If you believe in ghosts, you are far from alone.
如果你相信这个世界上有鬼，不用怕，因为世界上绝不止你一个人这样认为。
Around 45% of Americans believe in ghosts and as many as 18% of people will go so far as to say they have had contact with a ghost. I will also admit to spooking myself out on occasion when my dog has refused to stop barking at what appears to be an empty corner of the house.
根据数据统计，约45%的美国人相信鬼是真实存在的，还有18%的人甚至会宣称自己和鬼交流过。如果有一天我的宠物狗朝房间的空角落一直狂吠不止，我可能也会觉得有什么诡异的东西。
But what makes us feel like we are in the presence of a supernatural spirit?
但是到底是什么让我们觉得我们周边有超自然灵魂的存在？
Are there possible scientific explanations for that tingling sensation you get on the back of your neck, or the sudden feeling of uneasiness with an origin you can’t quite place?
我们有时候会有自己的后颈脖痒痒的感觉，或是突然没来由地觉得坐立不安，对于这些现象，是否可以从科学的角度来给予合理解释？
Let's investigate six possible explanations for that paranormal feeling that are rooted in science rather than the supernatural.
就让我们从下面六个科学角度来尝试解释那些诡异感觉，这些所谓的超自然背后也许也有着科学原因。
1、Low frequency sound
次声波
Just as the human eye can only see light at a range of frequencies—for example, we can't see radio waves—the human ear can only hear sounds in a range of frequencies.
就像人的眼睛只能看到某种范围内的光频一样——比如无线电波，人的耳朵也只能听见某种范围内的声频。
Above about 20,000 Hertz, sounds are too high pitched for our ears to parse them, like the echolocation calls of most bats that fall in this ultrasonic range.
人类无法接收超过两万赫兹的声音，因为音频过高，像大部分蝙蝠用来回声定位的声波就属于这种两万赫兹以上的超声波。
Similarly, human ears have trouble hearing low-frequency sounds below about 20 Hertz—known as infrasound—but such sounds do not go totally unnoticed.
同样道理，人类耳朵也无法接收低于20赫兹的低频声音——比如说大家所熟知的次声波，但是人类对于这种低频声音并不是完全无法接收。
In a 2003 study, 22% of concert goers who were exposed to sounds at 17 Hertz reported feeling or sorrowful, getting chills, or "nervous feelings of revulsion and fear."
2003年的一项研究表明22%的音乐会爱好者在17赫兹的低频环境中会觉得心神不宁或心生抑郁，甚至会觉得毛骨悚然，又或是产生“紧张、厌恶以及害怕的感觉”。
So what are some of the more ordinary origins of such low frequency sounds? Weather events like earthquakes and volcanic activity or lightning, and communication between animals including elephants, whales, and hippos can all produce infrasound.
所以这些低频声音一般都来源于什么地方呢？一些气候现象比如地震、火山运动和闪电，还有大象、鲸鱼和河马等动物之间的交流声音都会产生次声波。
And if you don’t live by any volcanoes or hippos but still think your house may be haunted? Humans also create low frequency sound via diesel engines, wind turbines, and some loud speakers or chemical explosions.
也许你住的地方既没有火山也没有河马，但你还是有鬼魂在身边游荡那种毛骨悚然的感觉。那是因为柴油机引擎、风涡轮以及一些扩音器、化学爆炸等人类活动的结果也会制造低频声音。
2、Mold
霉菌
Breathing in toxic mold can be bad for your respiratory system, but it can also be bad for your brain. Exposure to mold is known to cause neurologic symptoms like delirium, dementia, or irrational fears.
霉化环境会产生毒素，不仅对我们的呼吸系统有害，也影响着我们的大脑运作。正如大家所了解的，它会影响我们的神经系统，从而使我们出现神经错乱、痴呆或是神经质性恐惧等症状。
So is it a coincidence that the houses we suspect are haunted also tend to be in disrepair and so quite possibly full of toxic mold?
所以，当我们觉得屋子里有鬼时，会不会可能是由于房子年久失修而形成了有毒的霉化环境？
Scientists have worked to draw a firm link between the presence of mold and reported ghost sightings, but so far the evidence is mostly anecdotal.
科学家们也一直在研究霉化环境和有些人宣称的见鬼之间存在的有力联系，但是目前为止大部分证据仍然不具备足够的事实依据。
3、Carbon monoxide
一氧化碳
Just as breathing in mold could lead us to see, hear, and feel things that aren’t really there, so too can breathing in too much carbon monoxide. 、
就像呆在霉化环境能够让我们看到、听到、以及感觉到那些根本就不存在的东西一样，吸收过量的一氧化碳也会让我们产生这样的幻觉。
We have carbon monoxide detectors in our homes to make sure we are not breathing in this odorless, colorless gas that slowly poisons us while going undetected by our senses.
