Pratica di Shadowing: No device could prove Einstein wrong... until now - Impara a parlare inglese con i video
Scegli una modalità di pratica
Ogni modalità apre una sala di pratica a schermo intero.
467 frasi
Se le frasi sono troppo corte o troppo lunghe, clicca su Edit per modificarle.
1
This might be the most ambitious long -shot precision experiment that I've ever seen.
2
Scientists have put one atomic clock down in Boulder, Colorado, and one up in this observatory 4 ,000 meters above sea level,
3
and they're going to try and measure the difference in time dilation according to general relativity.
4
Because up here, time itself should be passing faster relative to down in Boulder.
5
If you go into a science center, often they will explain gravity as the bending of space -time,
6
and what they will have is a little funnel where the particle goes around the funnel,
7
and that's meant to give you an impression of why the Earth goes around the sun.
8
But that's not actually what happens.
9
It's not as much that space is curving, it's that time is stretching.
10
So the dominant effect of gravity
11
that we experience is the slowing down of time as we get closer to a massive object.
12
This is one of the predictions of Einstein's general theory of relativity, and it actually predicts how much faster the mountain clock should be ticking.
13
Put one clock in Boulder and another 2 .7 kilometers higher, and the mountain clock should gain about 25 billionths of a second every day.
14
This effect of general relativity and time dilation has been proven in experiments time and time again.
15
So why are we still testing it?
16
Because we know that at some quantum scale, this theory of gravity is going to stop working.
17
The way we know there is some contradiction is that
18
We know that particles can be in a superposition of two places, here and there.
19
That's what quantum mechanics tells us.
20
And what Einstein's theory of general relativity tells us is that if a particle is here, it bends spacetime in a certain way.
21
And if it's there, it bends spacetime in a certain way.
22
So what happens to spacetime if a particle with mass is in two places at once?
23
We don't have an answer to that question.
24
Einstein's theory of general relativity is silent on the question of what happens to space -time when a particle is in superposition.
25
And that leaves us with one of the biggest unanswered questions in physics.
26
Does gravity itself obey the rules of quantum mechanics?
27
So, teams around the world are trying to pin down exactly where gravity might stop following Einstein's prediction.
28
And they want to find out if there's a correction term needed in the equations
29
that might completely change your understanding of the universe.
30
Which means three massive challenges.
31
1. Build a clock so accurate it can track time to 18 decimal places.
32
2. Take that clock out of the lab and into the sky.
33
3. Find a way to read a signal so fast that electronics can't even process it.
34
This is the National Institute of Standards and Technology in Boulder, Colorado.
35
NIST has an atomic clock that is so accurate that if it started counting when the universe began,
36
it would not have lost or gained a second up until now.
37
NIST has been home to pretty much every kind of atomic clock ever made, from tiny chip scale clocks
38
and the most accurate clock on Earth to the first experimental atomic clock from way back in 1949.
39
And it's that accuracy that makes atomic clocks powerful tools for testing fundamental physics.
40
This little survey marker is actually in every room
41
that has an atomic clock at NIST and it's the official telling of
42
which altitude you're at above sea level so that you can take it into account for when you're aligning the atomic clocks.
43
They even connect to clocks that are 400 kilometers off the Earth's surface on the International Space Station through this little dome.
44
Now you might think that an atomic clock runs on radioactivity
45
because after all we use radioactive decay
46
and the half -life of elements to date things
47
that happened billions of years ago and we can do that with an error of less than 1%.
48
But that is not how an atomic clock works.
49
For keeping time, we need something that will oscillate back and forth.
50
For a grandfather clock, it's a pendulum.
51
And for a wristwatch, it's a piece of quartz that is vibrating under an electric current.
52
But an atomic clock gets its frequency from a fundamental property of the atom itself.
53
Electrons can only occupy specific energy levels and they can jump from one level to another by absorbing a photon of light.
54
But this only happens when a photon's energy matches the energy difference between the two levels, and the energy of a photon depends on its frequency.
55
So you can use a laser, tune its frequency, and that will change the energy of its photons.
56
Now, most frequencies are simply ignored, but when the frequency of such a laser is just right,
57
you get this transition and the electron makes the jump.
58
And that tells us the atom's natural resonant frequency.
59
Now we can tune the laser to match that frequency exactly.
60
And it's the oscillations of this laser light that act as the atomic clock's pendulum.
61
So this is NIST F3.
62
It's one of the cesium fountains we operate here at the National Institute of Standards and Technology.
63
We use these machines in order to experimentally realize the definition of the SI second.
64
What is the exact frequency?
65
Count to 9 ,192 ,631 ,770.
66
And after you've counted that high, you've counted exactly one second.
67
This clock feeds into a network that helps determine
68
Coordinated Universal Time, or UTC.
69
It's the standard that keeps your phone, your computer, and much of the world synchronized.
70
Now, since 1967, the time it takes for this exact number of cesium -133
71
oscillations to get past your detector has been the official definition of one second.
