How much does the universe weigh?

[Leovinus]

Ok, so I'm mixing up mass and weight. But if you took the mass of the universe and put it on a scale in a 1-G gravity well, how much would it weigh?<br /><br />I ask this rather silly question because I've heard it said that if the universe has sufficient mass then it will collapse back into a big crunch but that if there is not enough mass it will expand forever and cool off into nothingness. I've also heard it said that they haven't been able to find enough mass in the universe to keep this second scenario from happening. Therefore, one might presume they know what the universe weighs based on detected mass.<br /><br />Ok, so how much does the universe weigh? <div class="Discussion_UserSignature"> </div>

 

[thechemist]

From this page :<br /><br />"The mass density of visible matter (i.e., galaxies) in the Universe is estimated at 3e-28 kg/m^3 (3e-31 times the mass density of water). The radius of the visible Universe is estimated at 1.7e26 m (18 thousand million lightyears) plus or minus 20 percent or so. <b>This yields a total mass of the visible matter of about 6e51 kg (1.3e52 lb)</b>, which is equivalent to the weight of 4e78 hydrogen atoms. Since nine out of ten atoms and ions in the Universe are in the form of hydrogen, this is a reasonable estimate for the number of atoms in the Universe (based on the visible galaxies only). Maybe a correction factor of the order of 2 has to be applied to account for the warping of space on very large scales.<br /><br /> However, there is considerable uncertainty about the mass density of all matter (visible and invisible) and energy (through Einstein's E = mc^2 equation). When one studies the movement of matter in and around galaxies, then it appears that up to about 10 times more mass is pulling at the matter (through its gravity) than is accounted for in the visible stars. This is the "missing-mass" problem. If this factor of ten holds throughout the Universe, then <b>the total mass in the Universe would be about 6e52 kg</b>. If the missing mass were mostly in the form of hydrogen atoms (which is not at all clear) then the number of atoms would be about 4e79.<br />" <div class="Discussion_UserSignature"> <em>I feel better than James Brown.</em> </div>

 

[yevaud]

Please note that the mass figure given by TheChemist can also be stated as "Brando's." The figure mentioned is the mass-equivalent of 6.937 Marlon Brando's - when he was developing his own gravity field. <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>

 

[najab]

How much does the Universe weigh? All.

 

[icemanmd]

You Couldn't put it on the scale, as there would be nothing for the scale to sit upon. This ruining your scaling test.<br /><br />I would venture to guess it would equal less then all the mass outside of the universe. (makes you think huh)