# How can we weigh insurmantable things , such as the Hydrogen Atom , the Observable Universe etc ?

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How can we know the weight of the Atom , observable Universe , etc ?

In: Physics

A minor point of clarification. We are measuring their *mass* not their *weight*. Objects of the same mass can have different weights depending on the gravitation field.

And we can measure the mass of different objects differently.

For things like atoms, what we can do is ionize them (by adding or removing electrons) which gives them an electric charge. We can then emit a stream of them across a charged field and see how much the path of the stream is bent by the field. How much it bends depends on the strength of the respective electric charges and the distance from the stream to whatever is emitting the field.

If we keep the distance constant and the magnitude of the generated field constant and known, then the only variable/unknown is the magnitude of the electric charge of the atoms. Since we know everything else and we know how they all relate to each other, we can therefore calculate that unknown value.

Since a positively charged hydrogen atom is just a single proton, knowing its charge gives us the mass of a single proton, from which we can then derive the masses of all the other atoms.

At the other end, with the universe, we know that the mass of objects warps space and can bend the trajectory of light (this is known as gravitational lensing). The more massive the object, the greater the bend. But rather than actually measure the mass of every object in the universe, we take some large portion of it and calculate its density (that is, the amount of mass in a given volume) and statistically estimate the total mass of the universe as far as we can see.

The weight of an atom is actually surprisingly easy to find. I’m not sure of the most common method, but an easy one that comes to mind is removing an electron from your atom, firing it at a known speed, and seeing how much it is deflected by a magnetic or electric field. In either case, its deflection gives you a value for its mass. By adjusting the strength of your magnet, you can get very precise measurements of your atom’s mass based on the charge of an electron.

The mass of the observable universe can only be estimated. However, we can estimate it with relative accuracy. I say relative because it is only accurate within an order of magnitude or more. The difference between a dollar and a hundred dollars. Seems big, but when talking about things so immeasurable that’s considered a good measurement.

You can look at how much mass is in a certain area based on its gravity pulling things nearby, and apply that to everything we can see. There are other approaches, but that’s a simple one.