72
Keeping clocks synchronized with each other is a centuries -old problem, and that's because every oscillator has inconsistencies in the way that they're made.
73
But for atoms, it doesn't matter where you get the atom from.
74
The natural resonant frequency is the same for all atoms of the same element across the universe.
75
And it's the arrangement of these electrons, in particular isotopes, that make a very good atomic clock.
76
So these atoms give us ticks that are incredibly consistent.
77
How reliably one tick matches the next is the clock's stability.
78
Some elements are more stable than others, which is why cesium -133 is really popular.
79
But there's another challenge.
80
It's one thing for every tick to be consistent.
81
It's another to know that you're measuring the atom's true ticking rate.
82
In other words, how close is our measurement to the true atomic frequency?
83
That is accuracy.
84
And unlike the atom itself, accuracy comes down to how well the clock is built.
85
Now, the best cesium atomic clocks are over 50 billion times more accurate than the quartz crystal in your wristwatch.
86
The overall performance of a clock can be described by how many seconds it will gain or lose in a given time,
87
expressed as an order of magnitude.
88
So, what order of magnitude is the cesium clock that we're now using to standardize time?
89
Those realize fractionally about a part in 10 to the 16 of accuracy.
90
So, over the course of maybe tens of millions or 100 million years, it would only lose of order a second.
91
But this is still not good enough to find where gravity might stray from the predictions of general relativity.
92
If you want a more accurate clock, you can start with finding a higher resonant frequency.
93
Because the more oscillations you can pack into a second, the more finely you can define it.
94
And it turns out that elements have different natural frequencies, so you just have to find one that fits.
95
And the perfect candidate for the job is Iterbium.
96
I like to say it looks a little bit like iron pyrite, like fool's gold.
97
While cesium clocks operate in the microwave part of the spectrum, a terbium resonates in the optical band with a frequency 56 ,000 times higher.
98
This equates to 518 trillion oscillations every second,
99
and that allows for accuracies of 1 part in 10 to the power of 18.
100
So this clock won't gain or lose a second in more than the age of the universe.
101
But when the ytterbium is solid, the atoms are so close together that neighboring atoms pull each other's electrons out of place.
102
And this broadens and blurs the frequency at which the electrons make the transition.
103
And that makes the natural resonant frequency pretty much impossible to find.
104
So ytterbium first has to be turned into a gas.
105
There's an oven where we heat this up to about 500 Celsius.
106
We make a vapor of it
107
and then at the end of the oven there's actually a hole where just a stream of this stuff comes shooting out.
108
But now these atoms are traveling at around 300 meters per second, which causes a different problem.
109
If an atom is moving towards or away from a photon as it's hit, it will absorb the light at a different frequency.
110
This is called a Doppler shift, and it alters the reading of the natural resonant frequency by one part in a million.
111
An error at the sixth digit, when you're aiming for 18 digits of accuracy, would end the experiment there.
112
So the team has to find a way to slow down the atom's movement once they've reached the main vacuum chamber.
113
You have to cool them down in three dimensions in free space, and so that requires having these laser beams in three dimension as well.
114
So the blue laser operates first.
115
It takes the hot beam of atoms that are at hundreds of Kelvin temperature
116
and brings them all the way down to about a millikelvin or a thousandth of a degree above absolute zero.
117
And then it trades off with the green laser, also propagating along the same axes.
118
And that takes those millikelvin temperature atoms and brings them down to about a microkelvin or so.
119
It might seem counterintuitive that you can cool atoms by firing lasers at them,
120
but what the scientists are doing is using different electron transitions inside Ytterbium -171.
121
They're now taking advantage of that Doppler shift.
122
The lasers are tuned just below the frequency the atoms absorb, so an atom only absorbs light from a beam it's moving towards.
123
And because light carries momentum, each photon it absorbs gives it a tiny kick slowing it down.
124
The atom then emits a photon in a random direction,
125
so over many cycles those random emissions average out while the absorbed photons keep slowing the atoms down.
126
Overall, the lasers can cool the atoms down to just a millionth of a degree above absolute zero.
127
Now, once the atoms are cold, the next challenge is keeping them in one place, and it turns out you need a laser for this too.
128
We'll focus a beam into our vacuum system where the yaterbium atoms are located,
129
and then we'll actually just put a mirror there to reflect it back onto itself.
130
And if we could kind of zoom in enough,
131
we'd see that there's this interference pattern between the two directions that leads to nodes and antinodes of laser intensity.
132
The outgoing and reflected light waves overlap, and in some places they cancel each other out, and in others they reinforce each other.
133
And the result is a repeating pattern called a standing wave.
134
Now, the Iterbium -171 atom is neutral.
135
The charges of its protons and electrons balance out but light is an electromagnetic wave.
136
So the laser beam carries an electric field, and that electric field pulls those charges very slightly in opposite directions.
