Shadowing Practice: 10 things you should know about black holes - Learn English Speaking with Video
בחר מצב תרגול
כל מצב פותח חדר תרגול במסך מלא.
134 משפטים
אם המשפטים קצרים או ארוכים מדי, לחץ על ערוך כדי להתאים אותם.
1
When I first learned about black holes, I was scared that one would fly through our solar system and eat us all up.
2
That was 30 years ago.
3
I'm not afraid of black holes anymore, but I am afraid that they have been misunderstood.
4
So here are 10 things that you should know about black holes.
5
First things first, what is a black hole?
6
A black hole contains a region from which nothing can ever escape,
7
because to escape you would have to move faster than the speed of light, which you can't.
8
The boundary of the region from which you cannot escape is called the horizon.
9
In the simplest case, the horizon has the form of a sphere.
10
Its radius is known as the Schwarzschild radius, named after Karl Schwarzschild, who first derived black holes as a solution to Einstein's general relativity.
11
How large are black holes?
12
The diameter of a black hole is directly proportional to the mass of the black hole.
13
So the more mass falls into the black hole, the larger the black hole becomes.
14
Compared to other stellar objects though, black holes are tiny because enormous gravitational pressure has compressed their mass into a very small volume.
15
For example, the radius of a black hole with the mass of planet
16
Earth is only a few millimeters.
17
What happens at the horizon?
18
A black hole horizon does not have substance.
19
Therefore, someone crossing the black hole horizon does not notice anything weird going on in their immediate surroundings.
20
This follows from Einstein's equivalence principle, which implies that in your immediate surrounding you cannot tell the difference between acceleration in flat space
21
and curved space that gives rise to gravity.
22
However, an observer far away from a black hole who watches somebody fall in would notice
23
that the infalling person seems to move slower and slower the closer they get to the horizon.
24
It appears this way because time close by the black hole horizon runs much slower than far away from the horizon.
25
That's one of these odd consequences of the relativity of time that Einstein discovered.
26
So, if you fall into a black hole, it only takes a finite amount of time to cross the horizon,
27
but from the outside it looks like it takes forever.
28
What you would experience at the horizon depends on the tidal force of the gravitational field.
29
The tidal force is, loosely speaking, the change of the gravitational force.
30
It's not the gravitational force itself, it's the difference between the gravitational forces at two nearby places, say at your head and at your feet.
31
The tidal force at the horizon is inversely proportional to the square of the mass of the black hole.
32
This means the larger and more mass of the black hole, the smaller the tidal force at the horizon.
33
Yes, you heard that right.
34
The larger the black hole, the smaller the tidal force at the horizon.
35
Therefore, if the black hole is only massive enough, you can cross the horizon without noticing what just happened.
36
And once you have crossed the horizon, there is no turning back.
37
The stretching from the tidal force will become increasingly unpleasant as you approach the center of the black hole.
38
Eventually it will rip everything apart.
39
In the early days of general relativity, many physicists believed that there is a singularity at the horizon,
40
but this turned out to be a mathematical mistake.
41
What is inside a black hole?
42
Nobody really knows.
43
General relativity predicts that inside the black hole is a singularity, that's a place where the tidal forces become infinitely large.
44
But we know that general relativity does not work nearby the singularity, because there the quantum fluctuations of space and time become very large.
45
To be able to tell what is inside a black hole, we would need a theory of quantum gravity.
46
And we don't have one.
47
Most physicists believe that such a theory, if we had it, would replace the singularity with something else.
48
How do black holes form?
49
We presently know of four different ways that black holes may form.
50
The best understood one is stellar collapse.
51
A sufficiently large star will form a black hole after its nuclear fusion runs dry,
52
which happens when the star has fused everything that could be fused.
53
Now, when the pressure generated by the fusion stops, the matter starts falling towards its own gravitational center,
54
and thereby it becomes increasingly dense.
55
Eventually the matter is so dense that nothing can overcome the gravitational pull on the surface of the star.
