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What do a sweaty summer afternoon, a pressure cooker, Mount Everest, and the vacuum of space all have in common?

At first glance, absolutely nothing.

Yet they are all governed by the exact same laws of physics.

A simple conversation about why humid weather feels uncomfortable eventually transformed into an incredible journey through thermodynamics, atmospheric pressure, high-altitude cooking, and even a real NASA accident involving the vacuum of space.

Let's follow that journey.

Part 1: Why Humid Days Feel So Much Hotter

Most people believe sweat cools the body.

That's only partially true.

Sweat itself doesn't cool you.

Evaporation does.

When sweat evaporates from your skin, it absorbs heat from your body. This process carries energy away, lowering your skin temperature.

On a dry day:

• Sweat evaporates quickly.

• Heat escapes efficiently.

• You feel cooler.

On a humid day:

• The air already contains a large amount of water vapor.

• Sweat struggles to evaporate.

• Heat becomes trapped against your body.

• You feel much hotter than the thermometer actually indicates.

In other words, humidity doesn't create extra heat.

It simply prevents your body from getting rid of the heat it already has.

Part 2: Is a Pressure Cooker Just Extreme Humidity?

This naturally raises an interesting question.

If humid air traps heat around our bodies...

Is the steam inside a pressure cooker simply "super humid air"?

Not exactly.

Although both involve water vapor, they behave in completely different ways.

Humid Weather

Humidity works by preventing cooling.

Your body tries to lose heat through evaporation, but the moist air slows that process down.

Result:

• Less cooling

• More discomfort

Pressure Cooker

A pressure cooker does the opposite.

Instead of trapping your body's heat, it actively forces additional heat into the food.

Here's why.

The Hidden Energy of Steam

When water boils, it transforms into steam.

But steam contains something special called latent heat.

This is hidden thermal energy stored during the phase change from liquid to gas.

Inside a sealed pressure cooker:

• Steam pressure increases.

• Water cannot boil at 100°C anymore.

• The boiling point rises to approximately 120°C.

When this 120°C steam touches cooler food:

• It instantly condenses back into liquid.

• During condensation, it releases all of its stored latent heat.

That enormous burst of energy cooks food dramatically faster than ordinary boiling water.

This is why pressure cookers can soften tough meat in minutes instead of hours.

Part 3: The Mountain Cooking Paradox

Now imagine taking your kitchen to the top of a mountain.

Many people assume lower pressure should make food cook faster.

Surprisingly...

The exact opposite happens.

The Rule of Atmospheric Pressure

At Low Pressure (High Mountains)

• Less air pushes down on water.

• Water boils sooner.

• Boiling point decreases.

• Water contains less heat.

• Food cooks more slowly.

At High Pressure (Pressure Cooker)

• More pressure pushes down on water.

• Water must become hotter before boiling.

• Boiling point increases.

• Water contains more heat.

• Food cooks much faster.

This explains why cooking on mountains often requires extra cooking time.

On Mount Everest, water boils at only about 68°C.

That means your potatoes are cooking in water that isn't even as hot as many cups of coffee.

Since food cooks because of temperature—not because bubbles appear—it takes much longer to finish cooking.

Part 4: The 40°C Boiling Water Thought Experiment

Understanding boiling points leads to a fascinating question.

Imagine water could boil at just 40°C.

Would it still burn you?

The surprising answer is...

No.

Boiling simply means a liquid is changing into a gas.

It does not automatically mean the liquid is dangerously hot.

Forty degrees Celsius is approximately the temperature of a comfortable hot tub.

If water boiled at 40°C, you could safely place your hand into it.

The bubbles might look dramatic.

But the temperature itself would be perfectly safe.

Could This Ever Happen Naturally?

Not on Earth's surface.

Even the summit of Mount Everest still has too much atmospheric pressure.

To make water boil at only 40°C, you would need an atmospheric pressure of roughly 7.4 kPa.

That pressure exists approximately 19 kilometers above Earth, inside the lower stratosphere.

Beyond that altitude, physics starts becoming very strange.

Part 5: The Armstrong Limit—Where Humans Begin to Boil

Around 19 kilometers (63,000 feet) lies a critical boundary known as the Armstrong Limit.

Above this altitude, atmospheric pressure becomes so low that water boils at normal human body temperature.

This raises a frightening question.

If humans entered such a low-pressure environment...

Would the water inside our bodies begin boiling?

The answer is yes.

Without a pressurized suit, exposed body fluids would begin to boil.

The 1966 NASA Vacuum Chamber Accident

This isn't just theory.

It actually happened.

In 1966, NASA aerospace engineer Jim LeBlanc was testing a spacesuit inside a large vacuum chamber.

During the test, a pressure hose accidentally disconnected.

His suit rapidly lost pressure.

Before losing consciousness, he later described one unforgettable sensation:

"I could feel the saliva on my tongue beginning to boil."

Fortunately, technicians quickly restored pressure to the chamber, and he survived without permanent injury.

His experience remains one of the most famous accidental human exposures to near-vacuum conditions.

Why Boiling Saliva Doesn't Burn

This sounds terrifying.

Yet something even stranger happens.

Boiling saliva doesn't burn your tongue.

It actually cools it.

Why?

Because evaporation requires energy.

As saliva rapidly changes into vapor, it absorbs heat from your tongue.

Instead of feeling fire...

Your tissues rapidly lose heat.

The Real Dangers of Vacuum

Boiling saliva isn't what kills someone in space.

The real dangers are far more severe.

1. Hypoxia

Without atmospheric pressure:

• Oxygen instantly leaves your lungs.

• Blood can no longer carry oxygen efficiently.

• Brain function rapidly shuts down.

Loss of consciousness occurs in roughly 10–15 seconds.

2. Ebullism

Your blood contains dissolved gases.

In extremely low pressure, those gases come out of solution and form bubbles inside body tissues.

This process is called ebullism.

Symptoms include:

• Severe body swelling

• Expansion of soft tissues

• Distorted appearance

• Serious circulatory problems

Fortunately, human skin is surprisingly strong and prevents the body from literally exploding.

One Law of Physics Connects Everything

The next time you boil water for pasta, remember what you're actually witnessing.

Those tiny bubbles obey the same physical principles that explain:

• Why humid summer days feel unbearable.

• Why pressure cookers cook food so quickly.

• Why meals take longer to cook on Mount Everest.

• Why astronauts need pressurized suits.

• Why humans cannot survive in the vacuum of space.

From your kitchen stove to the edge of space...

It's all the same physics.

Final Thoughts

Science often begins with ordinary questions.

Why is today so humid?

Why does a pressure cooker work?

Why does water boil?

Follow those questions far enough, and they lead beyond the kitchen, beyond the mountains, and ultimately into the unforgiving vacuum of space.

Sometimes the most fascinating scientific journeys begin with something as simple as watching a pot of water boil.