How to determine the total energy in the universe

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Discussion Overview

The discussion centers around the determination of the total energy contained in the universe, exploring various theoretical frameworks and calculations related to energy content, including matter, dark matter, and dark energy. Participants engage with concepts from cosmology and the Lambda-CDM model, addressing both observable and theoretical aspects of the universe's energy.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants note that the total energy content of the universe is not definitively known, with some physicists suggesting it could be zero due to the cancellation of positive energy by negative gravitational energy.
  • One participant proposes calculating the energy content of matter in the observable universe by estimating the number of baryons and their energy content, leading to a rough estimate of ~10^89 eV.
  • Another participant simplifies the question to focus on the total rest energy of matter in the observable universe, providing a formula based on critical density and the Hubble constant, yielding an estimate of about 10^71 joules.
  • Further contributions clarify the breakdown of energy into components, with one participant stating that 25% of the universe's energy is matter, while 75% is attributed to dark energy.
  • Another participant provides a detailed mathematical derivation of the total mass-energy equivalence based on Lambda-CDM model parameters, arriving at a total energy estimate of approximately 9.419 x 10^71 joules.
  • There is a discussion about the classification of matter into dark matter and baryonic matter, with some participants emphasizing the importance of these distinctions in energy calculations.

Areas of Agreement / Disagreement

Participants express varying views on the total energy of the universe, with no consensus reached. Some agree on the framework of using the Lambda-CDM model for calculations, while others highlight the uncertainty surrounding the total energy concept itself.

Contextual Notes

The discussion involves assumptions about the universe's density, the classification of energy components, and the extent of the observable universe, which may affect the calculations presented. The reliance on specific cosmological parameters and definitions introduces additional complexity and potential for differing interpretations.

Who May Find This Useful

This discussion may be of interest to those studying cosmology, astrophysics, or related fields, particularly individuals looking to understand the complexities involved in calculating the total energy of the universe and the implications of different energy components.

Tipi
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How to determine the total energy of matter in the universe

Hi all,

while looking at a table of order of magnitudes of energies in nature, I just realize that I really don't know how to determine the total energy contained in the universe (near 10 to the 69).

Can someone get this number with a simple argument?

Thanks a lot,

TP
 
Last edited:
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It's not known. Many physicist believe (Feynman was one of them) that the total energy content of the universe is exactly zero, with the positive energy of the matter in the universe being exactly canceled by the negative energy of the gravitational field.
 


phyzguy said:
It's not known. Many physicist believe (Feynman was one of them) that the total energy content of the universe is exactly zero, with the positive energy of the matter in the universe being exactly canceled by the negative energy of the gravitational field.

Ok. That was not the answer I was looking for but it's interesting.

So, how could we determine the positive energy of matter, for instance?

Thanks,

TP

[edit] Enhanced title...
 
Well, we don't know the extent of the universe, or even whether it is finite or infinite. You could calculate the energy content of the matter in the observable universe by adding up all of the mass and multiplying by c^2. The observable universe has been estimated (http://en.wikipedia.org/wiki/Observable_universe) to contain about 10^80 baryons, so, since a proton has an energy content of about 2 GeV, you could estimate a baryon energy content of ~10^89 eV. Then there is the dark matter...
 
The total energy in the universe is a vague concept that might not have a well-defined answer. So let's simplify your question to "what is the total rest energy of all the matter in the observable universe?". This is easier to answer now.

Some assumptions (ask if you need elaboration on any of them): The universe is at the critical density, and matter makes up 25% of the universe. The Hubble constant today is 72km/s/Mpc. The observable universe is 46 billion light years in radius.

We can then get the total energy, as we've defined it, as
E = \frac{1}{4}\rho\,c^2\,V
E = \frac{1}{4}\frac{3H_0^2c^2}{8\pi\,G}\frac{4\pi}{3}R^3

If we put in the numbers, we get about 10^71 joules.
 
nicksauce said:
The total energy in the universe is a vague concept that might not have a well-defined answer. So let's simplify your question to "what is the total rest energy of all the matter in the observable universe?". This is easier to answer now.

Some assumptions (ask if you need elaboration on any of them): The universe is at the critical density, and matter makes up 25% of the universe. The Hubble constant today is 72km/s/Mpc. The observable universe is 46 billion light years in radius.

We can then get the total energy, as we've defined it, as
E = \frac{1}{4}\rho\,c^2\,V
E = \frac{1}{4}\frac{3H_0^2c^2}{8\pi\,G}\frac{4\pi}{3}R^3

If we put in the numbers, we get about 10^71 joules.

