Can you solve the time travel riddle? - Dan Finkel

3,516,005 views ใƒป 2018-12-04

TED-Ed


์•„๋ž˜ ์˜๋ฌธ์ž๋ง‰์„ ๋”๋ธ”ํด๋ฆญํ•˜์‹œ๋ฉด ์˜์ƒ์ด ์žฌ์ƒ๋ฉ๋‹ˆ๋‹ค.

๋ฒˆ์—ญ: Tae Han Yoon ๊ฒ€ํ† : Won Jang
00:07
Your internship in Professor Ramseyโ€™s physics lab has been amazing.
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๋žจ์ง€ ๊ต์ˆ˜์˜ ๋ฌผ๋ฆฌ์—ฐ๊ตฌ์‹ค์˜ ๋‹น์‹ ์˜ ์ธํ„ด์‹ญ์€ ์ •๋ง ํ›Œ๋ฅญํ–ˆ์Šต๋‹ˆ๋‹ค.
00:11
Until, that is, the professor accidentally stepped through a time portal.
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๊ต์ˆ˜๊ฐ€ ์šฐ์—ฐํžˆ ํƒ€์ž„ ํฌํ„ธ์— ๋“ค์–ด๊ฐ€๊ธฐ ์ „๊นŒ์ง€๋Š”์š”.
00:16
Youโ€™ve got just a minute to jump through the portal to save him before it closes
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๋‹น์‹ ์ด ํฌํ„ธ์ด ๋‹ซํžˆ๊ธฐ ์ „ 1๋ถ„๋‚ด์— ํฌํ„ธ๋กœ ๋›ฐ์–ด๋“ค์–ด ๊ทธ๋ฅผ ๊ตฌํ•˜์ง€ ์•Š์œผ๋ฉด
00:20
and leaves him stranded in history.
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๊ทธ๋Š” ์—ญ์‚ฌ์†์— ๊ฐ‡ํžˆ๊ฒŒ ๋  ๊ฒƒ ์ž…๋‹ˆ๋‹ค.
00:23
Once youโ€™re through it, the portal will close,
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์ผ๋‹จ ๋“ค์–ด๊ฐ€๋ฉด ํฌํ„ธ์€ ๋‹ซํžˆ๊ณ 
00:25
and your only way back will be to create a new one
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๋‹ค์‹œ ๋Œ์•„์˜ค๊ธฐ ์œ„ํ•ด์„  ์—ฐ๊ตฌ์‹ค์—์„œ ๊ฐ€์ ธ์˜จ ํฌ๋กœ๋…ธ ๋…ธ๋“ˆ๋กœ
00:29
using the chrono-nodules from your lab.
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์ƒˆ ํฌํ„ธ์„ ์—ด์–ด์•ผ๋งŒ ํ•ฉ๋‹ˆ๋‹ค.
00:32
Activated nodules connect to each other
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ํ™œ์„ฑํ™”๋œ ๋…ธ๋“ˆ์€
๋นจ๊ฐ„์ƒ‰์ด๋‚˜ ํŒŒ๋ž€์ƒ‰ ํƒ€ํ‚ค์˜จ ์–ฝํž˜์„ ํ†ตํ•ด ์„œ๋กœ ์—ฐ๊ฒฐ๋˜์–ด ์žˆ์Šต๋‹ˆ๋‹ค.
00:34
via red or blue tachyon entanglement.
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00:38
Activate more nodules and theyโ€™ll connect
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๋” ๋งŽ์€ ๋…ธ๋“ˆ์„ ํ™œ์„ฑํ™”ํ•˜๋ฉด
00:40
to all other nodules in the area.
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๊ทธ ๊ตฌ์—ญ์— ์žˆ๋Š” ๋‹ค๋ฅธ ๋ชจ๋“  ๋…ธ๋“ˆ๊ณผ ์—ฐ๊ฒฐ์ด ๋ฉ๋‹ˆ๋‹ค.
00:43
As soon as a red or blue triangle is created with a nodule at each point,
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๊ฐ ์ง€์ ์˜ ๋…ธ๋“ˆ์ด ์—ฐ๊ฒฐ๋ผ ๋นจ๊ฐ„์ƒ‰์ด๋‚˜ ํŒŒ๋ž€์ƒ‰ ์‚ผ๊ฐํ˜•์ด ๋งŒ๋“ค์–ด์ง€๋ฉด
00:48
it opens a doorway through time that will take you back to the present.