137
This is called an induced dipole, and it gives the atom a potential energy so that now the electromagnetic force can act on it.
138
The strength of the field varies along that same pattern as the standing wave.
139
The electric field is weakest at the nodes of the wave and strongest at the antinodes.
140
This gives the dipole a potential energy,
141
causing the atom to be drawn closer and closer to the antinode until the field strength starts to level out.
142
You can think of this like holding a marble on the lip of a bowl.
143
Here, the marble has maximum gravitational potential energy, and when you let the marble go and it moves down the slope,
144
the potential gets smaller and smaller until at the bottom of the bowl, it reaches a minimum.
145
The marble can't climb back out of the bowl, so it's trapped.
146
Now, in the same way, the atom is drawn by the electric force away from the
147
point of maximum potential energy to where the potential reaches a minimum.
148
This formation is called an optical lattice.
149
Now the atoms are trapped in antinodes just 300 nanometers across
150
and their movement is so limited that it no longer impacts the measurement.
151
And at last the clock's frequency can be read out.
152
So this software we're looking at the actual clock operation.
153
So over here we measure the number of atoms in the ground state
154
and then here we measure the number of atoms in the excited state.
155
That balance is how the NIST scientists know the laser is still locked onto the atom's natural frequency.
156
So the laser becomes a stand -in for the atoms.
157
Count its oscillations, about 518 trillion of them, and that's a second.
158
You can see that there's this large central chamber which has all of the windows on it.
159
That's where the lasers are inserted into the system.
160
I mean, one question that is in my mind as you're explaining this is, if this is the setup here and you know the lasers
161
that you're using to treat it are on that bench and in the room across the hall.
162
How do you bring this up a mountain?
163
To measure the effect of gravity on time the clock needs to run at different elevations
164
and that means climbing to 4 ,326 meters above sea level to the top of Mount Blue Sky.
165
Oh is that the observatory right there?
166
That is right up there yeah that's where we're headed.
167
Well this is a This is a proper trail.
168
Kind of on the final bends now.
169
We're nearly there.
170
So we just got to the observatory.
171
I went on this little walk to video the view.
172
And I'm kind of out of breath going downhill from up there.
173
That looks pretty cold, Gregor.
174
But this job gets you into some wild situations, whether you're at 14 ,000 feet or stranded out here in the desert.
175
The question is, how do you protect yourself in such extreme environments.
176
Got 60 seconds on the clock.
177
Let's go.
178
Scorching in the desert heat?
179
Wear plenty of sunscreen, drink a lot of water, and find whatever shade you can.
180
Risking it all to settle a physics debate?
181
It feels makeshift, I'm not going to lie.
182
Time to wear a crash helmet and trust in the engineering.
183
Investigating a public health crisis?
184
If it weren't so dangerous, it'd be a fun activity to do.
185
Well, it might be time for a full hazmat and a respirator.
186
What about online scams?
187
Well, that's easy.
188
Use NorVPN's anti -bars.
189
It's like a hazmat suit for the internet.
190
NordVPN is preventive, and it works to block scams and phishing attempts before they happen.
191
The anti -malware functions proactively.
192
It scans downloading files and removes them if they're dangerous.
193
And while most VPNs don't protect you against fake web stores, NordVPN's next -gen antivirus does.
194
It's all built right into the NordVPN app, giving you all -in -one digital security in just one tap.
195
So go big on your online protection with NordVPN's next -gen antivirus.
196
Just head to nordvpn .com slash veritasium or click the link in the description for an exclusive deal and four months extra.
197
It's completely risk -free with their 30 -day money -back guarantee.
198
I want to thank NordVPN for sponsoring this video, and now back to you, Gregor.
199
This is the biggest vertical separation ever attempted using high -precision clocks.
200
An experiment at altitude means contending with lightning storms, hail, and snow, even the local wildlife.
201
And this short summer weather window means they only have a few weeks to do it.
202
So we'll go into the tent here so we've got a couple of heaters
203
that keep the temperature a little bit more stable and it also keeps out this kind of invasive moth.
204
They get into the observatory there can be tons of them.
205
Anyways the tent does a nice job of keeping them off of the the lasers as well.
206
And is this this is everything?
207
This is really the same as what we were looking at before just on a little bit smaller scale.
208
So we've got down on this end is that
209
that hot oven where we have the atterbium atoms
210
that form the beam that travels down to the main chamber
211
and then some of the lasers that introduce the different colors for atomic manipulation.
212
But at the lab you had a pretty extensive optical bench building up all these lasers.
213
Is that all here?
214
Yep, that's all here.
215
Some of it is tucked away below and on this adjacent rack.
216
It's all here.
217
That's incredible.
218
The mountain clock has to be compared against the one running down in the lab.
219
The problem is, how do you get the clocks to communicate with each other?
220
Well, you could run a fiber optic cable all the way down to Boulder,
221
but it turns out the animals in the region would probably chew through it, and the infrastructure just isn't there.
