Is objective morality possible? The short answer is no. ... and it happens to be the long answer, too, but this is a blog after all, so I'll dive deeper into why "no" is the proper answer.
First, we need to understand what objective means. Objective is defined as not influenced by personal feelings in regards to opinion on factual occurrences. It's counter is subjective, which means to be influenced by prejudices such as taste and experience. In other words, objective is rigid, untainted and non-human while subjective is very much human, personal and varying.
So, can morality be objective now that we know the definition? Before just saying no again, let's put it to the test. Is there one perfect answer for every moral conundrum? For instance, a man steals a loaf of bread from a store on a dare from his buds. Is this wrong? Sure, most would say this is wrong because he didn't pay for it, didn't earn it and he stole from another person (the store owner) who will now be negatively affected by this through lack of profits and inventory. The ramifications are far-reaching as well. The store owner may now choose to install security cameras, which costs him more money and could force him to raise his prices, and now the thief has affected an entire community. Or the owner may decide to choose a questionable (immoral) path and call his supplier and say the loaf of bread had expired before its date and demand a replacement or credit on his next order. Now he's straddling the morality line and causing problems further down the chain.
Let's start over and change some of the circumstances. A man, who's fired from his job because of a misunderstanding, gets turned down for unemployment benefits, injures himself in a car accident badly enough that he can't work but he doesn't qualify for disability, has five young children at home and he's a widower. He has no money, no family to help him and his kids are starving. In a moment of weakness and a desire to take care of his children, he happens upon a convenience store dumpster and swipes a stale loaf of bread from it to feed the five mouths at home. Is it morally wrong since the contents of the dumpster don't belong to him? Probably, but the degrees of morality are as plentiful as colors in a box of crayons, so how could there be objective morality? Is there one right answer here? If the objective punishment for thievery is to cut off the culprit's hands, do we cut all thieves' hands off, regardless of circumstances and degree?
We have larceny and petty theft for a reason, because there are varying levels of punishment for varying levels of crime. There is no one-punishment-fits-all mentality in our society. It's why we educate and hire judges, to be as impartial as possible. You may say, "A judge is forced to be objective so how can you say no to the initial question of objective morality?" But, as I mentioned at the start of this paragraph, we pass laws and set rules to give judges and lawyers a guide that we as a society agree to and vote on for such an occasion and system. Those rules are subjective because we collectively feel they are fair. It's the same with juries, who weigh the evidence and circumstances before rendering a verdict.
So why is this topic being broached on an atheism blog? Most people who believe objective morality exists believe their god is the being who possesses and sets this morality. For the sake of simplicity we'll use the Judeo-Christian god. Christians believe their morals come from the bible, which they feel houses the infallible word of god. They believe there is one set of moral standards and ethics that remains constant because they are eternal, from their eternal deity. This also has loosely become known as the Kantian Categorical Imperative, because Kant's view of an objective morality was steered by his Christian views. This, however, is the very reason his imperative is rendered biased and moot. And of course any decent reading of the bible, particularly the OT of Yahweh, will find countless horrific effronteries to any moral compass.
Here's my take on this: If there were a god, and we truly are created in "his" image, then this god is a being, and a being has opinions, and opinions are subjective by definition. "God" judges all actions based on what he/she/it believes is right, and that makes it subjective. It may be the final judgement of your actions, making it feel objective, but ultimately there's still one being making the determination, and that means it's not objective.
But we don't need a god to tell us what is right or wrong because morality is subjective by nature; it's a living, breathing thing that adjusts to the times and needs, just like the U.S. Constitution, which is not set in stone so that we may/can change it. Think of the morality of this country more than 150 years ago when people owned slaves and women were considered second-class citizens. Isn't it great to know we have progressed beyond these atrocities, that we are more moral than a "god" that a billion people still worship?
No, objective morality doesn't exist; it can't. And that's a good thing; it's the right thing.