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Calculating kinetic energy of all matterby jimjohnson
Tags: kinetic energy 
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#1
Jan2912, 09:59 AM

P: 84

Have there been estimates for the kinetic energy of all matter in the universe? For example, the Virgo supercluster moving at 700 km/sec though space has a kinetic energy of e62 erg. And of course, there is considerable movement of stars and matter within the cluster, just about everything has a velocity. The result has to be a large number. How close would it be to the energy equivalent of mass?



#2
Jan2912, 10:44 AM

P: 1,261

I'm not aware of any published material (and I kind of doubt there is any), but many cosmologists and high energy physicists are starting to think that the total energy of the universe is just about zeroi.e. all positive energy (e.g. kinetic, mass, etc) is balanced by negative (potential).
One thing to keep in mind is that your question doesn't have a trivial solution: (1) kinetic energy is referenceframe dependent (but it should be roughly equivalent for all inertial reference frames), (2) the way to treat kinetic energy from cosmological velocities (i.e. the hubble flow) isn't entirely clear, and (3) the velocity distribution of dark matter (which dominated mass by almost a factor of 10) isn't well constrained. 


#3
Jan2912, 10:57 AM

P: 84

I assume the negative energy is gravity which can be unlimited, right? Also,I was thinking in trivial terms, using assumptions to simlify the calculation but there was no overall purpose in mind. Thanks for the specific response.



#4
Jan2912, 03:50 PM

P: 38

Calculating kinetic energy of all matter
What wouldbethe point?



#5
Jan2912, 11:13 PM

P: 1,261

[itex] KE = \frac{1}{2} m v^2[/itex] and for cosmological hubble flow [itex] v = H_0 x[/itex] for the hubble constant [itex]H_0[/itex] and a distance x. Therefore: [tex] KE \approx \int M(x) (H_0 x)^2 dx [/tex] where M(x) is the mass function in terms of distance. ... Its definitely a nontrivial calculation ;) 


#6
Jan3012, 02:49 AM

Mentor
P: 16,192

You're calculating a framedependent quantity. So there is no unique answer.



#7
Jan3012, 08:02 AM

P: 84




#8
Jan3012, 08:19 AM

P: 84




#9
Jan3012, 11:26 AM

P: 518

Why not kinetic energy relative to the local cosmological rest frame? The frame where one is at rest with respect to the Cosmic Microwave Background.
This is because when we talk about motion, we usually talk about motion with respect to the local environment. When it is ambiguous, we then specify which environment it is relative to, like airspeed vs. groundspeed. 


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