# Why is the Speed of Light an unbreakable barrier for us?

## Understand Einstein's theory of relativity: speed limit of light, inertial frame, constant speed of light, and the absence of an absolute frame of reference.

## Why can't we go faster than the Speed of Light?

Einstein's special theory of relativity posits that the speed of light is insurmountable. However, it's crucial to understand that this is based on certain prerequisites. It's important to note that the theory doesn't rule out the possibility of exceeding the speed of light entirely.

The special theory of relativity establishes that information propagation speed can't surpass the speed of light within an inertial system, which includes the speed of any object. Therefore, objects belong to the information category. It's worth highlighting that two key elements are relevant here: the inertial frame and the speed of information propagation. One prerequisite of this theory is that the frame must be inertial.

What is an inertial system, then? It refers to a reference frame with zero acceleration. If you're motionless or moving uniformly in a straight line relative to a reference frame, that frame will be your inertial frame.

The Earth is generally considered to be an inertial system, despite moving in a circular motion. This is because the circular motion of the Earth is executed on a much larger scale and has a minimal effect on us.

As a result, in an inertial system, the rate at which information propagates cannot surpass the speed of light. Hence, in a non-inertial system, it is possible to exceed the speed of light.

Scientists often use large particle colliders to discover smaller microscopic particles. The primary method is to collide two microscopic particles at a velocity very close to the speed of light.

As an example, if the speed of microscopic particles reaches 0.9 times the speed of light, the relative speed between the two is 1.8 times the speed of light. This may seem like it surpasses the speed of light, but it doesn't violate Einstein's special theory of relativity.

This is because 1.8 times the speed of light is only the relative motion speed of microscopic particles, not their speed relative to a particular inertial system. In other words, if we consider the inertial system of the Earth, the speed of microscopic particles is impossible to surpass the speed of light.

To give another example, suppose a spaceship is traveling at the speed of light C, even though it's only a hypothetical scenario. You are running with a speed of V on the spaceship, and I am on the ground.

From my perspective, what is your speed? Is it the speed of the spaceship plus your running speed, i.e., C+V?

No, your speed is still the speed of light, not the speed of light + the speed of the spaceship.

This is because "I" am an inertial system. In this inertial system, no matter how any two speeds are combined, the final speed cannot exceed the speed of light. This is, in fact, the direct embodiment of Einstein's special theory of relativity regarding "the speed of light is the speed limit."

### What is the core of special relativity?

The principle of constant speed of light and the principle of relativity! The special theory of relativity is also based on these two fundamental postulates. Among them, the principle of relativity emphasizes the inertial system, which is often overlooked by many people. Another crucial point, in addition to the inertial system, is the principle of the constant speed of light.

### Why is the speed of light constant?

There are several popular science articles available that explain this topic, so I will not go into detail here. Essentially, the speed of light is an absolute constant, and it doesn't rely on any frame of reference. The speed of light remains exactly the same in any frame of reference.

In mathematical terms, the speed of light remains unchanged, regardless of whether it is added to any other velocity. The "dominant" nature of the speed of light implies that regardless of how quickly you try to catch up to a beam of light, its velocity will always remain constant from your perspective. Even if you approach 99% of the speed of light, you will never be able to keep pace with it. Rather, the light will continue to move away from you at its steady rate.

To test your comprehension of the constant speed of light principle, let's consider an example.

I turn on a flashlight and while it is shining, you and the light are both in motion. Your speed is half the speed of light, which is 0.5 times the speed of light. Suppose I observe the light from the flashlight traveling two kilometers, then the distance you traveled is one kilometer. Since the speed of light is constant, the light from the flashlight travels two kilometers in your eyes as well.

Now, if you observe the light from the flashlight, how far would you see it travel in your reference frame? Would it still be two kilometers?

No, the reference frame has changed, and in your reference frame, the light from the flashlight only travels one kilometer. This is because you and the light are both moving, and your relative speed is 0.5 times the speed of light. Since the speed of light is constant, dividing the distance the light traveled by my time is equal to dividing the distance the light traveled by your time, and the result is always the speed of light.

It is evident that my time is moving faster than your time, indicating time dilation. However, the above examples are just simplified explanations to help us understand the principles of the constant speed of light and time dilation. Although they are not precise, they are adequate for general scientific comprehension.

The absence of an absolute frame of reference is the primary reason why it is referred to as "relativity." In the world, there is no fixed reference frame. The concept of "ether," which was previously considered an absolute frame of reference over a century ago, has been dismissed.

Under the principles of special relativity, all inertial frames are equally valid, and physical laws apply equally in all of them. Therefore, when analyzing a problem, we only need to consider one inertial system, rather than analyzing all of them. For instance, the famous twin paradox can be analyzed from the frame of reference of either the elder or younger twin, and the result will be the same.

In the previous example, I used "my" frame of reference to analyze the problem. However, you can also use your own frame of reference to analyze the problem, but the outcome will still be the same. If you are interested, you can try to analyze it for yourself.

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