B Why is vacuum energy assumed to be uniform?

[newjerseyrunner]

Considering that all energy gravitates, why is it assumed that the vacuum energy that we measure inside the gravity well of the Milky Way is consistent throughout space? Is there any real way to know? Would it make any difference in the problem that QM and GR differ in the vacuum energy density by many orders of magnitude?

 

[bhobba]

You mean the quantum field vacuum energy? Its zero by a process called normal ordering:
https://en.wikipedia.org/wiki/Normal_order

Thanks
Bill

 

[rootone]

why is it assumed that the vacuum energy that we measure inside the gravity well of the Milky Way is consistent throughout space?

Because so far there is no reason to think that it might be different

 

[Demystifier]

Considering that all energy gravitates, why is it assumed that the vacuum energy that we measure inside the gravity well of the Milky Way is consistent throughout space? Is there any real way to know?

That's a question for the Cosmology subform.
<Moderator's note: thread moved>

Would it make any difference in the problem that QM and GR differ in the vacuum energy density by many orders of magnitude?

Yes, if we believe that gravity should be quantized too.

 

[Chronos]

Blame it on Boltzmann, he's the wise guy who decided discrete values of things should follow a basic statistical distribution when gathered in sufficiently large numbers. In the case at hand it is entirely analogous and reasonable to think of vacuum energy as equivalent to the salinity of sea water. How much variance would you expect at various locations in the vast ocean of space? It has had billions of years to equalize.

 

[Chalnoth]

Considering that all energy gravitates, why is it assumed that the vacuum energy that we measure inside the gravity well of the Milky Way is consistent throughout space? Is there any real way to know? Would it make any difference in the problem that QM and GR differ in the vacuum energy density by many orders of magnitude?

We can't actually measure vacuum energy locally at all: its value (if non-zero) is far too small to detect directly. Our only evidence for the value of vacuum energy stems from Observations of galaxies and other structures many millions to billions of light years away.