How cold is space? The physics behind the warmth of the universe

Even though sci-fi movies would lead us to believe that space is incredibly cold—even freezing—that space itself isn’t exactly cold. In fact, it actually has no warmth at all.

Temperature is a measure of the speed at which particles move, and heat is how much energy an object’s particles have. So in a truly empty space region, there would be no particles and no radiation, so no temperature.

Of course, space is full of particles and radiation to generate heat and warmth. So how cold is space, are there any regions that are truly empty, and are there any places where the temperature drops to absolute zero?

How do stars heat space?

The hottest regions of space just around seniorscontaining all the conditions to initiate nuclear fusion.

Things get really hot when radiation from a star reaches a point in space that contains lots of particles. This gives the radiation from the stars. Sun something to really take action on.

For this reason Soil It is much hotter than the region between our planet and its star. The heat comes from particles in our atmosphere that vibrate with solar energy and then slam into each other, which disperses that energy.

Yet proximity to our star and having particles is no guarantee of warmth. Mercury — closest to the sun — extremely hot during the day and icy cold at night. Their temperature drops to 95 Kelvin (-288 ⁰Fahrenheit/-178 ⁰Celsius).

A Voyager 2 image of Uranus

False-color composite image of surface temperature changes on the surface of Uranus taken by Voyager 2. (Image credit: NASA)

Temperatures drop to -371 ⁰F (-224 ⁰C) Uranusmaking it even colder than on the planet farthest from the sun, NeptuneIt has an incredibly cold surface temperature of -353 ⁰F (-214 ⁰C).

This is the result of a collision with an Earth-sized object, causing Uranus to orbit the sun with an extreme inclination, causing it to be unable to hold on to its own internal heat.

Particles far from stars are so spread out that heat transfer through anything but radiation is impossible, meaning temperatures drop radically. This region is called the interstellar medium.

The coldest and densest clouds of molecular gas in the interstellar medium can have temperatures of 10 K (-505 ⁰F/-263 ⁰C or ), while less dense clouds can have temperatures as high as 100 K (-279 ⁰F/-173 ⁰C).

What is cosmic background radiation?

The Cosmic Microwave Background seen from the Planck satellite

An image of the cosmic microwave background radiation that fills the universe with a temperature of 2,725 K (-450° F/-270 ⁰C). (Image credit: European Space Agency)

this Universe so vast and filled with so many objects, some extremely hot, others unimaginably cold, it must be impossible to cast a single warmth into space.

Yet something permeates our entire universe with a temperature equal to 1 in 100,000. In fact, the difference is so insignificant that the variation between hot spot and cold spot is only 0.000018 K.

This is known as cosmic microwave background (CMB) and has a uniform temperature of 2.7 K (-45⁰F/-270⁰C). Since 0 K is absolute zero, this is a temperature just 2,725 degrees above absolute zero.

The CMB is a remnant from an event that occurred just 400,000 years later. Big Bang is called the final scattering. This was the point at which the universe later ceased to be opaque. electrons attached to protons forming hydrogen atoms, which prevent electrons from scattering infinitely and allow photons to circulate freely.

As such, this “frozen” fossil remnant in the universe represents the final point at which matter and photons align in terms of temperature.

The photons that make up the CMB were not always this cold, it took about 13.8 billion years to reach us, the expansion of the Universe redshifted these photons lower their energy levels.

The initial temperature of the radiation that created the CMB, which appeared when the universe was much denser and hotter than it is now, is estimated to be around 3,000 K (5,000° F/2,726⁰C).

As the universe continues to expand, this means that space is colder than ever and is getting colder.

What would happen if you were exposed to space?

If an astronaut is left to drift alone Space then exposure to the near-emptiness of space would not have frozen an astronaut, as is often portrayed in science fiction.

There are three ways of heat transfer, conduction by contact, convection when fluids transfer heat, and radiation by radiation.

Due to the lack of matter in empty space, conduction and convection cannot occur, and heat transfer occurs gradually only by radiative processes. This means that heat is not transferred quickly in space.

Because freezing requires heat transfer, an exposed astronaut—who only loses heat by radiative processes—dies from decompression due to a lack of atmosphere, much faster than freezing to death.