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Why is there something instead of nothing?


Melthadora
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24 minutes ago, joigus said:

This is actually, IMO, an outstanding question, because I haven't the faintest idea how you would apply the principles of the quantum theory of measurement to the vacuum. I don't suppose you can do that. Certainly, as there were no real particles, only those ephemeral virtual states, how did something actually happen? Nothing would qualify as an observer or as an apparatus.

Decoherence is not it, IMO, because I don't know of any instance in which the vacuum can be argued to bring about decoherence and thereby qualifying as producing a measurement. This is a part of the quantum theory of measurement that's slipped into oblivion: the problem of the pointer positions. What physical tag says that something, and not something else, has actually happened? What tips the arrow?

If anybody knows of any answer to that I would be the first to thank them, because I've longed to know for more than 20 years. It was very frequently referred to in the old papers and books about measurement, but no longer is.

Is there any path where some of those combined virtual states don't annihilate and can become stable, measurable quanta? It must have happened because... here we are.

Edited by StringJunky
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Just now, StringJunky said:

 

Is there any path where those combined virtual states don't annihilate and can become stable, measurable quanta? It must have happened because... here we are.

Sure, but you have to provide the energy. That's what's happening when you hit a proton with an energetic particle. You put in the required energy for some of these virtual particles to persist. In the inflationary theory it's the inflaton field that provides that energy. But my next question would be: What's the status of the inflaton field? Is itself a quantized field, with quanta? Why wasn't it in a superposition of states when all that transition happened?

I think there are possible answers to that. For example, superselection rules, which are strict prohibitions for superpositions of different quantum numbers to exist. But the whole thing becomes more and more contrived... The inflaton field is acting like the physical element that defines the fate of these fluctuations.

It's kind of jerry-built. Successful, useful, very impressive to be sure, but it doesn't give you anything like this feeling of inevitability that you normally demand of fundamental theories. Like something remains to be understood.

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9 minutes ago, joigus said:

Sure, but you have to provide the energy. That's what's happening when you hit a proton with an energetic particle. You put in the required energy for some of these virtual particles to persist. In the inflationary theory it's the inflaton field that provides that energy. But my next question would be: What's the status of the inflaton field? Is itself a quantized field, with quanta? Why wasn't it in a superposition of states when all that transition happened?

I think there are possible answers to that. For example, superselection rules, which are strict prohibitions for superpositions of different quantum numbers to exist. But the whole thing becomes more and more contrived... The inflaton field is acting like the physical element that defines the fate of these fluctuations.

It's kind of jerry-built. Successful, useful, very impressive to be sure, but it doesn't give you anything like this feeling of inevitability that you normally demand of fundamental theories. Like something remains to be understood.

Thanks. I'm out of my depth now. :)

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The only inflationary models that make sense to me ( as there are quite a few ), are the ones that happen at about 10^-35 sec, long ( relatively ) after the Planck era.
Previous to this the universe was precariously balanced on a false zero vacuum energy. This unstable state resulted in a symmetry break ( electroweak ) and subsequent slow ( again relatively ) roll down to an actual ( ? ) zero vacuum energy. This energy difference provided for the exponential inflation of the universe until 10^-32 sec and gave mass to fermions through the Higgs mechanism.
Prior to this inflationary period the Universe was radiation dominated, IOW all particles were massless, but not just virtual, there were real particles also.

So you call it the inflaton field, I call it a vacuum energy step ( Mordred used to call it Mexican hat potential ), and so I have no problem with the vacuum potential being quantized ( as it is in the present era ).
We may actually still be in a very, very slow roll, and that would explain Dark Energy that drives accelerated expansion.

Edited by MigL
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12 hours ago, MigL said:

The only inflationary models that make sense to me ( as there are quite a few ), are the ones that happen at about 10^-35 sec, long ( relatively ) after the Planck era.
Previous to this the universe was precariously balanced on a false zero vacuum energy. This unstable state resulted in a symmetry break ( electroweak ) and subsequent slow ( again relatively ) roll down to an actual ( ? ) zero vacuum energy. This energy difference provided for the exponential inflation of the universe until 10^-32 sec and gave mass to fermions through the Higgs mechanism.
Prior to this inflationary period the Universe was radiation dominated, IOW all particles were massless, but not just virtual, there were real particles also.

So you call it the inflaton field, I call it a vacuum energy step ( Mordred used to call it Mexican hat potential ), and so I have no problem with the vacuum potential being quantized ( as it is in the present era ).
We may actually still be in a very, very slow roll, and that would explain Dark Energy that drives accelerated expansion.

But inflation corresponds to slow-roll down the hill, so that's previous to reheating, and thereby previous to plasma epoch, baryogenesis, radiation-dominated epoch and everything else. The super-stretching is always previous to big-bang cosmology.

And the inflaton looks nothing like a Higgs potential (Mexican hat). It's a completely different animal:

On 8/30/2020 at 7:02 PM, joigus said:

*"Model the curve correctly" means it must look something like this (take a look at the graph):

<image>

Although there are other models. But the parts of the graph that has received good confirmation is the part with a gentle slope and the steep fall.

The breaking of the symmetry that we commonly associate with the acquisition of mass came much later. After re-heating.

V(phi) is the potential and phi is the inflaton.

The V(phi) for the Higgs is very different:

higgspotential.png

Online lectures that I found very useful to understand how the inflaton is very different from other scalar fields are (Lenny Susskind, Stanford):

https://www.youtube.com/watch?v=gdFldkitkJA&list=PLvh0vlLitZ7c8Avsn6gUaWX05uD5cedO-&index=8

1h 15' 12'' to the end

And then:

https://www.youtube.com/watch?v=gdFldkitkJA&list=PLvh0vlLitZ7c8Avsn6gUaWX05uD5cedO-&index=8

The Higgs potential is a static situation. The inflaton dynamics, on the other hand, is analogous to the dynamics of a body falling under viscous drag. And the Hubble parameter plays the role of the friction.

