Are you gonna get meta about your physics question?

Interesting question. It seems the temperature of deep space is actually related to the heat transferred by the cosmic background radiation. Whatever is put in deep space doesn't get colder than that because of the radiation.

So temperature in a vacuum is related to electromagnetic rays passing through its space, heating whatever mass is in that space.

So I have this perfect vacuum right — Benj96

There's your first problem. You can't have a perfect vacuum. Even if you could build a container out of material that didn't give off any molecules into the center, and you could perfectly collect all of the molecules that were in the center and shuffle them out, there would still be stuff in the center of the container that you couldn't keep out... such as, for example, the photons that your heater shoots into there, and all the bajillions of neutrinos pouring through everywhere all the time.

More to the point, all of the energy fields the excitations of which constitute all the different kinds of particles exist constantly everywhere, just with different energy levels, different degrees of excitation.

Can I change the temperature of the vacuum? — Benj96

Yes. When your heater dumps radiation into there, it excites the electromagnetic fields inside of it, increasing the temperature in there. Of course those electromagnetic fields will dump that excited energy (the photons) out of it at literally the speed of light, transferring that heat to the surrounding container and beyond. Some of that might in turn scatter other photons back into the center of the container. Generally, by using your heater you're only briefly heating up the center of the container, but you're heating up the environment directly around the container which contributes to an ongoing increase of the temperature inside the container (as photons from the environment radiate back through the center over and over).

What temperature would my infrared camera measure in the center of the perfect vacuum? — Benj96

Your IR camera would see through the vacuum (because it's perfectly transparent to IR) and measure whatever is on the other side of it.

The average of "the other side of it" in every direction is effectively the temperature inside the center of the chamber. That's why the deepest of space, the most empty vacuum you'll find, is around 2.7 Kelvin: that's the average temperature coming from every direction, from the cosmic microwave background radiation.

How could my vacuum stay "cold" if it is enclosed in a jar with an outer ambient room temperature of 21c). If that were correct it would have a constant cooling effect on the room. Is it only the jar and outer world which would change temperature? — Benj96

Your vacuum chamber here is a perfect insulator of conductive and convective heat transfer, so even if we considered the inside of it absolutely cold, that wouldn't necessarily mean that it would constantly cool down the room around it, because no heat from the room could get conducted into it.

Consider for example why a piece of metal at room temperature in an average 21C room feels colder than a piece of wood at the same temperature. It's because the metal conducts heat away from your body much faster than the wood, so you feel the cold of the 21C (compared to your body's 37C) much more when touching the metal than the wood. Conversely, a piece of metal sitting out in the sun on a 40C day feels much hotter than a piece of wood that's been sitting out there. The vacuum is like the wood, but much more so: no matter how hot or cold it is in there, it's such a good insulator that nothing of your body heat (or the surrounding environment) is going to transfer into it or vice versa.

On the other hand, it's a perfect conductor of radiative heat transfer, which is just to say vacuum is transparent to all light. This means that the temperature of something on one side of it and something on the other side will equalize as quickly as radiative transfer will allow, and a thing on each side of the vacuum will observe the temperature of the vacuum to be exactly whatever temperature the thing on the other side of the vacuum is.

If I have one vacuum surrounded by an external environment of -100 degrees c and one that is + 100 degrees c is the center of my vacuums in both environments the same temperature despite the external conditions? I find this puzzling. — Benj96

One of them will be -100C and the other will be +100C, because they will both be surrounded on all sides by matter at those respective temperatures, so the amount of radiative heat constantly flying across them will be the amount corresponding to those respective temperatures.

Just like why deep space is 2.7K: that's how hot the CMB is.

There's also the Unruh effect. In theory if you were able to suspend your thermometer over a black hole with an anchor, due to the Unruh effect, it will experience a temperature by means of being in an accelerating frame.

So I have this perfect vacuum right (it cleans my house really well -jkjk). — Benj96

In other words, it really sucks. For vacuum cleaners, that's a compliment!

It seems that a substantial amount (>50%) of heat lost by human beings in a cool temperature is due to thermal radiation (mostly infared light?). I guess that is why mylar blankets work if you can insulate yourself well enough and why a thermos has a reflective material on the inside. It's counter-intuitive to think we're losing heat because were emitting so much light.

The temperature fluctuations due to EMR in space are glaring due to the lack of an ambient buffering system (atmosphere, et cetera).

this was explained so well.

To try and heat vacuum would be like trying to find the weight of a beauty. Presumably, in both cases, heat and weight, there's a necessity for some matter to be heated and pulled on by gravity.

Thanks!