<p>The answer given in the physics stackexchange to <a href="https://physics.stackexchange.com/questions/341669/virtual-particle-density-in-an-expanding-universe#:%7E:text=Anyway%2C%20since%20virtual%20particles%20don,changes%20as%20the%20universe%20expands.">a question about the density of virtual particles and references therein</a> is that virtual particles don't really exist, have no density, and therefore no mass density and do not contribute to the energy-density tensor.  Virtual particles are just a computational device that simplify the use of Feynman diagrams in order to get the final numbers that will predict a measurable value for some interaction.  They exist only in the popular science descriptions of quantum mechanics.
My evidence for this argument is that a series of answers along this vein have in excess of 40 upvotes from the physics fans.</p>

CC BY-SA 4.0
2022-07-09T01:12:41.843Z
2022-07-09T01:12:41.843Z
eshaya
<p>I know this is actually a physics question, but I can't ask anything there anymore and the same problem walks on my side on other forums... So, I take my chance to ask it here.</p>
<p>A virtual particle is off-shell (i.e., <span class="math-container">$E^2-p^2=m^2$</span> doesn't apply). That means that we can assign it an <span class="math-container">$E$</span> and <span class="math-container">$p$</span> independently from one another (which is ideal for interactions, as they can deliver the <span class="math-container">$E$</span> and <span class="math-container">$p$</span> needed for external real particles). So if a virtual particle has zero energy and non-zero momentum, the mass is imaginary, and it's square negative. This seems to imply negative gravity.</p>
<p>I'm aware that virtual particles are called virtual for good reason (I mean, how on Earth can a particle have zero energy and non-zero momentum, but the laws of QFT are just as strange as those of QM). They have an influence though, and if they can influence real particles, which can be seen to couple to the virtual field, you can envision the vacuum filled with quantum bubbles, virtual loops.</p>
<p>So maybe they are not real (you can't observe them) but they no doubt have influence. Or not? The quantum vacuum is different from classical empty space. It's naturally expanding. So maybe this virtual turmoil (quantum foam) is the cause.</p>

CC BY-SA 4.0
2022-06-28T13:08:15.633Z
Virtual particles also don't contribute anything until they go unvirtual, right?  I fear you may be wandering into musings which are inconsistent with current physical models.
Carl Witthoft
CC BY-SA 4.0
2022-06-29T05:53:22.963Z
@CarlWitthoft Real particles couple to the virtual field, don't they?
Felicia
<expansion><dark-energy>
Can virtual particles with zero energy and non-zero momentum contribute to dark energy?
Felicia
# Can virtual particles with zero energy and non-zero momentum contribute to dark energy?

(Asked by: username_0 on 2022-06-25)

I know this is actually a physics question, but I can't ask anything there anymore and the same problem walks on my side on other forums... So, I take my chance to ask it here.

A virtual particle is off-shell (i.e., $E^2-p^2=m^2$ doesn't apply). That means that we can assign it an $E$ and $p$ independently from one another (which is ideal for interactions, as they can deliver the $E$ and $p$ needed for external real particles). So if a virtual particle has zero energy and non-zero momentum, the mass is imaginary, and it's square negative. This seems to imply negative gravity.

I'm aware that virtual particles are called virtual for good reason (I mean, how on Earth can a particle have zero energy and non-zero momentum, but the laws of QFT are just as strange as those of QM). They have an influence though, and if they can influence real particles, which can be seen to couple to the virtual field, you can envision the vacuum filled with quantum bubbles, virtual loops.

So maybe they are not real (you can't observe them) but they no doubt have influence. Or not? The quantum vacuum is different from classical empty space. It's naturally expanding. So maybe this virtual turmoil (quantum foam) is the cause.

**Tags:** expansion, dark-energy
> **Comments:**
> **username_1**: Virtual particles also don't contribute anything until they go unvirtual, right?  I fear you may be wandering into musings which are inconsistent with current physical models.  
> **username_0**: @CarlWitthoft Real particles couple to the virtual field, don't they?  

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## 1 answers

### Answer by username_2 on 2022-07-09. Score: 1

The answer given in the physics stackexchange to [a question about the density of virtual particles and references therein](https://physics.stackexchange.com/questions/341669/virtual-particle-density-in-an-expanding-universe#:%7E:text=Anyway%2C%20since%20virtual%20particles%20don,changes%20as%20the%20universe%20expands.) is that virtual particles don't really exist, have no density, and therefore no mass density and do not contribute to the energy-density tensor. Virtual particles are just a computational device that simplify the use of Feynman diagrams in order to get the final numbers that will predict a measurable value for some interaction. They exist only in the popular science descriptions of quantum mechanics.
My evidence for this argument is that a series of answers along this vein have in excess of 40 upvotes from the physics fans.


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