​来自15亿光年外的“问候”真的出自外星人吗？

来自15亿光年外的“问候”真的出自外星人吗？

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我们是兼职在辟谣，别人是全职在传播伪科学。”

——李治中（笔名菠萝），科普作家

这两天，一篇名为《外媒炸裂！真是外星人？宇宙深处神秘信号到底要不要回应？》的自媒体文章在网上广泛传播。不明真相的吃瓜群众纷纷震惊，难道《三体》终将从科幻变为现实？

简要来说，这篇文章依据的是英国《自然》杂志在9日发表的两篇天文学论文。

天文学家通过加拿大CHIME天文望远镜，在两个月内捕获到13个快速射电暴(Fast Radio Burst，简称FRBs)，其中有一个很不同寻常的重复电波，这个电波来自15亿光年外，也就是说，来自银河系外。

并且这次监测到的快速射电暴，频率出现在400MHz以下，打破了先前在2012年监测到的快速射电暴700MHz的记录。这将极大促进天文学家理解这种神秘河外射电束。

Astronomers in Canada have detected a mysterious volley of radio waves from far outside our galaxy, according to two studies published Wednesday in Nature.

What corner of the universe these powerful waves come from and the forces that produced them remain unknown.

The so-called repeating fast radio bursts were identified during the trial run last summer of a built-for-purpose telescope running at only a fraction of its capacity.

Known by its acronym CHIME, the world's most powerful radio telescope – spread across an area as big as a football pitch – is poised to detect many more of the enigmatic pulses now that it is fully operational.

至于这段神秘电波出自谁手，《卫报》、《今日美国》等媒体直接在标题中点出了“外星人”字眼。

也有科学家表示，不能排除本次监测的这一电波是来自外星宇宙飞船的可能性。

快速射电暴的首次发现可以追溯到2007年，但一般这种电波只出现一次，直到2012年人类才发现首例重复快速射电暴。迄今为止，我们总共才掌握了60多个快速射电暴的案例。

More than 60 bursts have been cataloged since 2007, but only one other – observed in 2012 at the Arecibo Observatory in Puerto Rico – was a repeater.

Obviously, the 2012 and 2018 "repeaters" have strikingly similar properties.

然而有的自媒体就在这段发现史上大做文章，展开了丰富的联想，杜撰出一个令人胆寒的外星文明。引导读者将一个具有新闻价值的重要天文发现用“外星人”来解释，从而满足他们的猎奇心理。

推论一

“目前观测到的信号数据越来越近“

“还记得2011年的60亿光年吗？还记得2012年的30亿光年吗？而2018年却只有15亿光年？……什么样的文明能够短短几年时间就飞跃几十亿光年的距离？”

事实：根据两例重复快速射电暴的坐标便可击穿谣言。FRB 121102的坐标是赤经05h32m、赤纬 +33°，FRB 180814的坐标是赤经04h22m、赤纬+73，角距相差40多度，显然是两个不同的源。如果硬要说两个快速射电暴来源于同一个宇宙飞船舰队，根据坐标计算，外星人的移动距离是21亿光年，而非15亿光年。

推论二

“低频就是飞行器发出的信号”

“根据我们人类的经验，1400往往是地面塔台发出的信号，而低于800的，甚至低到400，往往就不是地面设备发出的信号，而是飞行器发出的信号！……难道有外星文明在几年前通过探测发现了我们？继而派出了飞船？”

事实：低频可能是飞行器发出的信号，但不意味着“全盘肯定。”由于400MHz在地球上广泛用于无线电通信，对天文观测干扰极大，而天体的射电辐射往往频率较高，因此低频段的观测本来就不多。另一方面，400MHz是CHIME天线观测频率下限，因此本次发现不仅证明FRB的频率可以很低，而且也不排除可以更低。再者说，没有证据，全凭地球人的常识和规则去思考宇宙中的未知事物，这又是否合理呢？

神秘电波的信号源到底是啥？

快速射电暴在短短几毫秒内，就能释放极大的能量。高能天体物理学家王善钦说这种能量“远远超过地球上所有核武器同时爆炸产生的能量。”

Fast radio bursts (FRBs) flash only for a micro-instant, but can emit as much energy as the Sun does in 10,000 years.

Exactly what causes these high-energy surges of long waves at the far end of the electromagnetic spectrum remains the subject of intense debate.

BBC列举了5个可能的信号源：快速旋转的中子星(A rapidly spinning neutron star)，中子星相撞(Two stars merging)，高能量脉冲射电源被黑洞吞噬的现象(Blitzar)，黑洞(Black hole)和外星生命体(Alien life form)。

"FRBs, it seems, are likely generated in dense, turbulent regions of host galaxies," Shriharsh Tendulkar, a corresponding author for both studies and an astronomer at McGill University, told AFP.

Cosmic convulsions created by the turbulent gas clouds that give rise to stars, or stellar explosions such a supernovae, are both possible incubators.

But consecutive radio bursts are a special case.

Could these enigmatic radio pulses point to intelligence elsewhere in the Universe? Might they be messages in a bottle?

"It is extremely, extremely unlikely," said Tendulkar. "As a scientist I can't rule it out 100 percent. But intelligent life is not on the minds of any astronomer as a source of these FRBs."

如果是外星人，该回应吗？

If there are aliens who are sending the mysterious signals, should humans respond? Netizens from around the world shared their views. Liu Cixin, a Chinese science fiction writer known for his “Three-Body Problem” trilogy, told Pear Video that “We should be careful.”

有网友说应该回应

有人说不应该

海外网友也对此次发现展开了激烈讨论

对此，科幻作家刘慈欣说

但是，即便公众对外星人有着强烈兴趣，电波信号源自外星人的可能性非常小。专家们表示，此前很多类似电波都被证明是自然现象。至于现在的未知，还需要学者进一步跟踪观察，或许在不远的未来我们能够得知真相。

文章部分引用腾讯科技、天文茶餐厅