Thanks for your answer. Could you explain a little were the first equation come from and how you go to the second?

Thanks,

TP

[edit] OK. I get the first one, I didnt saw its evidence on first look. And for the second one, you used H_\text{crit} =30\sqrt (\rho (m_p/m^3))?
 
Last edited:
Energy = (1/4 of energy is matter) * energy density * volume

I used 1/4 of energy is matter because the universe is thought to be roughly 75% dark energy, and 25% matter, where the 25% matter can be further decomposed into dark matter and dark energy.

Then I used that
\rho_{crit} = \frac{3H_0^2}{8\pi\,G}
 
I think nicksauce meant the 25% of matter can be further classified by two groups, dark matter and Intergalactic Dust/Stars, just a clarification.
 
Agreed, dark energy is part of the 'missing' ~75% energy component. This makes perfect sense for reasons involving a lot of weird math.
 
  • #10
Kevin_Axion said:
I think nicksauce meant the 25% of matter can be further classified by two groups, dark matter and Intergalactic Dust/Stars, just a clarification.

Errr yes. Of course.
 
  • #11
Total amount of energy in the Universe...

Tipi said:
while looking at a table of order of magnitudes of energies in nature, I just realize that I really don't know how to determine the total energy contained in the universe (near 10 to the 69).

Can someone get this number with a simple argument?

Affirmative.

These are my equations for the total Universe_mass-energy equivalence based upon the Lambda-CDM model parameters and the Hubble Space Telescope (HST) and WMAP observational parameters and the Hubble radius in Systeme International units.

H_0 = 2.3298 \cdot 10^{- 18} \; \text{s}^{- 1} - Hubble parameter (WMAP)
\Omega_s = 0.005 - Lambda-CDM stellar Baryon density parameter
dN_s = 10^{22} - Hubble Space Telescope observable stellar number
dV_s = 3.3871 \cdot 10^{78} \; \text{m}^3 \; \; \; (4 \cdot 10^{30} \; \text{ly}^3) - Hubble Space Telescope observable stellar volume
M_{\odot} = 1.9891 \cdot 10^{30} \; \text{kg} - solar mass

Hubble Space Telescope observable stellar density:
\rho_s = M_{\odot} \left( \frac{dN_s}{dV_s} \right)

Hubble radius:
R_0 = \frac{c}{H_0}

Hubble sphere volume:
V_0 = \frac{4 \pi R_0^3}{3} = \frac{4 \pi}{3} \left( \frac{c}{H_0} \right)^3

Observable Universe_mass-energy equivalence total mass integration by substitution:
M_t = \frac{\rho_s V_0}{\Omega_s} = \frac{4 \pi M_{\odot}}{3 \Omega_s} \left( \frac{dN_s}{dV_s} \right) \left( \frac{c}{H_0} \right)^3 = 1.048 \cdot 10^{55} \; \text{kg}

Observable Universe_mass-energy equivalence total mass
\boxed{M_t = \frac{4 \pi M_{\odot}}{3 \Omega_s} \left( \frac{dN_s}{dV_s} \right) \left( \frac{c}{H_0} \right)^3}

\boxed{M_t = 1.048 \cdot 10^{55} \; \text{kg}}

However, only a fraction of this total mass exists in the form of mass in the Universe, which is composed of 22.8% cold dark matter and 4.56% ordinary baryonic matter.

\Omega_m = \Omega_{c} + \Omega_b = 0.2736 - Lambda-CDM total matter density

Universe total matter mass integration by substitution:
M_u = \Omega_m M_t = \frac{4 \pi M_{\odot}}{3} \left( \frac{\Omega_m}{\Omega_s} \right) \left( \frac{dN_s}{dV_s} \right) \left( \frac{c}{H_0} \right)^3 = 2.867 \cdot 10^{54} \; \text{kg}

Universe total matter mass:
\boxed{M_u = \frac{4 \pi M_{\odot}}{3} \left( \frac{\Omega_m}{\Omega_s} \right) \left( \frac{dN_s}{dV_s} \right) \left( \frac{c}{H_0} \right)^3}

