Post by: geordief on 12/10/2022 15:18:13
Would I be right to suspect that these fields arose in the earliest epoch of the known universe?
Could the particles have "precitated" out of these fields as the fields expanded?(are they an integral if emergent phenomenon attributed to those fields?)
Or could it be that the expansion of the fields, allied to an asymmetry in them led to "eddies" that came to manifest themselves as particles (excitations)?
Is this perhaps something that is not yet known?
Post by: paul cotter on 12/10/2022 18:58:25
Post by: Eternal Student on 12/10/2022 19:04:10
Is this perhaps something that is not yet known?
At the very least, the answers are not well known to me. I don't claim to be an expert in QFT but I can write something about what little I know and hope that helps.
Would I be right to suspect that these fields (the fields of QFT) arose in the earliest epoch of the known universe?Possibly. These fundamental fields are assumed to exist throughout all of space and at all times. So it's not as if there was some time when the fields weren't there. To say it another way, these fields didn't appear or come into existence in some gradual or smooth way. If some space and time existed then the fields were also there, even if they had precisely 0 value everywhere.
So ,in QFT I hear that particles are excitations of their various fields.Yes, that's the correct idea.
Could the particles have "precitated" out of these fields as the fields expanded?(are they an integral if emergent phenomenon attributed to those fields?)Answer: Maybe. QFT is not usually done in concert with General Relativity. To say this another way, the background space is not assumed to have curvature, expansion as described by some scale factor a(t) in GR (General Relativity) or any of the properties that are common place in GR. More generally there remains difficulties uniting most Quantum theories with General relativity ( people often say "with gravity" instead of "with GR").
"Hawking Radiation" is one of the few examples where a result was obtained while assuming that QFT was operating on a background of curved space (the vicinity of a black hole). This wasn't a full unification of Quantum theory and GR but just a "work-around" that suggested one result in this very specific situation.
Anyway, what I'm trying to say is that while I know what it means for space to expand, it's not clear what meaning (if any) it has to suggest that the fundamental Quantum fields are expanding.
What is a more common explanation for the appearance of particles?
In QFT there are mechanisms for transferring energy from one fundamental field to another. So we really only need to find one field with some energy at an initial time and then it is possible for this energy to be transferred to a fundamental particle field (e.g. the electron field) at some later time. To say that another way, an electron can appear at a later time provided some other field has energy initially. There are several models of Cosmology but most of them will include inflation. This means the existance of an "inflaton field" in QFT. So, straight off the bat, we have one contender for an energetic Quantum Field at the big bang. Inflation would have been "on" and the inflaton field should have been at a high energy level. When the inflaton field fell to a lower level (when inflation was switched off) this energy can be transferred to other fundamental particle fields. As you mentioned earlier, particles are just excitations in their corresponding field: Hence, ordinary particles like electrons can start to appear when inflation stops.
I am NOT saying that all the energy we need for the particles that exist in our universe was originally in the inflaton field. There could very well be energy in various fields. It's just that the inflaton field is one obvious contender for an energetic field at early times (the big bang) which can then transfer energy to the other fundamental particle fields.
Best Wishes.
LATE EDITING: Fixed some spelling errors: Inflation (with an i ) is the process. Inflaton (without an i) is the particle or name of the field associated with inflation.
Post by: Halc on 13/10/2022 02:10:01
I've seen discussion of how there were not distinct fields at first, and gravity separated out first, followed by other forces/fields. This seems to suggest them 'arising' as geordief puts it. There was no distince space/time at the big bang. These things also arose. I don't think there are good answers to these sorts of questions without a unified field theory.Would I be right to suspect that these fields (the fields of QFT) arose in the earliest epoch of the known universe?Possibly. These fundamental fields are assumed to exist throughout all of space and at all times. So it's not as if there was some time when the fields weren't there.
Could the particles have "precitated" out of these fields as the fields expanded?(are they an integral if emergent phenomenon attributed to those fields?)A description of this is interpretation dependent. One could say that a specific excitation of some field is a valid solution to the wave function of the region in question. A collapse interpretation would probably require a measurement being made by something for the field to collapse into this particular particle.
Quote from: Eternal Studen
Inflaton (without an i) is the particle or name of the field associated with inflation.OK, that I didn't know.
Post by: Eternal Student on 14/10/2022 00:38:02
I've seen discussion of how there were not distinct fields at first, and gravity separated out first, followed by other forces/fields.Yes, that's OK. I've seen similar discussions, usually focusing on the fundamental forces and when they begin to separate as temperature and presure falls in the universe.
I had the impression that all the fundamental forces were always there, it's just that some were indistinguishable. To say this another way, the original one big force was always four individual forces added together but they all behaved the same way. So, there was in effect just the one big unified force. This is different from saying that some forces were not there at all. This could be a matter of semantics or personal preference but since it's a quiet day, I'm going to keep pushing the point.
Example: You have a stack of 4 bricks on top of each other, this height or the total stack is the value of the original grand unified force. Later on the bricks cool down and you can start to see that there are differences between the bricks: The yellow ones are water-proof, the red ones are harder, the green ones are spongy. That's how I imagine the situation: All the forces were always there, you just couldn't distinguish between them.
To put this on a more secure mathematical footing: There should be one Lagrangian describing the system (the whole universe), the one commonly used for the standard model of physics as derived from QFT is shown on this t-shirt:
Lagrangian tee.png (184.14 kB . 428x411 - viewed 1910 times)(The details aren't important AND indeed this is still thought to be just an approximation. It's a low energy approximation - a good approximation for the Lagrangian at sensible temperatures etc.)
Note that the standard model Lagrangian is just the sum of components, where each component is usually identified as being due to ... a photon field component, Higgs components,.... etc. etc.
Anyway, assuming the universe can be described with a Lagrangian then there is no reason why the Lagrangian would suddenly be thrown away and a different Lagrangian used at high temperatures or pressures such as close to the time of the big bang. However, many of the terms within each component can and do conceal expressions like (1/T) where T is the temperature. So as T ---> hot then these terms -->0. The disappearance of these terms results in the properties of what was the electromagnetic field becoming indistinguishable from those for the nuclear Weak force etc. Anyway, that's my take on it. The Lagrangian can't suddenly be a different Lagrangian at early times, it should really be just the one Lagrangian all the time. Just because you can't easily identify one component from another at high temperatures does not mean that they were not there, they were just a portion or fraction of the force you can find. (This is very informal, with many simplifications, for example not all the interactions or forces have a simple numerical value which you can just divide up into fractions, some interactions are described with rank n tensors instead of single numerical values).
Best Wishes.