Eli5. How its possible for the light to travel constantly with out stop slowing down from the most old galaxies?



Eli5. How its possible for the light to travel constantly with out stop slowing down from the most old galaxies?

In: Physics

What would slow it down though?

Light is special because it has no mass and always travels at, well, the speed of light. This is one of its fundamental properties due to the laws of physics. You can’t really compare light to say, a spaceship, because it’s just not the same thing.

But almost anything can move long distances in space without slowing down. By default, things continue moving at the same speed they’re already moving unless something acts to slow them. On Earth, everything needs to fight air resistance or water resistance or friction with the ground to keep moving. But in space there’s nothing to bump into (at least it’s very rare to hit something) so if you do nothing, you keep moving.

Gravity or with what energy still move at same speed?

It is only our frame of reference that light’ travels constantly without stop’. From the frame of reference of light, no time has elapsed, it arrives instantly, hey presto, relativity. All of its energy is in motion none is in mass.

Things that have no mass MUST travel at the speed of light. It’s simply a written rule of the universe.


Fundamental conceptually innaccurate understanding of light. Light has no speed.

If youre reading a blank book, but letters appear on the page as soon as you turn the page and can see them. Do they have a speed?
They appear at the speed you turn the page, not of their own innate properties. This is not a ‘speed’ but a characteristic defined by something else.

Light doesnt move. It exists everywhere along its path as soon as its created. What you call speed of light, is the maximum speed we can change something in the universe. The speed of causality.

Because light exists everywhere along its path, theres nothing to slow down. Thats your answer.

ELI15; This is a fundamental conceptual misunderstanding. All the documentaries, science books etc would do well to change “speed of light” to “speed of causality” per Einstein.

Light does not travel in the sense we think about.

Light exists in a line along its path immediately upon being created.

When someone says light speed is X, what they mean is the speed of causality is X. The speed at which anything can experience a change in information.

So you might say? Well, isnt that the same? No, because light exists immediately along a trajectory, it doesnt have a mass to slow down. It isn’t moving like how we innately understand movement.

Counter to this is light slowing in a medium. Dont be confused. 2 different mediums are being discussed. One medium actually slows causality. The other medium does not slow causality.

1. Light appears slower in a gravity well, this is a type of medium. This is because causality slows. The rate at which our reality can experience a change in data slows.

2. Light appears to slow in a crystal or other object, because it physically interacts, is absorbed, re-emitted. Basically bounces around causing it to “appear slowed” . This is a different kind of medium. The reaction at the quantum level results in the added time not light traveling.

Normal light spreads out and its intensity decrease as it covers more distance until it fades away.

It is possible for powerful laser lights. Laser lights have single beam of light ray. So, there is very little spread and decrease in its intensity with increasing distance.

But powerful laser light rays also spread to some extent causing decrease in its intensity until it fades away at largest distance.

Before we talk about light, your question is first answered by Newton’s first law of motion which is “things at rest stay at rest, things in motion stay in motion unless acted upon by a force.” Anything in space will continue to move forever if nothing hits it or is far away from other masses so as to no be affected by gravity. On earth, things are always hitting molecules. We are surrounded by air. Gravity from earth also brings us into contact with other matter which will slow things down to a stop. On earth, we contantly need energy to overcome friction and air resistance.

Essentially, the universe squeezes the photon to stay at full velocity at all times. It doesnt slow down because the rules say it cant exist otherwise.

Photons are not ‘propelled’, they go one speed and one speed only, otherwise they dont exist.

Realistically, everything in the universe wants to go *c*, unless mass is imparted to the object/particle.

Because everything travels at 3×10^8 m/s through spacetime. Objects with mass have this ‘velocity’ pointing so they move entirely or mostly in the ‘time’ direction (a stationary object is moving at full speed through time, but not at all through space), while photons and massless particles are heading in the ‘space’ direction (really fast in space, not so fast in time).

Like a ship sailing North at a fixed speed, if it turns to point more Eastwards, its Northwards speed decreases as its Eastwards speed increases, but its overall velocity is unchanged. Here, ‘North/South’ is analgous to moving in time and ‘East/West’ is analogous to moving in space.

This quite nicely captures why space contraction and time dilation occur (though it does ignore all the details). Hopefully ELY5!

Light is the ‘most free’ state of energy. Light goes C. Any other statement is false. Doesn’t matter what your gut says, what the tarot cards say, etc. C is the highest common denominator.

If black holes dont let light escape, how does light not slow to zero….actually just remembered what someone said, and remembered that time does not pass in black holes..I never connected the 2, I figured light is stopped and time does not move. Ya just need the time to stop to keep the light from ecaping….

To disagree with nearly every other answer here.

Light doesn’t travel forever at the same speed, it does in fact slow down.

To support this is I cite the phenomenon known as cosmic background radiation.

That fuzz you can hear on an old TV or radio that isn’t tuned properly is an abundance of radio waves that we can detect.

These radio waves are actually the output from the big bang that had slowed down and lost energy over time. They used to be visible light or other higher energy radiation.