222
So instead, the clock signal is beamed to a rooftop just outside of Denver.
223
But first, it has to travel from the clock in the tent through optical fiber to this box.
224
Comes out of the fiber, it gets into a small beam, and then it gets into a beam expander,
225
gets to a big beam it's about 10 centimeters going out the door.
226
But beams diverge and turbulence makes it wider.
227
So it's about a meter by the time it gets to Denver.
228
What is actually the line of side distance?
229
It is about 80 kilometers.
230
So you're aiming at one meter spotlight, 80 kilometers.
231
So it's an 8 micron core.
232
It's a very small target.
233
Um, so...
234
Wait, the light that you're trying to aim down is going into an 8 micron opening fiber optic cable?
235
Yeah.
236
That's insane.
237
The final part of the journey is made through optical fiber,
238
And the same path is taken in reverse by the signal from the lab clock arriving to the terminal on the mountain.
239
So the two clocks can be compared directly.
240
So we get all the signals going and then we come over to our computer.
241
Right now, we're seeing no light over the link.
242
We're measuring essentially the detector noise.
243
Our detection threshold is this dashed line here.
244
And so what we really want when we lock this up is we want to see this guy hanging out up here.
245
If we hit this find receive button.
246
And then you just see this pop up.
247
Yeah.
248
So that is light over the link.
249
So we've locked in.
250
We've locked in.
251
We found it.
252
With this link up and running, the experiment is finally underway.
253
But there is actually another team who is already looking beyond the mountains.
254
Because to test gravity to even finer scales, eventually a clock like this needs to get into space.
255
Which creates a whole new problem.
256
Because now, instead of hitting a stationary target, you have to hit one that is moving.
257
At the University of Western Australia, one team is trying to solve exactly that.
258
They've designed a system
259
they hope will send optical clock signals from a moving satellite down to the ground in just a few years' time.
260
And after trialling the link on pickup trucks and boats, now they're trying putting it on a helicopter.
261
So why start with a helicopter?
262
Certainly no one's put a clock on a helicopter before.
263
And for these sort of, I think scenarios where we're going to space, people want to see those stepping stones.
264
It's like a clock in a place that no one's ever put an optical clock before.
265
Atomic clocks have been on board satellites for decades, but they're microwave clocks, lower in both frequency and accuracy.
266
And their signals are beamed down using microwaves too.
267
Microwaves have a longer wavelength than visible light, so where a cloudy sky might absorb or scatter an optical signal,
268
microwaves can often still make it through.
269
So it might sound like the way forward is just to use microwave to transfer any signal,
270
but that longer wavelength is actually why it doesn't work for optical clocks.
271
See, to compare two clocks over a link you need to know exactly when the signal arrives,
272
and you work that out by measuring where each wave is in its cycle as it comes in.
273
Fluctuations in the atmosphere distort the signal.
274
Plus, there are all other kinds of noise, even from the equipment that detects it.
275
How strong the signal is compared with that noise is called the signal -to -noise ratio.
276
The more noise there is, the harder it is to work out exactly where each wave is in its cycle.
277
You can only pin it down to within a small fraction of a wave.
278
For a microwave, with its much longer waves, that small fraction of a wave lasts tens of thousands of times longer.
279
So your measurement could be out by tens of thousands of times more.
280
So to keep up with the precision of optical clocks, the signal has to stay at an optical frequency.
281
And that means hitting a moving target with a laser beam.
282
So this is the clock here and then we've got on top, this is our frequency transfer system and our beacon laser source.
283
That beacon laser will run alongside the clock signal as a bigger target for the ground station to track.
284
Everything that we have on the helicopter is completely reciprocal to what we have on the ground.
285
So they also have their own beacon laser that we look for when we're scanning around with our terminal as well.
286
But remember those fluctuations in the atmosphere?
287
Well those have to be accounted for too.
288
If you have lots of pockets of hot air rising from the road or over the city as well,
289
that will take our laser beam that we're trying to send and move it around and introduce a lot of errors.
290
So what we do is we have a very special mirror, we call it a tip -tilt mirror,
291
and what it does is it moves fast enough that it can account for all of those deviation angles that we're seeing.
292
How fast does it move?
293
So it's moving at about 600 hertz, so 600 times a second is the rate that it can move.
294
But yeah, so switching on the clock.
295
When the technical checks are done, the experiment is ready for takeoff.
296
Cocks up and running, let's go!
297
So we've just left Lilani, she's going to get into helicopter now and they're going to take off really soon so we're rushing back to UWA.
298
If it works the two beacons will lock onto each other
299
and the signal from the clock on the helicopter can be sent down and compared with a clock on the ground.
300
So this is the the roof of the physics building here at the University of Western Australia
301
and then Sabrina over here is looking at our local optical terminal so that's just in here.
302
You've been able to recognise a very similar one that was on the helicopter before.
303
Oh yeah look that's it there we can see it already.