56
That's when a black hole has been created.
57
These black holes are called solar mass black holes, and they are the most common ones.
58
The next common type of black holes are the supermassive black holes that can be found in the centers of many galaxies.
59
Supermassive black holes have masses about a billion times that of solar mass black holes, and sometimes even more.
60
Exactly how they form is still not entirely clear.
61
Many astrophysicists think that supermassive black holes start out as solar mass black holes, and, because they sit in densely populated galactic centers,
62
they swallow a lot of other stars and grow.
63
However, it seems that the black holes grow faster than this simple idea suggests
64
and exactly how they manage to do that is not well understood.
65
A more controversial idea are primordial black holes.
66
These are black holes that might have formed in the early universe by large density fluctuations in the plasma.
67
So, they would have been there all along.
68
Primordial black holes can in principle have any mass.
69
While this is possible, it is difficult to find a model that produces primordial black holes without producing too many of them,
70
which is in conflict with observation.
71
Finally, there is the very speculative idea that tiny black holes could form in particle colliders.
72
This can only happen if our universe has additional dimensions of space, insofar there has not been any observational evidence that this might be the case.
73
How do we know black holes exist?
74
We have a lot of observational evidence that speaks for very compact objects with large masses that do not emit light.
75
These objects reveal themselves by their gravitational pull.
76
They do this, for example, by influencing the motion of other stars or gas clouds around them, which we have observed.
77
We furthermore know that these objects do not have a surface.
78
We know this
79
because matter falling onto an object with a surface would cause
80
more emission of particles than matter falling through a horizon and then just vanishing.
81
And since most recently, we have the observation from the Event Horizon Telescope, world, which is an image of the black hole shadow.
82
This is basically an extreme gravitational lensing event.
83
All these observations are compatible with the explanation that they are caused by black holes, and no similarly good alternative explanation exists.
84
Why did Hawking once say that black holes don't exist?
85
Hawking was using a very strict mathematical definition of black holes, and one that is rather uncommon among physicists.
86
If the inside of the black hole horizon remains disconnected forever, we speak of an event horizon.
87
If the inside is only disconnected temporarily, we speak of an apparent horizon.
88
But since an apparent horizon could be present for a very long time, like billions of billions of years,
89
the two types of horizons cannot be told apart by observation.
90
Therefore, physicists normally refer to both cases as black holes.
91
The more mathematically inclined people, however, count only the first case with an eternal event horizon as black hole.
92
What Hawking meant is that black holes may not have an eternal event horizon, but only a temporary, apparent horizon.
93
This is not a controversial position to hold, and one that is shared by many people in the field, including me.
94
For all practical purposes though, the distinction that Hawking drew is irrelevant.
95
How can black holes emit radiation?
96
Black holes can emit radiation
97
because the dynamical space -time of the collapsing black hole changes the notion of what a particle is.
98
This is another example of the relativity in Einstein's theory.
99
Just like time passes differently for different observers depending on where they are and how they move.
100
The notion of particles, too, depends on the observer and on where they are and how they move.
101
Because of this, an observer who falls into a black hole thinks that he is falling in vacuum.
102
But an observer far away from the black hole thinks that it is not vacuum but full of particles.
103
And where do the particles come from?
104
They come from the black hole.
105
This radiation that black holes emit is called Hawking radiation, because Hawking was the first to derive that this should happen.
106
The radiation has a temperature which is inversely proportional to the black hole's mass.
107
So, the smaller the black hole, the hotter it is.
108
For the stellar and supermassive black holes that we know of,
109
the temperature is well below the temperature of the cosmic microwave background and cannot be observed.
110
What is the information loss paradox?
111
The information loss paradox is caused by the emission of Hawking radiation.
112
This happens because Hawking radiation is purely thermal, which means it is random, except for having a specific temperature.
113
In particular, the radiation does not contain any information about what formed the black hole.
114
But while the black hole emits radiation, it loses mass and shrinks.
