Dark Energy: Observer Dependent or Absolute Rest Frame?

In summary, the cosmological constant in the Einstein field equations is a scalar that is independent of frame. However, it is sometimes described as a vacuum energy density, which may be frame dependent. However, the equations require that the vacuum energy density is always combined with a negative vacuum pressure density, ensuring Lorentz invariance.
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Khashishi
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If yes, does dark energy define a frame of absolute rest?

In the Einstein field equations, the cosmological constant is just a scalar, so it is independent of frame. But, sometimes, the cosmological constant is described as being a kind of vacuum energy density. Wouldn't a vacuum energy density be frame dependent? Or is it assumed that the vacuum energy density is always combined with a negative vacuum pressure density which cancels out the frame dependence?
 
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No. Dark energy is Lorentz invariant, whether you view it as a cosmological constant or as a vacuum energy density, since both appear the same way in the GR equations.

Khashishi said:
is it assumed that the vacuum energy density is always combined with a negative vacuum pressure density which cancels out the frame dependence?

It's not "assumed"; it's required by the equations. Dark energy (whether it's a cosmological constant or a vacuum energy density) appears in the equations as a constant that multiplies the metric; that means that in any local inertial frame, it looks like a positive energy density and an isotropic negative pressure that both have the same magnitude.
 
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1. What is dark energy?

Dark energy is a theoretical form of energy that is believed to make up about 70% of the universe. It is thought to be responsible for the accelerated expansion of the universe.

2. Is dark energy observer dependent or does it exist in an absolute rest frame?

This is a hotly debated topic in the scientific community. Some scientists believe that dark energy is dependent on the observer's frame of reference, while others argue that it exists in an absolute rest frame.

3. How do we detect or measure dark energy?

Dark energy cannot be directly observed or measured. Instead, scientists study its effects on the expansion of the universe through observations of distant galaxies and the cosmic microwave background radiation.

4. What is the difference between dark energy and dark matter?

Dark matter and dark energy are two different concepts. Dark matter is a type of matter that does not emit or interact with light, while dark energy is a form of energy that is thought to be responsible for the accelerated expansion of the universe.

5. What are the current theories about the origin of dark energy?

There are several theories about the origin of dark energy, but the most widely accepted one is the cosmological constant theory, which suggests that dark energy is a property of space itself. Other theories include the quintessence theory, which proposes that dark energy is a dynamic field, and the modified gravity theory, which suggests that gravity behaves differently on large scales.

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