304
Watch your heads.
305
Slightly terrifying.
306
Should be about it can you see anything yet?
307
So you've got to go up a fair bit.
308
Can we go more to the right?
309
Okay that should be about it.
310
Yeah got it.
311
You can see that little flash of light that's in through the door here.
312
That'll be the the beacon laser coming in here.
313
Oh okay so that's amazing.
314
But yeah I guess it's not yet well aligned enough to get the the link fully locked.
315
I think the problem is with that it's a bit windy today
316
and trying to have it like hovering it's actually like the least smoothest kind of flight configuration of the helicopter
317
so maybe we kind of get lucky
318
and we get like a little a flash occasionally
319
and we might get a little bit of data but that's not really the ultimate configuration we want to get.
320
How's it looking?
321
I mean we're seeing some sort of stuff moving around.
322
The issue is when we find ourselves spatially we still need to find ourselves spectrally.
323
The lasers can be gigahertz or tens of gigahertz off pretty easily.
324
How come?
325
At optical there's so much extra bandwidth that's available
326
but we still need to be within I don't know five megahertz of each other.
327
So pointing the beams at each other isn't enough.
328
The two lasers also have to be at almost exactly the same frequency.
329
To put that in perspective, a car radio only has to tune to within a fraction of a percent of a station to pick it up.
330
But these lasers have to match within a few parts in a hundred million.
331
So the terminal scans back and forth, hunting for a window thousands of times narrower than the range it's searching.
332
Okay, we've got 20 more minutes of fuel left.
333
Does that include going home time?
334
I don't know.
335
And they proved the system on the ground could find its partner in the sky, even if they only got a few brief locks.
336
It's not enough data yet to properly compare the two clocks, but it's a big step towards future ground satellite transfers.
337
In the end it sounds easy,
338
but all we have to do is make the mounts just track a bit better and just a bit faster and stuff.
339
And that's one thing that we can easily do, you know, with a bit more time and a bit more engineering.
340
Since then they've been up
341
Mount Fuji, testing their transfer system through two back -to -back typhoons.
342
I think our target is just down here.
343
Here's our terminal set up for the day.
344
Beautiful views all around.
345
Absolutely amazing.
346
Their link will help Hidetoshi Kotori's group at Riken
347
and the University of Tokyo do their own test of general relativity in the spring.
348
But there's one final problem, and that's because even if the link is established successfully,
349
there are still 518 trillion oscillations coming through those electronics every second.
350
And it turns out that there is no electronic device in the world that can read out signals this fast.
351
Even some of the fastest transistors can only switch on and off about 10 billion times a second.
352
And that's still 50 ,000 times too slow.
353
So for decades, scientists had a strange problem because they could build an optical atomic clock, they just had no way to accurately measure its signal.
354
What you'd need is some sort of reference to tie it to, at a frequency that you already know exactly.
355
For example, you could start with a signal in the microwave spectrum that was easy and familiar to create,
356
and then multiply its frequency up in stages until it reached the optical range.
357
And then you could find the exact frequency of the light
358
that you want to measure from the optical atomic clock by comparing it against the signal that you generated.
359
Okay, so I have two tuning forks here
360
and they're both at 440 hertz and when I hit them you can hear that they're both at the same frequency.
361
Now I've put a small weight on one of the forks and that is going to change the frequency slightly, so listen to what happens now.
362
You hear that sound?
363
So what you're hearing is a new waveform that is pulsing at the frequency difference between these two forks.
364
It's called a beat note.
365
And the same thing can be done with light.
366
You overlap two lasers of different frequencies and you get a beat note too.
367
And the thing is, Since the frequency difference is so much smaller than the signal that we're trying to find,
368
we can actually read it out using transistors and we can do a simple calculation.
369
The reference frequency that you know plus the beat note would equal the exact frequency of the unknown signal.
370
But there's a problem.
371
The visible spectrum alone spans around 400 ,000 GHz.
372
It's extremely broad and a beat note can only be measured
373
if the two signals are within a few tens of gigahertz of each other.
374
So the chances of your reference signal being close enough to the unknown signal that you're trying to find are really small.
375
What scientists needed wasn't one frequency, but many spread out so that the unknown signal would always sit close to at least one of them.
376
So a reference signal is down here in the microwave part of the spectrum.
377
So let's call that F of R and then our unknown signal is somewhere up here in the optical.
378
So F of optical.
379
So what I need is some sort of ruler
380
that is going to be able to quantify this difference in frequency between my reference signal
381
and my unknown signal of the clock that I'm trying to find.
382
In theory, you could set up a number of lasers to act as the notches of the ruler,
383
but this frequency in microwave and this frequency in optical are very far apart.
384
So if I want to bridge this gap, I would need a lot of lasers.