115
So, eventually the black hole will be entirely gone,
116
and all you are left with is this random radiation which depends only on the initial mass of the black hole.
117
It does not at all depend on the details of the matter that formed the black hole or whatever fell in later.
118
Therefore, if one only knows the final state of the evaporation, one cannot tell what formed the black hole.
119
Such a process is called irreversible, and the trouble is that there are no such processes in quantum theory.
120
Black hole evaporation radiation therefore is inconsistent with quantum theory as we know it, and something has to give.
121
Somehow this inconsistency has to be removed.
122
Most physicists believe that the solution is that the Hawking radiation somehow must contain information after all.
123
So will a black hole come and eat us all up?
124
It's not impossible, but very unlikely.
125
Most Most stellar objects in galaxies orbit around the galactic center because of the way that galaxies form.
126
It happens on occasion that two solar systems collide and a star
127
or planet or black hole is kicked onto a strange orbit,
128
leaves one solar system, and travels around until it gets caught up in the gravitational field of some other system.
129
But the stellar objects in galaxies are generally far apart from each other,
130
and we sit in an outer arm of a spiral galaxy where there isn't all that much going on.
131
So, it's exceedingly improbable that a black hole would come by on just exactly the right path to cause us trouble.
132
We would also know of this long in advance, because we would see the gravitational pull of the black hole acting on the outer planets.
133
If you have any questions about black holes that this video did not answer, please leave me a comment.
134
And don't forget to subscribe.
הורד אפליקציה
כל מה שאתה צריך כדי לדבר בשטף
הגיית AIציון לכל משפט
תרגול IPAשלוט בכל צליל
אוצר מיליםבנה את מאגר המילים שלך
משחק אוצר מיליםלמד תוך כדי משחק
אותו ערוץ
C1Mathematician Collapses All Functions to One Weird Formula
Daily ConversationUniversity StudentsWorking Adults
C13
AI Will End Philosophy, Physicist Claims
Daily ConversationUniversity StudentsWorking Adults
C19
Does God exist? Science does not have an answer.
Daily ConversationUniversity StudentsWorking Adults
C11
Has quantum mechanics proved that reality does not exist?
Daily ConversationUniversity StudentsWorking Adults
C1The Uncertainty Principle: What Does It Mean, How Does It Work?
Daily ConversationUniversity StudentsWorking Adults
C17
Superfluid Dark Matter
Daily ConversationUniversity StudentsWorking Adults
C11
We Can Now Simulate a Human Brain, Scientists Show
Daily ConversationUniversity StudentsWorking Adults
C15
Make AI Believe in God to Keep Humans Safe, Scientist Argues
Daily ConversationUniversity StudentsWorking Adults
C15
What is time?
IELTS PrepTOEFL PrepUniversity Students
C11
The End of Human Mathematics? AI's Recent Breakthrough -- And What's Next
Daily ConversationUniversity StudentsWorking Adults
C14
FINALLY: A Proof that Particles Take All Paths At Once?
Daily ConversationUniversity StudentsWorking Adults
C1Plastic Isn’t The Problem You’ve Been Made To Believe
Daily ConversationUniversity StudentsWorking Adults
C1Our Solar System Lost Two Planets!
Daily ConversationUniversity StudentsWorking Adults
B2I was SO wrong about quantum computing.
Daily ConversationUniversity StudentsWorking Adults
FOR YOU
המלץ על סרטון
C11
440 משפטים
White holes and wormholes are probably real. Here's why.
Daily ConversationUniversity Students
C11
207 משפטים
Was wäre, wenn diese Exoplaneten um unsere Sonne kreisen würden?
Daily ConversationUniversity Students
C12
187 משפטים
Hellraiser, Bataille and Limit Experiences
Daily ConversationUniversity Students
C11
23 משפטים
Black Hole Documentary 2019 - Part 1
Daily ConversationUniversity StudentsWorking Adults
C1101 משפטים
Two Different Things Are Killing Sharks
Daily ConversationUniversity Students
C11
105 משפטים
What If Humanity Became Type 7 Civilization?