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ํ˜„์žฌ๋กœ ๋Œ์•„์˜ฌ ์ˆ˜ ์žˆ๋Š” ์ฐจ์›๋ฌธ์ด ์—ด๋ฆฌ๊ฒŒ ๋ฉ๋‹ˆ๋‹ค.
00:53
But the color of each individual connection manifests at random,
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ํ•˜์ง€๋งŒ ๊ฐ ์—ฐ๊ฒฐ์˜ ์ƒ‰์€ ๋ฌด์ž‘์œ„๋กœ ๋‚˜์˜ค๊ณ 
00:58
and thereโ€™s no way to choose or change its color.
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๊ทธ๊ฒƒ์„ ์„ ํƒํ•˜๊ฑฐ๋‚˜ ๋ฐ”๊ฟ€ ์ˆ˜๋„ ์—†์Šต๋‹ˆ๋‹ค.
01:02
And thereโ€™s one more problem:
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๊ทธ๋ฟ๋งŒ์ด ์•„๋‹™๋‹ˆ๋‹ค.
01:03
each individual nodule creates a temporal instability
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๊ฐ๊ฐ์˜ ๋…ธ๋“ˆ์€ ์‹œ๊ฐ„์  ๋ถˆ์•ˆ์ •์„ฑ์„ ํ˜•์„ฑํ•ด
01:08
that raises the chances the portal might collapse as you go through it.
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๋‹น์‹ ์ด ํ†ต๊ณผํ•  ๋•Œ ํฌํ„ธ์ด ๋ถ•๊ดดํ•  ํ™•๋ฅ ์„ ๋†’์ž…๋‹ˆ๋‹ค.
01:12
So the fewer you bring, the better.
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๊ทธ๋Ÿฌ๋ฏ€๋กœ ๋…ธ๋“ˆ์€ ์ ์„์ˆ˜๋ก ์ข‹์Šต๋‹ˆ๋‹ค.
01:15
The portalโ€™s about to close.
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ํฌํ„ธ์ด ๊ณง ๋‹ซํžˆ๋ ค๊ณ  ํ•ฉ๋‹ˆ๋‹ค.
01:17
Whatโ€™s the minimum number of nodules you need to bring
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๋นจ๊ฐ„์ƒ‰์ด๋‚˜ ํŒŒ๋ž€์ƒ‰ ์‚ผ๊ฐํ˜•์„ ๋งŒ๋“ค์–ด
01:20
to be certain youโ€™ll create a red or blue triangle and get back to the present?
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ํ˜„์žฌ๋กœ ๋Œ์•„์˜ค๋ ค๋ฉด ์ตœ์†Œ ๋ช‡ ๊ฐœ์˜ ๋…ธ๋“ˆ์ด ํ•„์š”ํ• ๊นŒ์š”?
01:24
Pause here if you want to figure it out for yourself!
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์Šค์Šค๋กœ ์ •๋‹ต์„ ์ฐพ๊ณ  ์‹ถ๋‹ค๋ฉด ์—ฌ๊ธฐ์„œ ์˜์ƒ์„ ์ •์ง€ํ•˜์„ธ์š”!
01:29
Answer in: 3
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3์ดˆ ํ›„ ์ •๋‹ต๊ณต๊ฐœ
01:31
Answer in: 2
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2์ดˆ ํ›„ ์ •๋‹ต๊ณต๊ฐœ
01:33
Answer in: 1
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1์ดˆ ํ›„ ์ •๋‹ต๊ณต๊ฐœ
01:34
This question is so rich that an entire branch of mathematics
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์ด ๋ฌธ์ œ๋Š” ์›Œ๋‚™ ํ•™๋ฌธ์  ๊ฐ€์น˜๊ฐ€ ๋†’์•„
๋žจ์ง€ ์ด๋ก ์ด๋ผ๋Š” ์ˆ˜ํ•™์˜ ํ•œ ๋ถ„์•ผ๋กœ๊นŒ์ง€ ๋ฐœ์ „ํ•˜๊ฒŒ ๋˜์—ˆ์Šต๋‹ˆ๋‹ค.
01:38
known as Ramsey Theory developed from it.
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01:41
Ramsey Theory is home to some famously difficult problems.
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๋žจ์ง€ ์ด๋ก ์€ ๋‚œํ•ดํ•˜๊ธฐ๋กœ ์œ ๋ช…ํ•œ ๋ช‡๋ช‡ ๋ฌธ์ œ๋“ค์˜ ์ถœ๋ฐœ์ ์ด๊ธฐ๋„ ํ•ฉ๋‹ˆ๋‹ค.