385
So instead, what would be useful is
386
if I could manipulate the light of just a single laser to produce all of these different frequencies at the same time,
387
something that would span all the way from the microwaves that electronics could count up to the light scientists wanted to measure. In 1994,
388
a German physicist called Theodor Hensch was at a trade show
389
when a demonstration of a new type of laser struck him with an idea.
390
See, for decades, he'd been coming up with different ways to try and measure optical signals.
391
But this particular titanium sapphire laser could generate incredibly short pulses of light, each packed with a vast range of frequencies.
392
Now, on a frequency graph, that light looked like the teeth of a comb.
393
This could finally be the ruler that everyone was searching for.
394
But to make the wide range of frequencies an effective ruler, each frequency needs to be related to the other frequencies,
395
otherwise you can't really predict the pattern.
396
I mean, a ruler is only useful if these notches are equally spaced.
397
So Hensch and his colleagues put the laser to the test.
398
They measured its light and found that the frequencies contained inside were perfectly evenly spaced.
399
This is an optical frequency cone. By 1999, a team in Boulder led by John Hall had engineered this comb into a ruler
400
so wide that it could measure almost any color of light.
401
So now I have a comb with, well, hundreds of thousands of teeth,
402
and some of them are going to be close enough to that unknown signal that I'm trying to find.
403
The comb is emitting its own frequency, so there's going to be a beat note that rings between this.. comb tooth and the unknown signal.
404
So by observing that beat note with a photodiode, we have a formula to calculate the frequency of our unknown optical signal.
405
That's the tooth position number multiplied by the repetition rate plus the frequency of the beat note.
406
And because the repetition rate is locked to our reference signal, every number in that formula is one that electronics can measure.
407
Within a year, frequency combs were reading the first optical atomic clocks.
408
Henschen Hall, alongside Roy Glauber, were awarded the 2005
409
Nobel Prize for this work.
410
On the mountain, each clock signal is being sent over the air using pulses of a frequency cone.
411
General relativity predicts that when you bring those pulses together,
412
the clock in the lab should take ever so slightly slower compared to the clock on the mountain.
413
That is the theory.
414
But what does the counter on the mountain actually say?
415
So that is light over the link.
416
So we've locked in.
417
We're locked in.
418
We found it.
419
So the fact that this is moving, slowly ramping, that's the time output changing because the clocks are running at different rates.
420
So the time offset is slowly ramping and we can see it more or less in real time.
421
Here it goes. If Einstein is right,
422
these two clocks should differ by 2 .885 times 10 to the power of negative 13 seconds every second.
423
This number has been calculated by another group based on measurements of the gravitational field in the lab and on the mountain.
424
And while both teams are working to many more decimal places than this,
425
they're actually keeping those final digits secret from each other until they're ready to compare findings.
426
If the clocks measure a different angle on the slope, well, that's evidence that general relativity might stop working at this level.
427
So a few weeks later, we hopped on a call with the team to check out what the data is saying. Is Einstein still right?
428
I'm going to answer that two ways.
429
The first is a very simple answer, which is yes.
430
Okay.
431
We have no evidence that says no. The second answer is that we're still analyzing the data.
432
So you're down at sort of the 13th digit
433
and a little change at sort of the a millionth of that slope
434
is what you're looking for when you're looking for new physics.
435
So it's a very small change.
436
I mean, it's incredible
437
that you have the sensitivity to look at a millionth of of this slope that is already a trillionth of a second. So, wow.
438
I mean, that's crazy.
439
And are you guys excited?
440
Are you nervous to know that the data is there?
441
You just have to crunch the numbers.
442
Are you sleeping well?
443
You got to kind of whatever it is, put that number out there and whether it agrees with the classical prediction or not,
444
that's a little bit of a nerve -wracking moment.
445
Yeah, I mean it's huge.
446
The best terrestrial test that's been done here on Earth is about at the 100 part per million level.
447
Our hope is
448
that we'll be able to do approaching the 10 part per million level with testing general relativity in a new
449
and deeper way.
450
Have you got any more of these tests planned in?
451
I think the big next step would be to try to for Link to Spice.
452
It'll be a few months before
453
Laura and Andrew's team are ready to share their final results.
454
So we've linked their groups page in the description if you want to follow their progress.
455
I wanted to say a huge thank you to them and the rest of the NIST team and to Sasha,
456
Lilani, and the team in Perth for all their help on this video.
457
And one final thing, you might have noticed that we launched a second channel called InGenius.
458
$72 billion.
459
That's how much money changed hands on prediction markets in September 2026 alone.
460
Their recent episode was about prediction markets and who actually wins on them.
461
Shockingly, it turns out it's just the 0 .1 % at the top.
462
The team scoured three years worth of past trades on Polymarket to find out what really happens on the platform.
463
And it's a really fascinating watch.
464
So if you're interested, I really recommend you check it out.
465
I want to thank you for your support.
466
And of course, as ever, thank you for watching.
467
Thank you.
