# Can you practically measure an infinite amount of some quantity?

• I
• MathematicalPhysicist
Now suppose the quantity that is being measured exceeds the capabalities of the measuring device either from above or below. How can we know if this quantity is indeed finite and not infinite?If the instrument is "pegged high" all you can say is, the process value exceeds the upper limit.

#### MathematicalPhysicist

Gold Member
Suppose we measure some speed or energy of something with a suitable device or instrument. Now suppose the quantity that is being measured exceeds the capabalities of the measuring device either from above or below. How can we know if this quantity is indeed finite and not infinite?

Your subject line and your question are completely different. Which is it that you want to know?

phinds said:
Your subject line and your question are completely different. Which is it that you want to know?
What is in the body of the text.

MathematicalPhysicist said:
Now suppose the quantity that is being measured exceeds the capabalities of the measuring device either from above or below. How can we know if this quantity is indeed finite and not infinite?
Generally if an instrument is "pegged high" all you can say is, the process value exceeds the upper limit. You can't say anything about "by how much" it is exceeded.

MathematicalPhysicist
phinds said:
Your subject line and your question are completely different. Which is it that you want to know?

I wonder how come I never thought of these questions before when I was much younger than now...

gmax137 said:
Generally if an instrument is "pegged high" all you can say is, the process value exceeds the upper limit. You can't say anything about "by how much" it is exceeded.
That's what I thought. So perhaps there are infinite quantities, but we can never know for sure.
Edit: At least experimentally we can't know for sure, but theoretically I guess we can 'know', or believe.

I think if something is created by a finite physical device, it cannot be infinite regardless of any ability to measure it. For example, I do not believe that any physical device that creates a voltage could create infinite voltage.

phinds said:
I think if something is created by a finite physical device, it cannot be infinite regardless of any ability to measure it. For example, I do not believe that any physical device that creates a voltage could create infinite voltage.
I agree. But take for example Geiger counter it doesn't create the radiation it measures.
Well I am not sure how this counter works, but I'll read.

MathematicalPhysicist said:
I agree. But take for example Geiger counter it doesn't create the radiation it measures.
Well I am not sure how this counter works, but I'll read.
If the universe is infinite, which it might be, then there will be an infinite amount of radiation, but not all within reach of a single detector.

To measure an infinite voltage would require a voltmeter with infinite insulation resistance, and an infinite digits display. But you might measure a voltage gradient per unit length, then extrapolate that across an infinite universe.

To measure an infinite current would require the current flow through a zero resistance ammeter, with an infinite digits display. But you might measure a current density per unit area, then extrapolate that across an infinite universe.

MathematicalPhysicist
If the universe is bounded, the number of particles of any sort must be also bounded, therefore numerable in theory. Thus no flow (all measurements are of flows/differences of some type) can be infinite because there are not infinite particles to sustain such a flow. The quantum nature of a bounded universe would not permit any physical infinities of a material nature.