Universe total matter mass:
\boxed{M_u = 2.867 \cdot 10^{54} \; \text{kg}}

Universe_mass-energy equivalence integration by substitution:
E_t = M_t c^2 = \left[ \frac{4 \pi M_{\odot}}{3 \Omega_s} \left( \frac{dN_s}{dV_s} \right) \left( \frac{c}{H_0} \right)^3 \right] c^2 = \frac{4 \pi c^5 M_{\odot}}{3 \Omega_s H_0^3} \left( \frac{dN_s}{dV_s} \right) = 9.419 \cdot 10^{71} \; \text{j}

Universe_mass-energy equivalence total energy:
\boxed{E_t = \frac{4 \pi c^5 M_{\odot}}{3 \Omega_s H_0^3} \left( \frac{dN_s}{dV_s} \right)}

Total amount of energy in the Universe:
\boxed{E_t = 9.419 \cdot 10^{71} \; \text{j}}

However, only a fraction of this total energy exists in the form of energy in the Universe, which is composed of dark energy at 72.6%.

\Omega_{\Lambda} = 0.726 - Lambda-CDM dark energy density

Total amount of dark energy in the Universe integration by substitution::
E_{\Lambda} = \Omega_{\Lambda} E_t = \frac{4 \pi c^5 M_{\odot}}{3 H_0^3} \left( \frac{\Omega_{\Lambda}}{\Omega_s} \right) \left( \frac{dN_s}{dV_s} \right) = 6.838 \cdot 10^{71} \; \text{j}

Universe dark energy total energy:
\boxed{E_{\Lambda} = \frac{4 \pi c^5 M_{\odot}}{3 H_0^3} \left( \frac{\Omega_{\Lambda}}{\Omega_s} \right) \left( \frac{dN_s}{dV_s} \right)}

Total amount of dark energy in the Universe:
\boxed{E_{\Lambda} = 6.838 \cdot 10^{71} \; \text{j}}
[/Color]
Reference:
http://en.wikipedia.org/wiki/Hubble%27s_law"
http://en.wikipedia.org/wiki/Lambda-CDM_model"
http://en.wikipedia.org/wiki/Universe"
http://en.wikipedia.org/wiki/Observable_universe"
http://en.wikipedia.org/wiki/Hubble's_law#Interpretation"
http://en.wikipedia.org/wiki/Hubble_volume"
http://en.wikipedia.org/wiki/Dark_matter"
http://en.wikipedia.org/wiki/Dark_energy"
 
Last edited by a moderator:
  • #12
Excellent, response.
 
  • #13
Total amount of energy in the Universe...


800px-2MASS_LSS_chart-NEW_Nasa.jpg

The distribution of galaxies beyond the Milky Way.

Hubble radius:
R_0 = \frac{c}{H_0}

\boxed{R_0 = 1.286 \cdot 10^{26} \; \text{m}}

However, the present observable Universe radius exceeds the Hubble radius due to cosmic inflation:
\boxed{R_u \geq R_0}

R_u = 3.419 \cdot R_0 = \frac{3.419 c}{H_0} = 4.399 \cdot 10^{26} \; \text{m} \; \; \; (46.5 \cdot 10^9 \; \text{ly})

Universe observable radius:
\boxed{R_u = 4.399 \cdot 10^{26} \; \text{m}}

Hubble critical density:
\rho_c = \frac{3 H_0^2}{8 \pi G}

Universe sphere volume:
V_u = \frac{4 \pi R_u^3}{3}

For the post #5 equation for the Universe total energy integration by substitution:
E_t = \rho_c c^2 V_u = \frac{4 \pi c^2}{3} \left( \frac{3 H_0^2}{8 \pi G} \right) R_u^3 = \frac{H_0^2 c^2 R_u^3}{2 G} = 3.112 \cdot 10^{71} \; \text{j}

\boxed{E_t = \frac{H_0^2 c^2 R_u^3}{2 G}}

\boxed{E_t = 3.112 \cdot 10^{71} \; \text{j}}

These are my equations for the total Universe_mass-energy equivalence based upon the Lambda-CDM model parameters and the Hubble Space Telescope (HST) and WMAP observational parameters and the observable Universe radius in Systeme International units.