Daily ConversationUniversity StudentsWorking Adults
C12
172 משפטים
Introduction to Astronomy: Crash Course Astronomy #1
Daily ConversationUniversity Students
C11
95 משפטים
What Happens When You Die?
Daily ConversationUniversity StudentsWorking Adults
C13
279 משפטים
LET THERE BE... Voltage? | Maxwell's Equation #2 Explained for Beginners
Daily ConversationUniversity Students
C1370 משפטים
Are We Living Inside an Alien Control System?
Daily ConversationUniversity StudentsWorking Adults
C185
66 משפטים
What science can’t answer, according to physicist Jim Al-Khalili | Big Think
Daily ConversationUniversity StudentsWorking Adults
C15
147 משפטים
We Traveled Back in Time. Now Physicists Are Angry.
Daily ConversationUniversity StudentsWorking Adults
אוצר מילים והערות הגייה לשיעור הזה
שיעור הדיבור הזה ברמה C1 מבוסס על הסרטון “10 things you should know about black holes”. המילים שחוזרות הכי הרבה: hole, horizon, mass, radiation, gravitational. בסרטון הזה יש 134 משפטים ו-1900 מילים לתרגול Shadowing. הדיבור נמשך 12:13. הדובר מדבר בקצב טבעי של כ-156 מילים בדקה, קרוב לשיחה יומיומית. רק 80% מהמילים נמצאות בין 3,000 המילים הנפוצות ביותר באנגלית, כך שאוצר המילים מאתגר.
אוצר מילים מרכזי בסרטון הזה
15 המילים המתקדמות ביותר בסרטון, עם ההגייה והמשמעות שלהן:
| מילה | הגייה | משמעות |
|---|---|---|
| horizon שם עצם | /həˈɹaɪ.zən/ | אופק \ אֹפֶק |
| particle שם עצם | /ˈpɑɹtək(ə)l/ | חֶלְקִיק, גַרגִיר |
| physicist שם עצם | /ˈfɪzɪsɪst/ | פִיזִיקַאי |
| quantum שם עצם | /ˈkwɑntəm/ | קְוַנְט |
| primordial שם תואר | /pɹaɪˈmɔɹ.di.əl/ | בְּרֵאשִׁיתִי |
| disconnect פועל | /dɪskəˈnɛkt/ | ניתק |
| paradox שם עצם | /ˈpæ.ɹəˌdɒks/ | פרדוקס |
| dense שם תואר | /ˈdɛns/ | עבות \ עָבֹת |
| orbit שם עצם | /ˈɔɹ.bɪt/ | מַסְלוּל |
| mathematical שם תואר | /ˌmæθ(.ə)ˈmæt.ɪ.kəl/ | מָתֵמָטִי |
| vacuum שם עצם | /ˈvæ.kjuːm/ | ואקום, ריק |
| collide פועל | /kəˈlaɪd/ | הִתְנַגֵּשׁ |
| acceleration שם עצם | /əkˌsɛl.əˈɹeɪ.ʃən/ | האצה |
| cosmic שם תואר | /ˈkɑz.mɪk/ | קוֹסְמִי |
| surroundings שם עצם | /səˈɹaʊndɪŋz/ | סְבִיבָה |
דקדוק בסרטון הזה
המבנים שהדובר משתמש בהם הכי הרבה, עם המילים המדויקות מהסרטון:
| מבנה | בסרטון |
|---|---|
| סביל (Passive voice) be + past participle — הדגש הוא על מה שקורה, לא על מי שעושה את הפעולה | have been misunderstood · is called · is known |
| הווה מושלם (Present perfect) have/has + past participle — פעולה שקרתה בעבר ועדיין יש לה חשיבות או השפעה עכשיו | have been misunderstood · has compressed · have crossed |
| משפטי זיקה (Relative clauses) who / which + clause — מידע נוסף על אדם או דבר | world, which is · one that is · temperature which is |
הגייה ששווה לשים לב אליה
הדובר משתמש ב-6 קיצורים וצורות מקוצרות, כמו don't, can't, I'm. אמרו אותם בצורה הקצרה, כפי שאתם שומעים אותם.
