光有液态吗（光有质量吗）

提到光，大多数人只想到可见光而忽略不可见光。而当说到光的质量时，人们一般认为光没有静质量。但实际上即便是运动中的光子也是没有质量的（光是不可被停止的。迄今为止人类从未成功的使光子停止并对其称重。目前最成功的例子是Lene Hau将光束射向玻色爱因斯坦凝聚态的超冷凝物质介质，光在其中穿行时的速度才被降低到38英里／小时）。

我知道你想说因为光有动量所以用质能公式 E＝mc2 来推导光是有质量的。那么光谱中从伽马射线到微波所有波段都是光只不过波长不一样所以所携带的能量也不一样，我们很容易就可以得到以下的结果：

E (伽马射线)＝m (伽马射线) c2

E (x光)＝m (x光) c2

E (紫外线)＝m (紫外线) c2

E (可见光)＝m (可见光) c2

E (无线电波)＝m (无线电波) c2

…….

现在问题来了，它们都是以恒定的光速前进并且携带不同等级的能量，他们都是光，你把能量带入到质能公式里面得到了不同的数值，那么究竟哪个数值才是光的质量呢？

从量子力学的角度来说，根据泡利不相容原理，有着半整数自旋的两个费米子不能处于相同的量子态。这种特性使得费米子可以累积成物理实体。而光作为规范玻色子的一种是和作为组成实体物质的基础粒子 － 费米子有着本质区别的，光子（玻色子）自旋为整数，不遵守泡利不相容原理，这使得任意数量的全同玻色子（光子）可以处于相同的量子态，这种特性可简单理解为无论多少个光子叠加也不可能形成物理实体。

光是纯能量，而纯能量是不能有质量的。

另外，光速的本质是宇宙内的极限速度，任何有质量的物理实体都被禁止达到这个极限速度。

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Talking about light, most people think about visible light and ignore invisible light. For whether light has mass, people consider light has no rest mass. In fact, light has no mass regardless if a photon is traveling or not (Light can’t be stopped, human never stopped light nor measure its mass. the most practical experiment ever conducted is by Lene Hau, who successfully shot a laser through a Bose-Einstein Condensate matter and reduced the speed of light down to 38 miles per hour).

Now I know you would like to say that according to the E＝mc2 , light has energy, so it has mass. Then, there are different types of light carrying different energy level from gamma radiation to low energy level of longwave radiation, and we can easily get the following:

E (gamma ray)＝m (gamma ray) c2

E (x-ray)＝m (x-ray) c2

E (ultra-violet)＝m (ultra-violet) c2

E (visible light)＝m (visible light) c2

E (radio wave)＝m (radio wave) c2

…….

Here is the problem, they are all light, traveling at the speed of light and carrying different level of energy. You input those energy values into the equation and get different results, now which value is the mass value of light?

According to the Pauli exclusion principle in quantum mechanics, two identical fermions (half-integer spin) can not occupy the same quantum state simultaneously. This makes fermions capable to add up to real substance. While light (as Gauge Boson with integer spin) on the other hand, are not subject to the Pauli exclusion principle. So multiple photons can occupy the same quantum state. Easily to say that photons can never form real mater.

Light is pure energy, and energy has no mass.

The speed of light is essentially the extreme speed limit within the universe, any matter that has mass is forbiden to have this extreme speed.