 

Edited by joigus
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That image sure looks like a 'sombrero' to me :) ,

14 minutes ago, joigus said:

The breaking of the symmetry that we commonly associate with the acquisition of mass came much later. After re-heating.

unfortunately any symmetry break is a 'fall' from an unstable false potential to a lower ( more ) stable one.
This vacuum energy has to go somewhere, and usually it leads to an inflation.
I can't see the electroweak symmetry break not leading to an inflationary period.
And of course by radiation dominated, I mean only massless particles, so definitely before baryogenesis and the plasma era ( maybe I'm using the term 'radiation dominated' wrong ).
Those are some of the reasons why I say 'makes sense to me'.

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43 minutes ago, MigL said:

This vacuum energy has to go somewhere, and usually it leads to an inflation.

Good point about the Higgs. +1

But in the case of the Higgs the "inflation" is making massless particles gain weight. Higgs is like free-delivery pizza for all citizens.

The inflaton is rather like more elbow room for everybody. It affects the expansion parameter. Similar to free real estate for all citizens.

And there's always the question of who put the ball at the top of the hill? ;) The question of the initial conditions of the universe.

But you make a very interesting point there. If the "ball" (the state of the Higgs phi) started on top of the hill, it must have liberated kinetic energy. I don't see it as inflation of space, but as liberation of kinetic energy, and thereby heating. Maybe that's already contemplated by cosmologists. But it's a very good argument. Maybe @Mordred has an interesting answer to it when he comes back.

And radiation-dominated comes from the sequence of states after the big bang:

1) Universe opaque to radiation --> ending with decoupling of photons/charged particles

2) Energy density proportional to const./a (radiation dominated)

3) Energy density proportional to const./a3 (matter/dark matter dominated)

4) Energy density proportional to const. (vacuum dominated = the present epoch)

where a is the expansion parameter and the Hubble parameter would be,

\[H=\frac{\dot{a}}{a}\]

I think you're using it right.

Edited by joigus
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i can answer your question, nothingness is not impossible, take for example vacuum, it is a part of nothingness, it has no color, it pulls and sends away matter, it is not black, the blackness in the universe is only because of our eyes, our eyes and brain cannot perceive nothingness, our eyes are not designed to detect it, we have no sense of it, a blind person only knows black, not true nothingness, if our mind could perceive nothingness, it would not exist, again, nothingness

sorry if this is stupid or too... you know.. impossible

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3 minutes ago, AgentF2S said:

i can answer your question, nothingness is not impossible, take for example vacuum, it is a part of nothingness, it has no color, it pulls and sends away matter, it is not black, the blackness in the universe is only because of our eyes, our eyes and brain cannot perceive nothingness, our eyes are not designed to detect it, we have no sense of it, a blind person only knows black, not true nothingness, if our mind could perceive nothingness, it would not exist, again, nothingness

sorry if this is stupid or too... you know.. impossible

Quantum physics tells us a vacuum is not nothingness.

 

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1 hour ago, AgentF2S said:

i know this was stupid, thanks for mentioning tho

i did say it wasn't true nothingness 

It's not stupid, it's a matter of not having been exposed to the ideas yet. You learned something, which is a positive. 

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On 8/31/2020 at 5:38 PM, MigL said:

I think we had better first define a common meaning of "nothing'.

[ ... ] 

So the concept of 'absolute nothingness' becomes meaningless once QM is accounted for, as it can never exist.

 

On 8/31/2020 at 10:17 PM, joigus said:

[ ... ]

My phrasing of it would be, "there's always something."

 

4 hours ago, swansont said:

Quantum physics tells us a vacuum is not nothingness.

 

A photon travels at c in a vacuum.  Is this correct?

A photon slows below c when travelling through a medium.  Is this correct?

If both statements are correct, and if a vacuum is not nothingness, how do we know for sure that 186,282 mph is the upper speed limit of a photon?  Wouldn't the 'something' be slowing it down, even ever so slightly?


 

Edited by Dord
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A photon travels at c when passing through a medium with which it does not interact.
Photons tend to interact with a lot of things electromagnetically.
A neutrino, which has mass but interacts much less and only through the Weak ( short range ) interaction, often gets to its destination faster than photons emitted at the same time.

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3 hours ago, Dord said:

 

 

A photon travels at c in a vacuum.  Is this correct?

A photon slows below c when travelling through a medium.  Is this correct?

If both statements are correct, and if a vacuum is not nothingness, how do we know for sure that 186,282 mph is the upper speed limit of a photon?  Wouldn't the 'something' be slowing it down, even ever so slightly?


 

It is hypothesized that if you can reduce the energy of the vacuum with the Casimir effect, you could speed up photons by a tiny amount. Not a big enough effect to measure.

https://en.wikipedia.org/wiki/Scharnhorst_effect

A photon traveling between two plates that are 1 micrometer apart would increase the photon's speed by only about one part in 1036.

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9 hours ago, swansont said:

It is hypothesized that if you can reduce the energy of the vacuum with the Casimir effect, you could speed up photons by a tiny amount. Not a big enough effect to measure.

https://en.wikipedia.org/wiki/Scharnhorst_effect

A photon traveling between two plates that are 1 micrometer apart would increase the photon's speed by only about one part in 1036.

Interesting...I hadn’t heard of this one before :) 

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