Scarica l'app
Tutto ciò che serve per parlare fluentemente
Pronuncia con IAVoto per ogni frase
Pratica IPAPadroneggia ogni suono
VocabolarioCostruisci il tuo lessico
Gioco di vocabolarioImpara giocando
Stesso Canale
C11
White holes and wormholes are probably real. Here's why.
Daily ConversationUniversity Students
C11
Something is jamming GPS over Europe. Here's what we found
Daily ConversationUniversity StudentsWorking Adults
C11
Why It Was Almost Impossible to Make the Blue LED
Daily ConversationUniversity StudentsWorking Adults
C12
You've (Likely) Been Playing The Game Of Life Wrong
Daily ConversationUniversity StudentsWorking Adults
B22
We're trying something new...
Daily ConversationWorking Adults
C120
How does light 'know' the shortest path?
IELTS PrepTOEFL PrepUniversity Students
C13
Why Cold Drinks Were Deadly Before 1914
Business EnglishUniversity StudentsWorking Adults
C14
Exposing The Flaw In Our Phone System
Business EnglishUniversity StudentsWorking Adults
C12
Our Greatest Delusion
IELTS PrepTOEFL PrepUniversity Students
C13
The Most Controversial Problem in Philosophy
IELTS PrepTOEFL PrepUniversity Students
C13
We've Been Using The Wrong Science In Court For 50 years
IELTS PrepTOEFL PrepUniversity Students
B24
Explaining Pi With Pizza
University Students
B214
5 Fun Physics Phenomena
Daily ConversationUniversity Students
C12
The Absurd Engineering Behind the Internet
Daily ConversationUniversity StudentsWorking Adults
C11
The Most Misunderstood Concept in Physics
IELTS PrepTOEFL PrepUniversity Students
B11
Falling ladders - why does this happen?
IELTS PrepTOEFL PrepHigh School Students
C110
How a slinky falls in slow motion #shorts
University StudentsWorking Adults
C13
We're 99.9% sure this pattern is true, but no one can prove it
IELTS PrepTOEFL PrepUniversity Students
B23
What is the secret of a good life? Lessons from the longest study on happiness
Business EnglishDaily ConversationUniversity Students
C18
How An Infinite Hotel Ran Out Of Room
University Students
FOR YOU
Video consigliato
C11
508 frasi
Einstein and the Theory of Relativity | HD |
Daily ConversationUniversity Students
C13
147 frasi
We Traveled Back in Time. Now Physicists Are Angry.
Daily ConversationUniversity StudentsWorking Adults
C12
182 frasi
We Let $200 GPT-Pro Think for 7 Days on Unsolved Math
Daily ConversationUniversity StudentsWorking Adults
C13
59 frasi
How Can You Change Somebody's Opinion?
Daily ConversationUniversity StudentsWorking Adults
C12
58 frasi
Where is the evidence for God? | Bishop Robert Barron
Daily ConversationUniversity StudentsWorking Adults
C11
133 frasi
Has quantum mechanics proved that reality does not exist?
Daily ConversationUniversity StudentsWorking Adults
C11
215 frasi
This New Pyramid Theory Explains the Missing Evidence
Daily ConversationUniversity StudentsWorking Adults
C15
41 frasi
How Einstein changed time forever | Jim Al-Khalili for Big Think
Daily ConversationUniversity StudentsWorking Adults
C12
530 frasi
Human Immortality 4K | Can Science Defeat Aging?
Daily ConversationUniversity StudentsWorking Adults
C13
119 frasi
Mathematics and Physics | Lesson 2 | Understanding the Connection
Daily ConversationUniversity Students
Vocabolario e note di pronuncia per questa lezione
Questa lezione di conversazione si basa sul video “No device could prove Einstein wrong... until now”. Le parole che ritornano più spesso: clock, frequency, laser, signal, atom. Questo video contiene 344 frasi e 6029 parole da ripetere con lo shadowing. Il parlato dura 34:23. Chi parla ha un ritmo naturale di circa 175 parole al minuto, vicino a una conversazione quotidiana. Solo il 80% delle parole rientra nelle 3.000 più comuni dell’inglese, quindi il lessico è impegnativo.