R_u = 4.399 \cdot 10^{26} \; \text{m} - observable Universe radius
H_0 = 2.3298 \cdot 10^{- 18} \; \text{s}^{- 1} - Hubble parameter (WMAP)
\Omega_s = 0.005 - Lambda-CDM stellar Baryon density parameter
dN_s = 10^{22} - Hubble Space Telescope observable stellar number
dV_s = 3.3871 \cdot 10^{78} \; \text{m}^3 \; \; \; (4 \cdot 10^{30} \; \text{ly}^3) - Hubble Space Telescope observable stellar volume
M_{\odot} = 1.9891 \cdot 10^{30} \; \text{kg} - solar mass

Hubble Space Telescope observable stellar density:
\rho_s = M_{\odot} \left( \frac{dN_s}{dV_s} \right)

Universe observable radius:
\boxed{R_u = 4.399 \cdot 10^{26} \; \text{m}}

Universe sphere volume:
V_u = \frac{4 \pi R_u^3}{3}

Observable Universe_mass-energy equivalence total mass integration by substitution:
M_t = \frac{\rho_s V_u}{\Omega_s} = \frac{4 \pi M_{\odot}}{3 \Omega_s} \left( \frac{dN_s}{dV_s} \right) R_u^3 = 4.188 \cdot 10^{56} \; \text{kg}

Observable Universe_mass-energy equivalence total mass
\boxed{M_t = \frac{4 \pi M_{\odot}}{3 \Omega_s} \left( \frac{dN_s}{dV_s} \right) R_u^3}

\boxed{M_t = 4.188 \cdot 10^{56} \; \text{kg}}

However, only a fraction of this total mass exists in the form of mass in the Universe, which is composed of 22.8% cold dark matter and 4.56% ordinary baryonic matter.

\Omega_m = \Omega_{c} + \Omega_b = 0.2736 - Lambda-CDM total matter density

Universe total matter mass integration by substitution:
M_u = \Omega_m M_t = \frac{4 \pi M_{\odot}}{3} \left( \frac{\Omega_m}{\Omega_s} \right) \left( \frac{dN_s}{dV_s} \right) R_u^3 = 1.146 \cdot 10^{56} \; \text{kg}

Universe total matter mass:
\boxed{M_u = \frac{4 \pi M_{\odot}}{3} \left( \frac{\Omega_m}{\Omega_s} \right) \left( \frac{dN_s}{dV_s} \right) R_u^3}

Universe total matter mass:
\boxed{M_u = 1.146 \cdot 10^{56} \; \text{kg}}

Universe_mass-energy equivalence integration by substitution:
E_t = M_t c^2 = \left[ \frac{4 \pi M_{\odot}}{3 \Omega_s} \left( \frac{dN_s}{dV_s} \right) R_u^3 \right] c^2 = \frac{4 \pi c^2 M_{\odot}}{3 \Omega_s} \left( \frac{dN_s}{dV_s} \right) R_u^3 = 3.764 \cdot 10^{73} \; \text{j}

Universe_mass-energy equivalence total energy:
\boxed{E_t = \frac{4 \pi c^2 M_{\odot}}{3 \Omega_s} \left( \frac{dN_s}{dV_s} \right) R_u^3}

Total amount of energy in the Universe:
\boxed{E_t = 3.764 \cdot 10^{73} \; \text{j}}

However, only a fraction of this total energy exists in the form of energy in the Universe, which is composed of dark energy at 72.6%.

\Omega_{\Lambda} = 0.726 - Lambda-CDM dark energy density

Total amount of dark energy in the Universe integration by substitution::
E_{\Lambda} = \Omega_{\Lambda} E_t = \frac{4 \pi c^2 M_{\odot}}{3} \left( \frac{\Omega_{\Lambda}}{\Omega_s} \right) \left( \frac{dN_s}{dV_s} \right) R_u^3 = 2.733 \cdot 10^{73} \; \text{j}

Universe dark energy total energy:
\boxed{E_{\Lambda} = \frac{4 \pi c^2 M_{\odot}}{3} \left( \frac{\Omega_{\Lambda}}{\Omega_s} \right) \left( \frac{dN_s}{dV_s} \right) R_u^3}

Total amount of dark energy in the Universe:
\boxed{E_{\Lambda} = 2.733 \cdot 10^{73} \; \text{j}}
[/Color]
Reference:
http://en.wikipedia.org/wiki/Hubble%27s_law"
http://en.wikipedia.org/wiki/Lambda-CDM_model"
http://en.wikipedia.org/wiki/Universe"
http://en.wikipedia.org/wiki/Observable_universe"
http://en.wikipedia.org/wiki/Dark_matter"
http://en.wikipedia.org/wiki/Dark_energy"
http://en.wikipedia.org/wiki/Hubble's_law#Interpretation"
http://en.wikipedia.org/wiki/Hubble_volume"
http://en.wikipedia.org/wiki/Friedmann_equations#Density_parameter"
 
Last edited by a moderator:

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