01:45
This one isnโ€™t easy, but it can be handled
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๋น„๋ก ์‰ฌ์šด ๋ฌธ์ œ๋Š” ์•„๋‹ˆ์ง€๋งŒ ์ฒด๊ณ„์ ์œผ๋กœ ์ ‘๊ทผํ•œ๋‹ค๋ฉด
01:48
if you approach it systematically.
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ํ•ด๊ฒฐํ•  ์ˆ˜ ์žˆ์Šต๋‹ˆ๋‹ค.
01:50
Imagine you brought just three nodules.
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๋…ธ๋“ˆ์„ ๋‹จ ์„ธ ๊ฐœ๋งŒ ๊ฐ€์ ธ์™”๋‹ค๊ณ  ๊ฐ€์ •ํ•ด ๋ด…์‹œ๋‹ค.
01:53
Would that be enough? No - for example, you might have two blue
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๊ทธ๊ฑฐ๋ฉด ์ถฉ๋ถ„ํ• ๊นŒ์š”? ์•„๋‹™๋‹ˆ๋‹ค. ์˜ˆ๋ฅผ ๋“ค์–ด ํŒŒ๋ž€์ƒ‰ ๋‘ ๊ฐœ์™€
01:57
and one red connection, and be stuck in the past forever.
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๋นจ๊ฐ„์ƒ‰ ํ•˜๋‚˜๋กœ ์—ฐ๊ฒฐ์ด ๋˜๋ฉด ์˜์›ํžˆ ๊ณผ๊ฑฐ์— ๊ฐ‡ํžˆ๊ณ  ๋ง๊ฒ ์ฃ .
02:01
Would four nodules be enough? No - there are many arrangements here
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๊ทธ๋Ÿผ ๋„ค ๊ฐœ๋ฉด ์ถฉ๋ถ„ํ• ๊นŒ์š”? ์•„๋‹ˆ์š”.
์•„์ง๋„ ๋งŽ์€ ๊ฒฝ์šฐ์˜ ์ˆ˜์—์„œ ํŒŒ๋ž€์ƒ‰์ด๋‚˜ ๋นจ๊ฐ„์ƒ‰ ์‚ผ๊ฐํ˜•์ด ๋งŒ๋“ค์–ด์ง€์ง€ ์•Š์Šต๋‹ˆ๋‹ค.
02:06
that donโ€™t give a blue or red triangle.
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02:09
What about five?
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๋‹ค์„ฏ ๊ฐœ๋Š” ์–ด๋–จ๊นŒ์š”?
02:10
It turns out there is an arrangement of connections
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ํŒŒ๋ž€์ƒ‰ ๋˜๋Š” ๋นจ๊ฐ„์ƒ‰ ์‚ผ๊ฐํ˜•์ด ์—†๋Š”
02:13
that avoids creating a blue or red triangle.
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์กฐํ•ฉ์ด ํ•˜๋‚˜๊ฐ€ ์žˆ๋„ค์š”.
02:16
These smaller triangles donโ€™t count because they donโ€™t have a nodule at each corner.
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์กฐ๊ทธ๋งŒ ์‚ผ๊ฐํ˜•๋“ค์€ ๊ผญ์ง“์ ์— ๋…ธ๋“ˆ์ด ์žˆ์ง€ ์•Š์œผ๋ฏ€๋กœ ํฌํ•จ๋˜์ง€ ์•Š์Šต๋‹ˆ๋‹ค.
02:22
However, six nodules will always create a blue triangle or a red triangle.
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ํ•˜์ง€๋งŒ ์—ฌ์„ฏ ๊ฐœ์˜ ๋…ธ๋“ˆ์€ ํ•ญ์ƒ ํŒŒ๋ž€์ƒ‰ ํ˜น์€ ๋นจ๊ฐ„์ƒ‰ ์‚ผ๊ฐํ˜•์„ ๋งŒ๋“ญ๋‹ˆ๋‹ค.
02:28
Hereโ€™s how we can prove that without sorting through every possible case.
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๋ชจ๋“  ๊ฒฝ์šฐ๋ฅผ ์ผ์ผ์ด ๋”ฐ์ ธ๋ณด์ง€ ์•Š๊ณ  ์ด๋ฅผ ์ฆ๋ช…ํ•˜๋Š” ๋ฐฉ๋ฒ•์€ ์ด๋ ‡์Šต๋‹ˆ๋‹ค.
