinitely large universes one where 20% of the space in the universe was ...
- 21
0
votes
1
answer
104
views
Are there other theories than gravitational attraction taken into account as a reason for the extreme accumulation of matter in the universe?
This question is about how small the interstellar density is (less than 1 atom per cubic centimeter).
But although the interstellar density is very low, matter tends to extremely aggregate in certain ...
- 282
3
votes
3
answers
204
views
Expansion of space or contracting of matter? [duplicate]
Can the expansion of the Universe effect be explained by contraction of the overall matter instead? That is, all material objects are in fact contracting, due to what the universal space seems (and ...
- 31
0
votes
0
answers
34
views
Mass and Gravitational Force [duplicate]
Why do mass has a tendency to attract other masses and form bigger cluster of mass?
What cause gravitational force to exist?
Is it so that at one point of time all matter in universe will form ...
0
votes
1
answer
353
views
Pressure of (cold matter)
The first pages of Weinberg's Cosmology state that matter, cold matter like dust has zero pressure. I find it very disturbing. Does 'cold matter' also include fluids since hot matter is radiation, ...
- 487
0
votes
1
answer
111
views
What if there was no baryon-antibaryon asymmetry in our universe?
We know that the universe goes through different evolutionary phases: radiation, matter and later dark energy epoch.
What would happen if there was no baryon-antibaryon asymmetry? How would the ...
- 77
2
votes
0
answers
46
views
Is every object in the universe really expanding? Even small scale objects like humans? [duplicate]
So I was asked a question by someone that "if everything in the universe is expanding, then the lens we use to look at stellar objects is expanding as well, meaning we shouldn't be able to tell the ...
- 121
5
votes
3
answers
237
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 ...
- 149
0
votes
1
answer
614
views
As space expands does the density of matter remain same or increase? [duplicate]
I learned that space is always expanding. Even between sun and earth, it's just gravity is stronger.
Imagine space as graph paper and there is a square object that fills it.
Space expands, 1x1 cell ...
- 2,645
4
votes
2
answers
492
views
Intuition for why matter dominated expansion is faster than radiation domination?
In a matter dominated universe $a_{\rm mat.}(t)\sim t^{2/3}$, while in a radiation dominated universe, $a(t)_{\rm rad.}\sim t^{1/2}$. Therefore, a matter dominated universe is expanding more quickly, ...
- 3,492
-2
votes
1
answer
106
views
If energy can't order itself, how did energy get ordered or made? [duplicate]
In the universe we see that hydrogen (bound up energy) is found in a highly concentrated ordered state in some places and it's highly dispersed in most other places. There is a natural progression ...
0
votes
1
answer
167
views
Could matter in the universe come from some process other than the decay of inflaton field?
Could matter in the universe come from some process other than the decay of inflaton field?
Do we have any theoretical reasons that support the idea that matter was created from the decay of ...
- 855
0
votes
0
answers
55
views
Space expansion and conservation of energy [duplicate]
The phrase of 'expansion of universe' , as we are led to believe, is mostly referring to an expansion in space. But is space expanding in the sense that the space between two particles is increasing ...
- 126
1
vote
1
answer
756
views
How does mass affect the expansion of space?
I'm a layman and I'm curious to understand how mass affects the expansion of space and whether the expansion of space is uniform everywhere in the universe.
From looking at redshifts it seems we have ...
- 11
0
votes
1
answer
54
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 ...
- 13
1
vote
1
answer
66
views
Would "gravity" and the "law of gravity" have a meaning in a universe without matter?
I was discussing the fact that if there was no matter in the universe, just vacuum and radiation, can we say that anything called gravity wouldn't exist?
In that universe, the Friedman equations ...
- 93
0
votes
1
answer
464
views
Solving the Friedmann Equation for a specific universe
Suppose instead of the cosmological constant there is a quantum field with equation state parameter $w = -1/2$. Assume also it is a flat universe with only this quantum field ($Q$) and with non ...
- 21
6
votes
4
answers
598
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/...
user56963
12
votes
2
answers
2k
views
What is the physics definition of space?
When astronomers, physicists say that space is expanding, does the definition of space include matter, energy and the particles within?
Or is space an empty 'stage' in which all of the above exist?
...
- 11.7k
2
votes
1
answer
488
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 ...
- 11.7k
0
votes
2
answers
259
views
Don't rulers expand at the same rate as the universe they measure? [duplicate]
If you placed a giant ruler between the sun and our nearest star for example, wouldn't the divisions on the ruler expand at the same rate as the universe - therefore maintaining a constant distance? ...
- 7
0
votes
1
answer
59
views
Space is expanding but the space around me isn't [duplicate]
Everyone says space is expanding and distances between galaxies growing. But space isn't limited to outside of the earth. Space is everywhere on earth and around me. However I don't notice any ...
- 101
1
vote
1
answer
652
views
Why does dark energy seem to push things apart? [duplicate]
Ordinary matter acts to slow down the expansion of the universe. That makes intuitive sense, because the matter is exerting a gravitational force, acting to pull things together.
Moreover, dark ...
3
votes
3
answers
2k
views
Does our universe have an even distribution of matter in every direction
It occurred to me that it does since gravity in the space I exist appears to be uniform Ie there is no net movement of objects I observe in a particular direction. I maybe speaking from classical ...
- 101
1
vote
1
answer
332
views
What is the identity of Dark Matter?
What is the identity of dark matter?
Is it a particle?
Is it the lightest superpartner (LSP)?
Do the phenomena attributed to dark matter point not to some form of matter but actually to an ...
- 659
3
votes
1
answer
567
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 ...
23
votes
1
answer
9k
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 ...
- 3,241
5
votes
3
answers
2k
views
Creation of matter in the Big Bang
I appreciate your patience to my neophyte question. I am working on my dissertation in philosophy (which has nothing or little to do with physics) about the "problem of naming." Briefly what ...
- 59
194
votes
15
answers
31k
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 ...
- 2,055
50
votes
8
answers
7k
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 ...
- 603