Vocaboli chiave di questo video
15 parole del video che vale la pena imparare, con pronuncia e significato:
| Parola | Pronuncia | Significato |
|---|---|---|
| clock sostantivo | /klɑk/ | contachilometri, tachimetro |
| frequency sostantivo | /ˈfɹiːkwənsi/ | frequenza |
| laser sostantivo | /ˈleɪzɚ/ | laser |
| atom sostantivo | /ˈætəm/ | atomo |
| atomic aggettivo | /əˈtɑː.mɪk/ | atomico |
| beam sostantivo | /ˈbiːm/ | trave, asse |
| microwave sostantivo | /ˈmaɪkɹoʊˌweɪv/ | microonda |
| gravity sostantivo | /ˈɡɹævɪti/ | gravità |
| helicopter sostantivo | /ˈheliːˌkɔptə(ɹ)/ | elicottero |
| accuracy sostantivo | /ˈæk.jɚ.ə.si/ | esattezza, precisione |
| ruler sostantivo | /ˈɹulɚ/ | righello |
| comb sostantivo | /koʊm/ | pettine |
| physics sostantivo | /ˈfɪz.ɪks/ | fisica |
| experiment sostantivo | /ɪkˈspɛɹ.ə.mənt/ | esperimento |
| terminal sostantivo | /ˈtɚmɪnəl/ | terminal, terminale |
I phrasal verb che sentirai
| Parola | Significato |
|---|---|
| turn out verbo | risultare |
| find out verbo | scoprire |
| build up verbo | accumulare |
| check out verbo | investigare |
| come up with verbo | ideare, escogitare |
| go out verbo | uscire, andare fuori |
| go up verbo | salire |
| keep up with verbo | tenere dietro a |
Frasi da ripetere
Frasi brevi e complete del video che puoi riutilizzare nella conversazione di tutti i giorni:
- That's what quantum mechanics tells us.
- The question is, how do you protect yourself in such extreme environments?
- We're measuring essentially the detector noise.
- Can you see anything yet?
- We're seeing some sort of stuff moving around.
La grammatica di questo video
Le strutture che chi parla usa di più, con le parole esatte del video:
| Struttura | Nel video |
|---|---|
| Frasi condizionali if + frase, will/would + verbo — una condizione e il suo risultato | If it weren't so dangerous, it'd be · If it works the two beacons will lock |
| Present perfect have/has + participio passato — un’azione passata che conta ancora adesso | I've ever seen · have put · has been proven |
| Forma passiva be + participio passato — conta ciò che accade, non chi lo fa | has been proven · are simply ignored · is built |
| Frasi relative who / which + frase — un’informazione in più su una persona o una cosa | others, which is · chamber which has · answer, which is |
Pronuncia a cui fare attenzione
Chi parla usa 82 contrazioni e forme ridotte, come you're, we're, they're. Pronunciale nella forma breve, così come le senti.
- I suoni “th”: tooth /tuθ/, sixth /sɪksθ/, millionth /ˈmɪljənθ/, wavelength /ˈweɪvˌlɛŋ(k)θ/
- I suoni “sh” e “zh”: prediction /pɹɪˈdɪkʃən/, measurement /ˈmɛʒ.ə.mənt/, precision /pɹɪˈsɪʒ.ən/, fraction /ˈfɹæk.ʃən/, transition /tɹænˈzɪʃ.ən/
- Parole lunghe — attenzione all’accento: helicopter /ˈheliːˌkɔptə(ɹ)/, accuracy /ˈæk.jɚ.ə.si/, experiment /ɪkˈspɛɹ.ə.mənt/, electronics /ɪˌlɛkˈtɹɑ.nɪks/, observatory /əbˈzɜːvət(ə)ɹi/
I suoni difficili per chi parla italiano:
- /h/ — va soffiata, non è muta: helicopter /ˈheliːˌkɔptə(ɹ)/, hazmat /ˈhæzˌmæt/, hertz /hɝts/
- Consonante finale — senza aggiungere una vocale dopo: clock /klɑk/, atomic /əˈtɑː.mɪk/, microwave /ˈmaɪkɹoʊˌweɪv/, node /noʊd/, physics /ˈfɪz.ɪks/
- /æ/ — più aperta della “e”: atom /ˈætəm/, gravity /ˈɡɹævɪti/, accuracy /ˈæk.jɚ.ə.si/, absorb /æbˈsɔɹb/, fraction /ˈfɹæk.ʃən/
Come esercitarsi con questo video
- Ascolta tutto il video una volta senza parlare e annota le parole che non conosci.
- Inizia a velocità 0,75×, fai shadowing frase per frase e torna alla velocità normale quando diventa facile.
- Registrati e confronta con l’originale, facendo attenzione a parole come clock, frequency, laser.
Cos'è la tecnica dello Shadowing?
Shadowing è una tecnica di apprendimento delle lingue supportata da studi scientifici, originariamente sviluppata per la formazione dei traduttori professionisti e resa popolare dal poliglotta Dr. Alexander Arguelles. Il metodo è semplice ma potente: ascolti un audio in inglese di madrelingua e lo ripeti immediatamente ad alta voce — come un'ombra che segue il parlante con un ritardo di solo 1–2 secondi. A differenza dell'ascolto passivo o degli esercizi di grammatica, lo shadowing costringe il tuo cervello e i muscoli della bocca a elaborare e riprodurre simultaneamente i modelli di discorso reale. La ricerca dimostra che migliora significativamente la precisione della pronuncia, l'intonazione, il ritmo, il discorso connesso, la comprensione dell'ascolto e la fluidità del parlato — rendendolo uno dei metodi più efficaci per la preparazione alla prova di speaking dell'IELTS e per la comunicazione reale in inglese.