02:32
Imagine activating the sixth nodule,
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์—ฌ์„ฏ ๋ฒˆ์งธ์˜ ๋…ธ๋“ˆ์„ ํ™œ์„ฑํ™”ํ•˜๋ฉด
02:35
and consider how it might connect to the other five.
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๋‹ค๋ฅธ ๋‹ค์„ฏ ๊ฐœ์™€ ์–ด๋–ป๊ฒŒ ์—ฐ๊ฒฐ์ด ๋ ์ง€ ์ƒ์ƒํ•ด๋ณด์„ธ์š”.
02:38
It could do so in one of six ways:
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์ด ์—ฌ์„ฏ ๊ฐ€์ง€์˜ ๊ฒฝ์šฐ๊ฐ€ ์žˆ์Šต๋‹ˆ๋‹ค:
02:41
with five red connections, five blue connections, or some mix of red and blue.
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๋‹ค์„ฏ ๊ฐœ์˜ ๋นจ๊ฐ„์ƒ‰์ด๋‚˜ ํŒŒ๋ž€์ƒ‰, ํ˜น์€ ๋นจ๊ฐ„์ƒ‰๊ณผ ํŒŒ๋ž€์ƒ‰์ด ์„ž์ด๋Š” ๊ฒฝ์šฐ์ฃ .
02:46
Notice that every possibility has at least three connections of the same color
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๊ทธ ์–ด๋Š ๊ฒฝ์šฐ์—๋„ ์ตœ์†Œํ•œ ์„ธ ๊ฐœ์˜ ์—ฐ๊ฒฐ์€ ๊ฐ™์€ ์ƒ‰์œผ๋กœ
02:51
coming from this nodule.
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์ด ๋…ธ๋“ˆ์— ์—ฐ๊ฒฐ๋ฉ๋‹ˆ๋‹ค.
02:53
Letโ€™s look at just the nodules on the other end
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์„ธ ๊ฐœ์˜ ๊ฐ™์€ ์ƒ‰ ์—ฐ๊ฒฐ์ด ๋งŒ๋“ค์–ด์ง„
02:56
of those same three color connections.
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๋ชจ๋“ˆ์„ ํ•œ ๋ฒˆ ์‚ดํŽด ๋ด…์‹œ๋‹ค.
02:58
If the connections were blue,
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๋งŒ์•ฝ์— ์—ฐ๊ฒฐ์ด ํŒŒ๋ž€์ƒ‰์ด๋ผ๋ฉด
03:00
then any additional blue connection between those three would give us a blue triangle.
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์ด ์„ธ ๋…ธ๋“ˆ ์‚ฌ์ด์˜ ์—ฐ๊ฒฐ์ด ๋‹จ ํ•˜๋‚˜๋ผ๋„ ํŒŒ๋ž€์ƒ‰์ด๋ฉด ํŒŒ๋ž€์ƒ‰ ์‚ผ๊ฐํ˜•์ด ์ƒ๊น๋‹ˆ๋‹ค.
03:05
So the only way we could get in trouble
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์ €ํฌ๊ฐ€ ๊ณค๋ž€ํ•ด์ง€๋Š” ๊ฒฝ์šฐ์˜ ์ˆ˜๋Š”
03:07
is if all the connections between them were red.
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์„ธ ๊ฐ€์ง€ ์—ฐ๊ฒฐ์ด ๋ชจ๋‘ ๋นจ๊ฐ„์ƒ‰์ธ ๊ฒฝ์šฐ๋ฐ–์— ์—†๊ฒ ์ง€์š”.
03:10
But those three red connections would give us a red triangle.
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ํ•˜์ง€๋งŒ ๊ทธ ๋นจ๊ฐ„์ƒ‰ ์—ฐ๊ฒฐ๋“ค์€ ๋นจ๊ฐ„์ƒ‰ ์‚ผ๊ฐํ˜•์„ ๋งŒ๋“ค๊ฒŒ ๋ฉ๋‹ˆ๋‹ค.
03:14
No matter what happens, weโ€™ll get a red or a blue triangle,
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๊ทธ ์–ด๋Š ๊ฒฝ์šฐ์—๋„ ๋นจ๊ฐ„์ƒ‰ ํ˜น์€ ํŒŒ๋ž€์ƒ‰ ์‚ผ๊ฐํ˜•๊ณผ ํ•จ๊ป˜
03:18
and open our doorway.
