20、 Obama
Int 388113 Folder Collection
After playing the video, you can click or select the word to look it up in the dictionary.
Loading...
Report Subtitle Errors
Gravity. It controls the universe.
Everything attracts everything else.
Ouch!
Including you.
Ow!
In this final lesson,
we'll explore what gravity means for space-time,
or rather what space-time means for gravity.
Until now, we've been dealing with things moving at constant speeds,
with straight world lines in space-time.
But once you add gravity,
if you measure a speed at one moment,
then again a bit later,
the speed may have changed.
In other words, as I discovered, gravity causes acceleration,
so we need the world line to look different from one moment to the next.
As we saw in the last lesson,
the correct way to tilt an object's world line is using a Lorentz transformation:
Einstein's stretch and squash trick.
So, to map out what gravity is doing to Tom's motion,
we need to create a whole load of little patches of space-time,
each transformed by different amounts.
So that my world line is at a different angle in each one.
And then, we're ready to stitch everything together.
We assemble a cozy quilt of space-time
where world lines look curved.
Where the world lines join, the objects collide.
By making these connections between the patches,
a curvature gets built into space-time itself.
But Einstein's true genius
was to describe precisely how each patch is stretched and squashed
according to nearby mass and energy.
The mere presence of stuff curves the space-time,
and curving space-time moves the stuff around.
This is gravity, according to Einstein.
Previously, Isaac Newton had explained gravity using the ideas of force and acceleration,
without any wibbly wobbly space-time,
and that did pretty well.
But Einstein's theory does just slightly better at predicting,
for example, the orbit of Mercury around the Sun,
or the way that light rays are deflected by massive objects.
More importantly, Einstein's theory predicts things that simply don't exist in older theories
where space, time and gravity were separate.
The stitching can leave wrinkles in the space-time material.
These are called gravitational waves,
which should be detectable as tiny, repetitive, subtle squashes and stretches in space.
So we're building experiments to check if they are there.
In the meantime, indirect evidence,
most recently in the polarization patterns of light left over from the Big Bang,
strongly suggest that they are.
But despite Einstein's successes,
when too much stuff gets concentrated in too small a space,
like in a black hole,
the curvature of space-time becomes so large,
that his equations collapse.
We need a new picture of space-time that incorporates quantum mechanics
to unlock the secret at the heart of black holes.
Which means there's plenty more to be discovered about space, time, and space-time in the future.
    You must  Log in  to get the function.
Tip: Click on the article or the word in the subtitle to get translation quickly!

Loading…

Int

【TED-Ed】The fundamentals of space-time: Part 3 - Andrew Pontzen and Tom Whyntie

388113 Folder Collection
稲葉白兎 published on February 1, 2015

Learning Words

loading
More Recommended Videos

Comments

Loading…

  1. 1. Search word

    Select word on the caption to look it up in the dictionary!

  2. 2. Repeat single sentence

    Repeat the same sentence to enhance listening ability

  3. 3. Shortcut

    Shortcut!

  4. 4. Close caption

    Close the English caption

  5. 5. Embed

    Embed the video to your blog

  6. 6. Unfold

    Hide right panel

  1. Listening Quiz

    Listening Quiz!

  1. Click to open your notebook

  1. UrbanDictionary 俚語字典整合查詢。一般字典查詢不到你滿意的解譯，不妨使用「俚語字典」，或許會讓你有滿意的答案喔