How can we observe and measure interacting vacuum?

In summary, the conversation discusses the concept of vacuum state and its relation to matter and radiation fields in QFT. It is argued that while the absence of matter particles in a volume of space may imply the absence of on-shell photons, it does not necessarily mean the absence of all photons. The difference between an empty space and an interacting vacuum is explained in terms of energy scales, with the latter being much smaller than the former. It is also mentioned that in order to measure the value of interacting vacuum energy, radiation such as the CMB must be subtracted from the total energy of empty cosmic space.
  • #1
victorvmotti
155
5
When studying the QFT, one considers the vacuum state when the field is not excited and therefore no particles are present.

Now for the matter fields this makes sense to me. But what about the radiation field? Suppose we have an arbitrary small volume of space in the universe without any matter particles inside of it. An empty volume of space. But can we say that there are not any photons inside this empty volume?

I mean regardless of where we pick the empty of matter volume in the universe there is some radiation coming to that volume from some galaxy source. Then what is actually the difference between an empty (of matter) space and the interacting vacuum, an empty of on-shell matter and radiation space, that is talked about in the QFT.

I suppose by QFT vacuum we actually mean even there is no excitation of the electromagnetic field and therefore no on-shell photons. But can we have any volume of space at any time through which a real (not virtual) photon doesn't pass?

How can we observe and measure interacting vacuum value when we don't have a cosmic vacuum?

I guess that the answer is:

Because the distance scales that we talk about and calculate in interacting vacuum and vacuum energy in QFT is much much smaller, like 1/1000 of the proton radius, than the distance scales relevant for the cosmic vacuum and the thermal effects energy like CMB, right?

Actually we subtract all the radiation including the CMB from the energy inside of empty cosmic space to obtain experimental data on the value of interacting vacuum energy and compare with the QFT prediction, right?
 
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  • #2
For space filled with CMB, I think its energy is ##E=E_{vac}+E_{CMB}## with vacuum energy as default.
 

Related to How can we observe and measure interacting vacuum?

1. How is the vacuum defined in science?

The vacuum is defined as a space devoid of any matter or particles. It is also known as a region with a pressure lower than atmospheric pressure.

2. What are the different methods for observing and measuring the vacuum?

There are various methods for observing and measuring the vacuum, including pressure gauges, ion gauges, and residual gas analyzers. Other techniques such as optical interferometry and laser spectroscopy can also be used.

3. How can we measure the pressure of a vacuum?

The pressure of a vacuum can be measured using a device called a vacuum gauge. This device uses different principles such as thermal conductivity, ionization, and capacitance to determine the pressure of the vacuum.

4. What is the role of interactions in vacuum measurements?

Interactions play a crucial role in vacuum measurements as they can affect the pressure and composition of the vacuum. For example, interactions between particles and surfaces can lead to outgassing, which can impact the pressure of the vacuum.

5. How do scientists ensure accurate and precise measurements of the vacuum?

To ensure accurate and precise measurements of the vacuum, scientists use calibrated equipment and follow standardized procedures. They also take into account factors such as temperature, humidity, and the effects of interactions to minimize errors in their measurements.

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