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์ฐจ์›๋ฌธ์ด ์—ด๋ฆฌ๊ฒ ๊ตฐ์š”.
03:20
On the other hand,
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๋ฐ˜๋ฉด์—
03:21
if the original three connections were all red instead of blue,
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๋งŒ์•ฝ ์›๋ž˜์˜ ํŒŒ๋ž€์ƒ‰ ์—ฐ๊ฒฐ์ด ๋นจ๊ฐ„์ƒ‰์ด์—ˆ๋‹ค๋ฉด
03:25
the same argument still works, with all the colors flipped.
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๊ทธ๋ƒฅ ์ƒ‰์ด ๋ฐ˜๋Œ€์ผ ๋ฟ, ๊ฐ™์€ ๋…ผ๋ฆฌ๊ฐ€ ์ ์šฉ๋ฉ๋‹ˆ๋‹ค.
03:29
In other words, no matter how the connections are colored,
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๋‹ค๋ฅธ ๋ง๋กœ ํ•˜์ž๋ฉด, ์—ฐ๊ฒฐ์ด ์–ด๋Š ์ƒ‰์ด๊ฑด ๊ฐ„์—
03:32
six nodules will always create a red or blue triangle and a doorway leading home.
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์—ฌ์„ฏ ๊ฐœ์˜ ๋…ธ๋“ˆ์€ ํ•ญ์ƒ ๋นจ๊ฐ„์ƒ‰ ํ˜น์€ ํŒŒ๋ž€์ƒ‰ ์‚ผ๊ฐํ˜•๊ณผ ์ฐจ์›๋ฌธ์„ ์ƒ์„ฑํ•ฉ๋‹ˆ๋‹ค.
03:38
So you grab six nodules and jump through the portal.
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๊ทธ๋Ÿฌ๋ฏ€๋กœ ์—ฌ์„ฏ ๊ฐœ์˜ ๋…ธ๋“ˆ์„ ์ง‘์–ด๋“ค๊ณ  ํฌํ„ธ๋กœ ๋›ฐ์–ด๋“œ์„ธ์š”.
03:41
You were hoping your internship would give you valuable life experience.
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์ธํ„ด์‹ญ์„ ํ†ตํ•ด ๊ท€์ค‘ํ•œ ์ธ์ƒ ๊ฒฝํ—˜์„ ์–ป๊ธฐ๋ฅผ ๋ฐ”๋ผ์…จ๊ฒ ์ง€์š”.
03:45
Turns out, that didnโ€™t take much time.
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๋ณด๊ธฐ๋ณด๋‹ค ๊ธˆ๋ฐฉ์ด์—ˆ๋„ค์š”.
์ด ์›น์‚ฌ์ดํŠธ ์ •๋ณด

์ด ์‚ฌ์ดํŠธ๋Š” ์˜์–ด ํ•™์Šต์— ์œ ์šฉํ•œ YouTube ๋™์˜์ƒ์„ ์†Œ๊ฐœํ•ฉ๋‹ˆ๋‹ค. ์ „ ์„ธ๊ณ„ ์ตœ๊ณ ์˜ ์„ ์ƒ๋‹˜๋“ค์ด ๊ฐ€๋ฅด์น˜๋Š” ์˜์–ด ์ˆ˜์—…์„ ๋ณด๊ฒŒ ๋  ๊ฒƒ์ž…๋‹ˆ๋‹ค. ๊ฐ ๋™์˜์ƒ ํŽ˜์ด์ง€์— ํ‘œ์‹œ๋˜๋Š” ์˜์–ด ์ž๋ง‰์„ ๋”๋ธ” ํด๋ฆญํ•˜๋ฉด ๊ทธ๊ณณ์—์„œ ๋™์˜์ƒ์ด ์žฌ์ƒ๋ฉ๋‹ˆ๋‹ค. ๋น„๋””์˜ค ์žฌ์ƒ์— ๋งž์ถฐ ์ž๋ง‰์ด ์Šคํฌ๋กค๋ฉ๋‹ˆ๋‹ค. ์˜๊ฒฌ์ด๋‚˜ ์š”์ฒญ์ด ์žˆ๋Š” ๊ฒฝ์šฐ ์ด ๋ฌธ์˜ ์–‘์‹์„ ์‚ฌ์šฉํ•˜์—ฌ ๋ฌธ์˜ํ•˜์‹ญ์‹œ์˜ค.

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