Ever since Albert Einstein published his Special Theory of Relativity in 1905, one equation has been the bane of humans hoping to explore the stars: E=mc². In addition to informing our understanding of gravity, space, and time, this formula implies that traveling at or beyond light speed is impossible. And given how expansive the universe is, this speed limit severely restricts our ability to zip around the cosmos. But while most physics textbooks describe this speed limit, their explanations don’t always tell the whole story.自从 1905 年阿尔伯特·爱因斯坦发表狭义相对论以来，一个方程一直是人类探索恒星的祸根：E=mc²。除了加深我们对重力、空间和时间的理解之外，这个公式还意味着以光速或超光速旅行是不可能的。考虑到宇宙有多么广阔，这个速度限制严重限制了我们绕宇宙飞行的能力。但是，虽然大多数物理教科书都描述了这个速度限制，但他们的解释并不总是能说明全部情况。

In Einstein’s equation, E stands for energy, m for mass, and c for a constant— specifically, the speed of light in a vacuum. C squared is a huge number, which means it requires enormous amounts of energy to move even small amounts of mass close to the speed of light. This relationship is why the only particles that can travel at light speed are those with no mass at all, such as photons.在爱因斯坦方程中，E 代表能量，m 代表质量，c 代表常数，特别是真空中的光速。 C平方是一个巨大的数字，这意味着即使是很小的质量也需要大量的能量才能接近光速。这种关系就是为什么唯一能够以光速传播的粒子是那些完全没有质量的粒子，例如光子。

That’s the short answer for why objects with mass can’t reach or exceed light speed. But to make full use of Einstein's equation, physicists often include one more variable. This gamma represents the Lorentz Factor, which models how an object’s velocity changes the way that object experiences time, length, and other physical properties. Now, when an object’s velocity is a very small percentage of the speed of light, this variable resolves to 1, so it doesn’t impact the equation. However, when an object is moving fast enough, this denominator drops to 0. Since dividing by 0 is impossible, this breaks the equation and makes the variables therein mathematically impossible— hence the unbreakable speed limit.这就是为什么有质量的物体无法达到或超过光速的简短答案。但为了充分利用爱因斯坦方程，物理学家通常会多加入一个变量。该伽马代表洛伦兹因子，它模拟物体的速度如何改变物体经历时间、长度和其他物理属性的方式。现在，当物体的速度只占光速的很小一部分时，该变量解析为 1，因此不会影响方程。然而，当物体移动得足够快时，该分母就会降至 0。由于除以 0 是不可能的，这会破坏方程并使得其中的变量在数学上不可能 - 因此是牢不可破的速度限制。

But what does it actually mean for this math to break down? To answer that, we need to understand the physical system its modeling: spacetime. After Einstein published his theory of special relativity, his mentor Hermann Minkowski realized that— if his student was right— it would mean space and time were not two separate entities, but one connected system. And everything in the universe travels through space and time simultaneously. However, traveling through one of these vectors limits the speed at which we can travel through the other. To picture this, imagine moving north at a fixed speed. You could turn to travel east at the same speed, but moving northeast would mean you move in both directions more slowly. The tradeoffs are the same when we move through spacetime. Since our typical movement through space is so much slower than the speed of light, we mostly perceive moving through time at a relatively steady speed. But if an object managed to move through space at the speed of light, it would no longer move through time. This is the kind of time dilation charted by the Lorentz Factor, which models how time slows down for objects moving at incredibly high velocities.但这个数学模型崩溃到底意味着什么呢？为了回答这个问题，我们需要了解其建模的物理系统：时空。爱因斯坦发表狭义相对论后，他的导师赫尔曼·明可夫斯基意识到——如果他的学生是对的——那就意味着空间和时间不是两个独立的实体，而是一个相互联系的系统。宇宙中的一切事物都是同时穿越空间和时间的。然而，穿过这些矢量之一会限制我们穿过另一个矢量的速度。为了描绘这一点，想象一下以固定速度向北移动。您可以以相同的速度转向向东行驶，但向东北移动意味着您在两个方向上移动的速度都会更慢。当我们穿越时空时，权衡是相同的。由于我们在空间中的典型运动比光速慢得多，因此我们大多认为以相对稳定的速度在时间中运动。但如果一个物体能够以光速在空间中移动，它就不再能在时间中移动。这是洛伦兹因子绘制的时间膨胀类型，它模拟了以极高速度移动的物体的时间如何减慢。

This nuance is just one of several hiding in E=mc². For example, the c in Einstein’s equation refers specifically to the speed of light in a “vacuum,” which outer space approximates. But light’s speed is actually defined by what it’s traveling through. For example, when light travels through water, its speed is reduced by about 25%. And scientists can propel low mass particles like charged electrons through water at speeds faster than these photons. This means that underwater, some particles can travel faster than light; and doing so emits a ghostly blue glow known as Cherenkov radiation.这种细微差别只是 E=mc² 中隐藏的几个细微差别之一。例如，爱因斯坦方程中的 c 特指“真空”中的光速，即外层空间的近似值。但光速实际上是由它所穿过的物体决定的。例如，当光在水中传播时，其速度会降低约25%。科学家可以以比光子更快的速度推动带电电子等低质量粒子穿过水。这意味着在水下，一些粒子的运动速度可以超过光速；这样做会发出一种幽灵般的蓝色光芒，称为切伦科夫辐射。

Despite these loopholes, the major takeaway of E=mc² remains true. As far as we know, we still can't travel faster than light in a vacuum. But this hasn't stopped scientists from theorizing what might happen if we did. If you were on a spacecraft approaching light speed, your vision would likely become kaleidoscopic. The direction your ship moved would appear blue-shifted, while the things next to and behind you would be red-shifted. And if you were somehow able to reach or exceed light speed, it might even manifest as some kind of time travel— potentially letting you chat with Einstein himself to rewrite our fundamental understanding of physics.尽管存在这些漏洞，E=mc² 的主要结论仍然正确。据我们所知，我们在真空中的行进速度仍然无法超过光速。但这并没有阻止科学家们对如果我们这样做会发生什么进行理论分析。如果你乘坐接近光速的宇宙飞船，你的视野可能会变得千变万化。你的船移动的方向会出现蓝移，而你旁边和后面的东西会红移。如果你能够以某种方式达到或超过光速，它甚至可能表现为某种时间旅行——有可能让你与爱因斯坦本人聊天，重写我们对物理学的基本理解。