lexico

04-03-05, 14:14

Is the universe infinite or finite ?

In volume, density, and mass ?

Let's talk about it !

Please add relevant comments and links; what you have below is just what was readily available on the web.

Credit: Douglas Scott (http://www.astro.ubc.ca/people/scott/)'s FAQ page (http://www.astro.ubc.ca/people/scott/faq_email.html)

Astronomy Group at University of British Columbia (http://www.astro.ubc.ca/people/)

According to the following passage, the dimensisions are;

RADIUS: ~10,000 Megaparsec or 3 ~ 10^26 metres

DENSITY: ~ 10^-26kg/m3

TOTAL MASS: ~ 10^54 kilogrammesQ: "Do you know where I can find an estimate of the total mass of the universe?"

Submitted by [email protected] 10/00

A: "From observations of the Universe it is possible to determine the average density. In other words the mass per unit volume (or the mass-energy equivalent per unit volume). Currently the mass-energy census of the Universe identifies at least 5 separate components: ordinary matter (baryons); massive neutrinos (a known, but ellusive particle, which may have a small mass); cold dark matter (some as yet unidentified particle); photons (mainly the CMB); and Dark Energy (which may dominate the census, even although it doesn't behave like matter at all!). It appears that the Universe has a "flat" geometry, so that =1, and estimates for the contributions from each of the 5 components are 5%, 0.3%, 30%, 0.01% and 65%, respectively.

Coverting into density requires having an estimate of how fast the Universe is expanding, i.e. the Hubble constant (since that goes into the definition of , as described in another answer). Using a typical value for H0 the overall density of the Universe turns out to be about 10-26kg/m3. This corresponds to about 1011 times the mass of the Sun in every cubic Megaparsec of volume. This value is uncertain both because the value of isn't precisely known, and also because the value of H0 isn't precisely known either. But it's certainly the correct order of magnitude. You'd also get a proportionately lower number if you wanted only the density in baryons, for example.

The total mass of the Universe, on the other hand, is not a very clear concept. The Universe is likely to be either infinite in volume, or so very large that it can be considered infinite for all practical purposes. That means that the total mass of the Universe is also infinite. The thing which can be well-defined though, is the mass within the observable part of the Universe. In other words we can ask: how much mass is contained within the volume that we can have observed since the Big Bang? The radius of the observable Universe is about 10,000 Megaparsec (or about 3 ~ 1026 metres). Using the above estimate for the total density this gives a total mass in the observable Universe of about 1054 kilogrammes. That's the best answer I can give for the mass of the Universe!"

According to the following passage,

RADIUS: ~ 300 Yotta meters or 3 x 10^26 m

DENSITY: ~10^-26kg/m3

TOTAL MASS: ~ 6 x 10^53 kilogrammes.Q: "Do you know where I can find an estimate of the total mass of the universe?"

Submitted by [email protected] 10/00

A: "If the Universe has "flat" or "open" geometry, then formally it has infinite volume, and therefore infinite mass. Something which is better defined is the mass within the "Observable Universe", which means the part of space from which we can have received light in the history of the Universe so far. This gets bigger every day!

The approximate answer is that the radius of the observable Universe is currently estimated to be about 300 Ym (that's "yotta-metres", or 10^24m, which is the largest SI prefix!). So you take that number, cube it, and multiply by 4/3, to get the volume of the whole sphere.

Then you have to decide what density you want to use. Are you only interested in luminous matter, or do you want to include all the baryons (regular stuff made of protons and neutrons)? Or do you want all the particle dark matter too? And what about the dark energy? If you include everything, then the average density in the Universe today is about 10-26kg/m3. And the mass in the observable Universe can be estimated accordingly.

There are several uncertainties and approximations here though - so don't expect your answer to be much better than an order of magnitude estimate!"

In volume, density, and mass ?

Let's talk about it !

Please add relevant comments and links; what you have below is just what was readily available on the web.

Credit: Douglas Scott (http://www.astro.ubc.ca/people/scott/)'s FAQ page (http://www.astro.ubc.ca/people/scott/faq_email.html)

Astronomy Group at University of British Columbia (http://www.astro.ubc.ca/people/)

According to the following passage, the dimensisions are;

RADIUS: ~10,000 Megaparsec or 3 ~ 10^26 metres

DENSITY: ~ 10^-26kg/m3

TOTAL MASS: ~ 10^54 kilogrammesQ: "Do you know where I can find an estimate of the total mass of the universe?"

Submitted by [email protected] 10/00

A: "From observations of the Universe it is possible to determine the average density. In other words the mass per unit volume (or the mass-energy equivalent per unit volume). Currently the mass-energy census of the Universe identifies at least 5 separate components: ordinary matter (baryons); massive neutrinos (a known, but ellusive particle, which may have a small mass); cold dark matter (some as yet unidentified particle); photons (mainly the CMB); and Dark Energy (which may dominate the census, even although it doesn't behave like matter at all!). It appears that the Universe has a "flat" geometry, so that =1, and estimates for the contributions from each of the 5 components are 5%, 0.3%, 30%, 0.01% and 65%, respectively.

Coverting into density requires having an estimate of how fast the Universe is expanding, i.e. the Hubble constant (since that goes into the definition of , as described in another answer). Using a typical value for H0 the overall density of the Universe turns out to be about 10-26kg/m3. This corresponds to about 1011 times the mass of the Sun in every cubic Megaparsec of volume. This value is uncertain both because the value of isn't precisely known, and also because the value of H0 isn't precisely known either. But it's certainly the correct order of magnitude. You'd also get a proportionately lower number if you wanted only the density in baryons, for example.

The total mass of the Universe, on the other hand, is not a very clear concept. The Universe is likely to be either infinite in volume, or so very large that it can be considered infinite for all practical purposes. That means that the total mass of the Universe is also infinite. The thing which can be well-defined though, is the mass within the observable part of the Universe. In other words we can ask: how much mass is contained within the volume that we can have observed since the Big Bang? The radius of the observable Universe is about 10,000 Megaparsec (or about 3 ~ 1026 metres). Using the above estimate for the total density this gives a total mass in the observable Universe of about 1054 kilogrammes. That's the best answer I can give for the mass of the Universe!"

According to the following passage,

RADIUS: ~ 300 Yotta meters or 3 x 10^26 m

DENSITY: ~10^-26kg/m3

TOTAL MASS: ~ 6 x 10^53 kilogrammes.Q: "Do you know where I can find an estimate of the total mass of the universe?"

Submitted by [email protected] 10/00

A: "If the Universe has "flat" or "open" geometry, then formally it has infinite volume, and therefore infinite mass. Something which is better defined is the mass within the "Observable Universe", which means the part of space from which we can have received light in the history of the Universe so far. This gets bigger every day!

The approximate answer is that the radius of the observable Universe is currently estimated to be about 300 Ym (that's "yotta-metres", or 10^24m, which is the largest SI prefix!). So you take that number, cube it, and multiply by 4/3, to get the volume of the whole sphere.

Then you have to decide what density you want to use. Are you only interested in luminous matter, or do you want to include all the baryons (regular stuff made of protons and neutrons)? Or do you want all the particle dark matter too? And what about the dark energy? If you include everything, then the average density in the Universe today is about 10-26kg/m3. And the mass in the observable Universe can be estimated accordingly.

There are several uncertainties and approximations here though - so don't expect your answer to be much better than an order of magnitude estimate!"