裸奇點(Naked singularity)存在嗎？

裸奇點是指未被事件視界包圍，可以被直接觀測到的奇點。

奇點是物理計算中存在的東西，而對於視界就摸稜兩可了。

先來談談黑洞是如何形成的吧:Massive stars having exhausted the fuel that sustained it
for millions of years, the star is no longer able to
hold itself up under its own weight, and it starts
collapsing catastrophically.

However a star with relativistic relation between density and pressure could collapse to a naked singularity.

為什麼我們需要視界呢？原因其一是Cosmic Censorship Hypothesis， 阻止了觀看者直接看到奇點。我們無法預測奇點會對宇宙產生什麼影響，以及當物質被吸進去的時候會發生什麼，所以視界將這些充滿不確定性的範圍給『包了』起來。視界將所有東西都吸了進去，即使光，所以我們無法直接看到它。裸奇點就不同了，它像黑洞一樣可以吸進東西，但也可以吐出來，所以我們是可以看到它的。你這個問題其實就等於在問奇點能不能被我們肉眼看見。而且如果裸奇點存在的話，black hole information paradox就隨著視界不見了。很多paradox都是因為視界而有的。目前還沒有實據證明裸奇點的存在，以下是some observations to look for that could prove the existence of naked singularity:

• High-energy explosions that
  produce naked singularities
  would brighten and fade in
  a distinctive way.
• Certain classes of gamma-ray
  bursts remain unexplained;
  naked singularities might
  account for them.
• Naked singularities would bend
  the light of background stars
  differently than black holes do.
• If a suspected black hole is
  spinning faster than a certain
  rate (which depends on its
  mass), it must actually be a
  naked singularity. The planned
  Square Kilometer Array (SKA)
  radio telescope would have
  the requisite precision to tell.

http://www.selmacyoushondar.com/attachments/article/30/P.S.Joshi%20-%20Naked%20Singularities.pdf

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再加一點， 裸奇點是現在霍金（ Stephen Hawking）和索恩（Kip Thorne）的新一輪賭注。之前霍金賭Cygnus X-1不是黑洞，他輸了。現在他賭大自然憎惡裸奇點，不知道這次結果會如何呢。