一氧化碳虽然无色无味，但是我们可以在家里安一个检测器，这样就可以避免我们在不知不觉的情况下呼吸过量的一氧化碳。
But before a carbon monoxide gas leak poisons us, it can cause auditory hallucinations, a feeling of pressure on your chest, and an “unexplained feeling of dread.”
但是在我们一氧化碳中毒之前，我们会先出现幻听、胸闷以及心悸等症状。
An often-told ghost story from the 1920s about the H family who moved into a new house only to hear footsteps, see apparitions, and feel malicious paranormal presences, turned out to be the result of carbon monoxide poisoning from a broken furnace.
人们津津乐道的那个关于上个世纪20年代H姓的鬼故事就是这样，说H一家搬进新房之后总会听见脚步声，看到幽灵，老是感觉有什么不干不净的恶灵存在，最后证明这一切的罪魁祸首是破旧老坏的壁炉释放的一氧化碳。
4、The power of suggestion
暗示的力量
Studies suggest that we are more likely to believe in a paranormal experience if someone else who was there can back up our belief.
研究表明，对于那些超自然经历，只要有人相信，我们自己也就会更确定它的真实性。
So while we might be able to convince ourselves that we were somehow mistaken about what we saw or heard, we tend to put more stock into someone else’s eye witness account if it also backs our suspicions. So our belief in ghosts can be catching.
因此，有时候原本我们告诉自己只是看错了或听错了，但是只要有人佐证了我们的怀疑，我们就会更倾向于相信别人的“眼见为实”。由此说来，我们对于鬼魂是否存在的态度是可以相互传染影响的。
Similarly, I would like to extend an apology to anyone I ever played the game of Ouija with as a kid.
我小时候曾经玩过笔仙一类的游戏，我想在这里对那些被我邀着玩这类游戏的小伙伴们表示一下我的歉意。
The toy game board used to contact spirits always proved too tempting to resist so the one moving it was always me, and not a paranormal spirit, even though I was just as excited as everyone else.
这种通灵的占卜类游戏对于儿时的我来说很是具有诱惑力，让人难以拒绝，所以转动占卜盘的那个人一直是我，当然从未出现什么魂灵，虽然我总是和其他小伙伴一样激动得不行。
5、Drafts
通风口
As the days get hotter and air conditioning becomes more and more expensive, I rely more on opening windows to cool my home.
天气现在越来越热，但是开空调的花销又越来越大，所以我经常开窗通风来给房间降温。
Opening windows on opposite ends of a room can create a nice breeze, but it can also create cold spots as air flow outside changes, causing cooler air to enter a warmer room.
打开对面尽头的窗户就有令人舒服的微风迎面扑来，但是由于室内外空气对流，房间里会出现相对低温的地方，让人觉得有点阴冷。
Drafts can also sneak in through chimneys and cause doors to slam or door knobs to rattle. So before you schedule a séance, try closing a few windows.
通风口也会渗过风，吹得门吱呀作响，或是门环啪嗒出声。如果你打算来个迎神会之类的，事先闭上一些窗户比较好。
6、We enjoy being afraid.
害怕并快乐
Neurologists have found that our brains release dopamine, a chemical associated with pleasure, when we are afraid.
神经学家曾经发现当我们害怕的时候，我们的大脑会分泌出一种化学物质，这种跟愉悦情绪相关的物质叫做多巴胺。
Exactly how much dopamine and how many receptors we have for receiving it can influence whether you are a person that enjoys being frightened or someone who would rather avoid scary movies or rides altogether.
有的人享受害怕的感觉，有的人连恐怖电影都不敢看，只能抱作一团，这种差异就跟分泌的多巴胺和接收该物质的神经末梢分布的多少有关。
So for some, letting our imaginations run wild with the possibilities of cohabitating with ghosts, although scary, may also produce a bonus euphoric high.
所以对于那些多巴胺丰富、享受害怕的那些人，充分发挥自己的想象力，与鬼共处一室的想法会让他们大脑亢奋，虽然还是有点惊悚。
Of course, believing in ghosts also allows us to believe in an existence after death, which ultimately can be comforting. That is, if you can get past the feeling that someone is standing just behind you as you listen to this.
当然，相信世界上有鬼的人也会相信死后世界的存在，因为人们能从中得到安慰。在你正在听这篇文章的时候，你有没有感觉到有人就站在你身后，静静地看着你?
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