94: From Technological Warfare to Space Empire

Lecture Chapter 118

"This is Bose-Einstein condensate. The fifth state of matter."

"At this moment, all particles will exhibit the same state: there is no you, no me, no buildings, and no light or heat."

"All people and things that make up this world will be assimilated into the same state."

"In this state, thousands of atoms will behave like a superatom."

"They move in unison, act in unison, and exhibit many incredible properties, such as superfluidity, coherence, and nonlinearity —"

As Lin Yu spoke, he noticed that no one in the audience was whispering anymore; everyone was staring at him or at the formulas and diagrams on the blackboard.

In the corner, a boy wearing thick glasses raised his hand.

"Teacher Lin, I'd like to ask you something—" He paused, seemingly a little nervous.

"Just how cold is this BEC? Can our lab reach that temperature?"

Lin Yu nodded; this question had hit the nail on the head.

"Good question. The critical temperature of BEC depends on atomic density and mass."

"For typical experimental conditions, such as rubidium atomic gas with a density of 10 to the power of 12 to 10 to the power of 15 per cubic centimeter, the critical temperature is approximately between 100 nano-Kelvin and a few micro-Kelvin."

He wrote down a string of numbers: 1 microkilogram = 10 to the power of -6.

"That is to say, it is one millionth of a degree higher than absolute zero."

A collective gasp rippled through the audience.

Someone raised their hand; it was a middle-aged scholar in the second row: "Comrade Lin, I know this theory."

"Let's not talk about whether it's possible or not..."

"But the question is, does it really exist?"

This is a very pointed question, and it reflects the sentiments of many people.

Lin Yu didn't answer directly, but smiled and said, "That's a good question from the teacher."

Does BEC exist? My answer is yes, and it must exist.

He walked to the side of the podium, where a projector was placed, which Academician Wang had specially arranged to be moved from the Institute of Chemistry.

Lin Yu turned on the switch, and a complex chart appeared on the screen.

"This is the energy spectrum of the cosmic microwave background radiation."

Lin Yu pointed to the image: "It was measured by the COBE satellite and perfectly matches the blackbody radiation curve. Does anyone know the temperature of the background radiation?"

""

Someone in the audience answered, "2.725 Kelvin."

"That's right."

Lin Yu nodded. "But if we convert this temperature into energy and then substitute it into BEC's critical temperature formula, we get a very interesting result."

He wrote down line after line of derivations on the blackboard, each step clearly traceable.

When the final results came out, the elderly gentlemen in the front row sat up straight, while only Academician Wang, who had heard the results beforehand, remained calm.

What does this result mean?

Lin Yu turned around, his eyes shining: "This means that the universe itself must contain a giant Bose-Einstein condensate structure. Otherwise, this coincidence cannot be explained."

The venue was so quiet that you could hear the sound of water flowing through the heating pipes.

Lin Yu didn't stop; he continued speaking.

"How do we implement BEC in the lab? There are three core pieces of equipment needed."

He listed the following on the blackboard: "Laser cooling system, magneto-optical trap, ultra-high vacuum chamber."

He explained in detail the principles and parameters of each part. How does a laser reduce the speed of atoms to almost zero? How does a magnetic field trap cooled atoms? What vacuum level is needed to avoid collision interference?

None of these involve classified information.

As long as the key element isn't revealed, "thermal equilibrium is maintained by the laser collision rate. As long as the temperature is lowered below 170 nanokJ, condensation can be observed."

Someone couldn't help but ask, "170 nanokal? How much is that?"

Lin Yu smiled and said, "It's one seventeen millionth of a degree higher than absolute zero."

"It's like comparing our current room temperature of 16 degrees Celsius to the summit of the Himalayas, and absolute zero to the calm sea surface of the equatorial doldrums. 170 nanokal is the thickness of a sheet of paper placed on the sea surface."

A suppressed gasp rippled through the hall.

"but!"

Lin Yu emphasized his words.

"The bigger problem isn't temperature, it's density."

"The formation of BEC requires both low temperature and high density to be met simultaneously."

"Low temperatures make particles want to condense, and high density gives them the opportunity to collide."

"These two conditions are contradictory under normal circumstances: the lower the temperature, the more easily the gas becomes rarefied."

He paused, his gaze sweeping across the entire room.

"How to solve it? Evaporative cooling."

Lin Yu drew a simple diagram on the blackboard: a potential well with the escape path of high-energy particles marked on it.

"The principle is the same as drinking tea. Why does the hot water in the teacup cool down? Because the fastest water molecules break free and escape, taking energy with them."

"The average energy of the remaining molecules decreases, and as they reach equilibrium again, the temperature drops."

This analogy is so simple that even the students in the last row who were leaning against the windowsill understood it.

"In a magneto-optical trap, we can use a radio frequency field to precisely kick out the hottest atoms."

"By adjusting the frequency correctly, we can drive away only those atoms whose energy exceeds the threshold, without affecting the cold ones."

"By repeating this process, the temperature will continue to drop."

At this point, a student raised their hand: "Professor Lin, what's the use of doing BEC? Besides proving theories, what can it do?"

Lin Yu looked at the student, who was in his early twenties, about the same age as him.

"usefulness?"

Lin Yu smiled.

"The accuracy of atomic clocks can be improved by another order of magnitude. Current cesium atomic clocks are off by one second in three million years."

"With BEC, the difference might be as small as one second in 300 million or 300 million years. It can be used in satellite navigation, deep space exploration, and fundamental physics research."

He paused, then continued, "And then there's quantum computing. The atoms in BEC are in the same quantum state, making them a natural carrier of qubits."

"If we really want to build a practical quantum computer, we can't avoid the BEC path."

"And there's precision measurement, quantum simulation, and..."

Lin Yu spread his hands and shook his head helplessly: "There are many uses that we can't even imagine now. When Einstein wrote those equations seventy years ago, no one thought they could lead to the cosmic microwave background radiation."

The student paused for two seconds, then nodded vigorously and began frantically taking notes.

The lecture lasted for more than three hours, with only a ten-minute break in between.

Lin Yu explained everything from the definition of absolute zero to the implementation path of BEC, from the principle of laser cooling to the details of evaporative cooling, and from theoretical derivation to experimental design.

Every word he said was scribbled down in a notebook.

Finally, when it was getting light outside the window, Lin Yu stopped writing with chalk.

The blackboard was covered with writing, from Kelvin to Bose, from energy level diagrams to phase transition temperature formulas, densely packed like some kind of mysterious celestial script.

That's enough for today.

Lin Yu dusted off his hands with chalk dust: "If we keep talking, you guys will get hungry."

A burst of good-natured laughter rang out in the hall.

But no one moved.

Everyone was looking at him, as if they were waiting for something.

Lin Yu was stunned for a moment, then he understood.

He walked to the center of the stage and bowed to the audience.

Thank you everyone.

Then applause erupted, lasting for a full three minutes without stopping.