- הצלילים של “th”: mathematical /ˌmæθ(.ə)ˈmæt.ɪ.kəl/, thereby /ðɛɹˈbaɪ/, thermal /ˈθɜːməl/
- הצלילים של “sh” ו-“zh”: gravitational /ˌɡɹævɪˈteɪʃənəl/, evaporation /ɪˌvæpəˈɹeɪʃən/, fluctuation /flʌkt͡ʃuːˈeɪʃən/, observational /ˌɑbzɚˈveɪʃənəl/, emission /ɪˈmɪʃ.ən/
- מילים ארוכות — שימו לב להטעמה: gravitational /ˌɡɹævɪˈteɪʃənəl/, relativity /ɹɛl.əˈtɪv.ɪ.ti/, singularity /ˌsɪŋɡjəˈlæɹətɪ/, primordial /pɹaɪˈmɔɹ.di.əl/, evaporation /ɪˌvæpəˈɹeɪʃən/
צלילים שדוברי עברית מתקשים בהם:
- /w/ — שפתיים מעוגלות, לא /v/: quantum /ˈkwɑntəm/, equivalence /ɪˈkwɪv.ə.ləns/, microwave /ˈmaɪkɹoʊˌweɪv/, swallow /ˈswɑ.loʊ/, consequence /ˈkɑn.sɪ.kwəns/
- /æ/ — פתוח יותר מה-“אֶ” העברית, לא כמו “a” ב-“cup”: gravitational /ˌɡɹævɪˈteɪʃənəl/, singularity /ˌsɪŋɡjəˈlæɹətɪ/, evaporation /ɪˌvæpəˈɹeɪʃən/, galactic /ɡəˈlæktɪk/, paradox /ˈpæ.ɹəˌdɒks/
- /r/ — הלשון לא נוגעת בשום מקום, לא ה-“ר” הגרונית: horizon /həˈɹaɪ.zən/, gravitational /ˌɡɹævɪˈteɪʃənəl/, relativity /ɹɛl.əˈtɪv.ɪ.ti/, particle /ˈpɑɹtək(ə)l/, stellar /ˈstɛl.əɹ/
איך לתרגל עם הסרטון הזה
- הקשיבו לכל הסרטון פעם אחת בלי לדבר, ורשמו את המילים שאתם לא מכירים.
- התחילו במהירות 0.75×, תרגלו Shadowing משפט אחר משפט, וחזרו למהירות רגילה כשזה מרגיש קל.
- הקליטו את עצמכם והשוו למקור, תוך תשומת לב למילים כמו horizon, particle, physicist.
מהי טכניקת השאדואינג?
שאדואינג היא טכניקת למידת שפה מבוססת מדע שפותחה במקור להכשרת מתורגמנים מקצועיים ופופולרית על ידי הפוליגלוט ד"ר אלכסנדר ארגואלס. השיטה פשוטה אך עוצמתית: אתה מקשיב לאודיו באנגלית ילידית וחוזר עליו בקול רם מיד — כמו צל העוקב אחרי הדובר עם עיכוב של 1–2 שניות בלבד. בניגוד להאזנה פסיבית או תרגילי דקדוק, שאדואינג מכריח את המוח והשרירים בפה לעבד ולשחזר דפוסי דיבור אמיתיים בו זמנית. מחקרים מראים שזה משפר משמעותית את דיוק ההגייה, האינטונציה, הקצב, הדיבור המחובר, הבנת השמיעה ושטף הדיבור — מה שהופך אותו לאחת השיטות היעילות ביותר להכנה לIELTS Speaking ולתקשורת באנגלית בעולם האמיתי.